is the Science
; The branch of the natural sciences dealing with the
Substances and their
Glossary of Chemistry Terms
Chemistry Stack Exchange
is a question and answer site for scientists.
- Do it Yourself
is a scientist trained in the study of chemistry.
Chemists study the composition of matter
and its properties. Chemists
carefully describe the properties they study in terms of quantities,
with detail on the level of molecules and their component
Chemists carefully measure substance proportions, reaction rates, and
other chemical properties. Drug
is a form of matter that has constant chemical
composition and characteristic properties. It cannot be separated into
components by physical separation methods, i.e., without breaking
. Chemical substances can be chemical elements, chemical
compounds, ions or alloys.
is any of a material's properties that becomes
evident during, or after, a chemical reaction; that is, any quality that
can be established only by changing a substance's chemical identity.
Simply speaking, chemical properties cannot be determined just by
viewing or touching the substance; the substance's internal
must be affected greatly for its chemical properties to be investigated.
When a substance goes under a chemical reaction, the properties will
change drastically, resulting in chemical change. However, a catalytic
property would also be a chemical property.
is the identity, and relative number, of the elements
that make up any particular compound. It refers to the
arrangement, type, and ratio of atoms in molecules
substances. Chemical composition varies when chemicals are added or
subtracted from a substance, when the ratio of substances changes, or
when other chemical changes occur in chemicals. The chemical composition
of a pure substance corresponds to the relative amounts of the elements
that constitute the substance itself. It can be expressed by the
empirical formula. For example the formula for water is H2O: this means
that each molecule is constituted by 2 atoms of hydrogen (H) and 1 atom
of oxygen (O). The chemical composition of a mixture can be defined as
the distribution of the single substances that constitute the mixture,
called "components". In other words, it is defined giving the
concentration of each component. Because there are different ways to
define the concentration of a component, as a consequence there are also
different ways to define the composition of a mixture. For example it can
be expressed as molar fraction, volume fraction, mass fraction, molality,
molarity or normality. Chemical composition of a mixture can be
represented graphically in plots like ternary plot and quaternary plot.
is a material system made up of two or more different substances which
are mixed but are not combined
chemically. A mixture refers to the
physical combination of two or more substances in which the identities
are retained and are mixed in the form of solutions, suspensions, and
is a process
that leads to the
of one set of
chemical substances to another. Classically, chemical reactions
encompass changes that only involve the positions of
forming and breaking of chemical bonds
between atoms, with no change to
the nuclei (no change to the elements present), and can often be
described by a chemical equation.
kind of action that occurs as two or more objects have an
A bacterial enzyme enables reactions
is where one reactant undergoes bond breaking
and/or forming to yield different products.
is where two reactants collide and then
undergo bond breaking and/or forming to yield different products.
Termolecular association reactions
two reactants collide to form a molecular complex with a new chemical
bond between the two reactants and a third molecule
, known as the bath
gas, removes some of the internal kinetic
of that molecule to stabilize it. New class of chemical
reactions involving three molecules that each participate in the breaking
and forming of chemical bonds
. The reaction of three different molecules
is enabled by an "ephemeral collision complex," formed from the collision
of two molecules, which lives long enough to collide with a third
molecule. Cause and
is a sub-discipline
of chemistry that involves the chemical reactions of unstable and
radioactive elements where both electronic and
refers to the similarity of chemical
elements, molecules or chemical compounds with respect to either
structural or functional qualities, i.e. the effect that the chemical
compound has on reaction partners in inorganic or biological settings.
Biological effects and thus also similarity of effects are usually
quantified using the biological activity of a compound. In general
terms, function can be related to the chemical activity of compounds
chemical substance to undergo a transformation through a chemical
reaction to transform other chemical substances. Examples include
and more. Breaking or making of chemical
bonds involves Energy
, which may be either
absorbed or evolved from a chemical system.
is a chemistry subdiscipline involving the
scientific study of the structure
, properties, and reactions of organic
compounds and organic materials, i.e., matter in its various forms that
contain carbon atoms. Study of structure includes many physical and
chemical methods to determine the chemical composition and the chemical
constitution of organic compounds and materials. Study of properties
includes both physical properties and chemical properties, and uses
similar methods as well as methods to evaluate chemical reactivity, with
the aim to understand the behavior of the organic matter in its pure
form (when possible), but also in solutions, mixtures, and fabricated
forms. The study of organic reactions includes probing their scope
through use in preparation of target compounds (e.g., natural products,
drugs, polymers, etc.) by chemical synthesis, as well as the focused
study of the reactivities of individual organic molecules, both in the
laboratory and via theoretical (in silico) study.
Organic Materials Database
deals with the synthesis and behavior of inorganic and organometallic
compounds. This field covers all chemical compounds except the myriad
(carbon based compounds, usually containing C-H
bonds), which are the subjects of organic chemistry. The distinction
between the two disciplines is far from absolute, as there is much
overlap in the subdiscipline of organometallic chemistry. It has
applications in every aspect of the chemical industry, including
catalysis, materials science, pigments, surfactants, coatings,
medications, fuels, and agriculture.
is the study of macroscopic,
, subatomic, and particulate phenomena in chemical systems in
terms of the principles, practices and concepts of physics such as
motion, energy, force
, quantum chemistry,
statistical mechanics, analytical dynamics and chemical equilibrium.
is a subfield of study within physical
chemistry concerned with the interaction of Light
systems. It is an active domain of investigation. One of the pioneers of
this field of
was the German electrochemist Heinz Gerischer. The
interest in this domain is high in the context of development of
renewable energy conversion and
is the branch of chemistry concerned with the
chemical effects of light
Generally, this term is used to describe a chemical reaction caused by
absorption of ultraviolet (wavelength from 100 to 400 nm), visible light
(400 – 750 nm) or infrared radiation (750 – 2500 nm). In nature,
photochemistry is of immense importance as it is the basis of
vision, and the formation of vitamin D with
. Photochemical reactions proceed differently than
temperature-driven reactions. Photochemical paths access high energy
intermediates that cannot be generated thermally, thereby overcoming
large activation barriers in a short period of time, and allowing
reactions otherwise inaccessible by thermal processes. Photochemistry is
also destructive, as illustrated by the photodegradation of plastics.
sometimes called biological
chemistry, is the study of chemical
processes within and relating to living
. By controlling
information flow through biochemical signaling and the flow of chemical
energy through metabolism, biochemical processes give rise to the
complexity of life. Over the last decades of the 20th century,
biochemistry has become so successful at explaining living processes
that now almost all areas of the life sciences from botany to medicine
to genetics are engaged in biochemical research. Today, the main focus
of pure biochemistry is on understanding how biological molecules give
rise to the processes that occur within living cells, which in turn
relates greatly to the study and understanding of tissues, organs, and
whole organisms-that is, all of biology.
scientists that are trained in biochemistry.
is a chemistry subdiscipline that deals with the
structures, chemical synthesis and properties of
, primarily synthetic
such as plastics
and elastomers. Polymer chemistry is
related to the broader field of
, which also encompasses
materials that have the ability to return from a deformed state
shape) to their original (permanent) shape induced by an
external stimulus (trigger), such as temperature change. Shape-memory
materials "remember" their original shape and return to it after they are
deformed. They are commonly metallic alloys that make possible
"unbreakable" eyeglass frames and quieter jet engines.
Ames Laboratory, UConn discover superconductor with bounce
is a process of reacting monomer
molecules together in
a chemical reaction to form polymer chains or three-dimensional networks.
There are many forms of polymerization and different systems exist to
categorize them. Polymers
are high molecular mass
compounds formed by polymerization of
which is a molecule that, as a unit, binds chemically or supramolecularly
to other molecules to form a supramolecular polymer.
studies and uses instruments and methods used to separate, identify, and
quantify matter. In practice separation, identification or
quantification may constitute the entire analysis or be combined with
another method. Separation isolates analytes. Qualitative analysis
identifies analytes, while quantitative analysis determines the
numerical amount or concentration.
is the science that uses the tools and
principles of chemistry to explain the mechanisms behind major
geological systems such as the Earth's crust and its oceans. The realm
of geochemistry extends beyond the Earth, encompassing the entire Solar
System and has made important contributions to the understanding of a
number of processes including mantle convection, the formation of
planets and the origins of granite and basalt.
are disciplines at the intersection of
chemistry, especially synthetic organic chemistry, and pharmacology and
various other biological specialties, where they are involved with
design, chemical synthesis and development for market of pharmaceutical
agents, or bio-active molecules (drugs).
is a branch of chemistry that uses
computer simulation to assist in solving chemical problems. It uses
methods of theoretical chemistry, incorporated into efficient computer
programs, to calculate the structures and properties of molecules and
solids. It is necessary because, apart from relatively recent results
concerning the hydrogen molecular ion (dihydrogen cation, see references
therein for more details), the quantum many-body problem cannot be
solved analytically, much less in closed form. While computational
results normally complement the information obtained by chemical
experiments, it can in some cases predict hitherto unobserved chemical
phenomena. It is widely used in the design of new drugs and materials.
is a geometric property of some
molecules and ions. A chiral molecule/ion is non-superposable on its
mirror image. The presence of an asymmetric carbon center is one of
several structural features that induce chirality in organic and
a combination of two or more entities that together form something new;
alternately, it refers to the creating of something by artificial means,
or recreating or imitating a chemical compound or substance produced by a
living organism that is
found in nature
The process of producing a chemical compound
, usually by the union of
simpler chemical compounds. Alchemy
is a multi-step, enzyme-catalyzed process where
substrates are converted into more complex products in living organisms.
In biosynthesis, simple compounds are modified, converted into other
compounds, or joined together to form macromolecules. This process often
consists of metabolic pathways. Some of these biosynthetic pathways are
located within a single cellular organelle, while others involve enzymes
that are located within multiple cellular organelles. Examples of these
biosynthetic pathways include the production of lipid membrane components
and nucleotides. The prerequisite elements for biosynthesis include:
precursor compounds, chemical energy (e.g. ATP), and catalytic enzymes
which may require coenzymes
(e.g.NADH, NADPH). These elements create
monomers, the building blocks for macromolecules. Some important
biological macromolecules include: proteins, which are composed of amino
acid monomers joined via peptide bonds, and DNA molecules, which are
composed of nucleotides joined via phosphodiester bonds.
is the process whereby biological cells
generate new proteins
; it is balanced by the loss of cellular proteins
via degradation or export. Translation, the assembly of amino acids by
ribosomes, is an essential part of the biosynthetic pathway, along with
generation of messenger RNA
aminoacylation of transfer RNA (tRNA), co-translational transport, and
post-translational modification. Protein biosynthesis is strictly
regulated at multiple steps. They are principally during transcription
(phenomena of RNA synthesis from DNA template) and translation (phenomena
of amino acid assembly from RNA).
biologically important organic compounds containing amine (-NH2) and
carboxyl (-COOH) functional groups, along with a side-chain (R group)
specific to each amino acid. The key elements of an amino acid are
, and nitrogen
, though other elements are found
in the side-chains of certain amino acids. About 500 amino acids are
(though only 20 appear in the
) and can be classified
in many ways. Nine proteinogenic amino acids are called "essential" for
humans because they cannot be created from other compounds by the human
body and so must be taken in as
. Others may be conditionally
essential for certain ages or medical conditions. Essential amino acids
may also differ between species. Because of their biological
significance, amino acids are important in
and are commonly
used in nutritional supplements
, fertilizers, and food technology.
Industrial uses include the production of drugs, biodegradable plastics,
and chiral catalysts. Amino acids perform critical roles in processes
BCAA or Branched Chain Amino Acids
acids are the
of protein. There are nine
essential amino acids in total
, but there's a key trio that helps
you maintain muscle: leucine, isoleucine, and valine. Of these three,
leucine is the muscle-building powerhouse. The beauty of BCAA supplements
is they can be easily used during
to reduce fatigue, accelerate recovery, reduce muscle
soreness, and improve the use of fat for energy. BCAAs are well known for
triggering protein synthesis.
is an α-amino
acid used in the biosynthesis of proteins.
α-amino acid that is used in the biosynthesis of proteins. It is
essential in humans, meaning the body cannot
, and must be ingested in our diet.
is an α-amino
acid that is used in the biosynthesis of proteins
Human dietary sources are any proteinaceous foods such as meats, dairy
products, soy products, beans and legumes.
are natural biological or artificially manufactured short chains of amino
acid monomers linked by peptide (amide) bonds.
is the increase in the rate of a chemical reaction
due to the
participation of an additional substance called a catalyst. In most
cases, reactions occur faster with a catalyst because they require less
activation energy. Furthermore, since they are not consumed in the
catalyzed reaction, catalysts can continue to act repeatedly. Often only
tiny amounts are required in principle.
. A single chemical reaction is said to have
undergone autocatalysis, or be autocatalytic, if one of the reaction
products is also a reactant and therefore a catalyst in the same or a
coupled reaction. The reaction is called an autocatalytic reaction.
Order of Reaction
in chemical kinetics, the order of
with respect to a given substance (such as reactant, catalyst or
product) is defined as the index, or exponent, to which its concentration
term in the rate equation is raised.
macromolecular biological catalysts. Enzymes accelerate
. The molecules upon which
enzymes may act are called substrates and the enzyme converts the
substrates into different molecules known as products. Almost all
metabolic processes in the cell need enzymes in order to occur at rates
fast enough to sustain life. The set of enzymes made in a cell
determines which metabolic pathways occur in that
. The study of
enzymes is called
and a new field of pseudoenzyme analysis has
recently grown up, recognising that during evolution, some enzymes have
lost the ability to carry out biological catalysis, which is often
reflected in their amino acid
unusual 'pseudocatalytic' properties. Enzymes are known to catalyze more
than 5,000 biochemical reaction types. Most enzymes are
, although a few are catalytic
latter are called ribozymes. Enzymes' specificity comes from their unique
three-dimensional structures. Like all catalysts, enzymes increase the
reaction rate by lowering its activation energy. Some enzymes can make
their conversion of substrate to product occur many millions of times
faster. An extreme example is orotidine 5'-phosphate decarboxylase, which
allows a reaction that would otherwise take millions of years to occur in
milliseconds. Chemically, enzymes are like any catalyst and are not
consumed in chemical reactions, nor do they alter the equilibrium of a
reaction. Enzymes differ from most other catalysts by being much more
specific. Enzyme activity can be affected by other molecules: inhibitors
are molecules that decrease enzyme activity, and activators are molecules
that increase activity. Many therapeutic drugs
and poisons are enzyme inhibitors
. An enzyme's activity decreases
markedly outside its optimal temperature
. Some enzymes are
used commercially, for example, in the synthesis of antibiotics. Some
household products use enzymes to speed up chemical reactions: enzymes in
biological washing powders break down protein, starch or fat stains on
clothes, and enzymes in meat tenderizer break down proteins into smaller
molecules, making the meat easier to chew.
is a non-protein chemical compound or
metallic ion that is required for a Protein's
biological activity to
happen. These proteins are commonly enzymes, and cofactors can be
considered "helper molecules" that assist in biochemical transformations.
The rates at which this happen are characterized by enzyme kinetics.
Cofactors can be subclassified as either inorganic ions or complex
latter of which is mostly derived from vitamins and other organic
essential nutrients in small amounts. A coenzyme that is tightly or even
covalently bound is termed a prosthetic group. Cosubstrates are
transiently bound to the protein and will be released at some point, then
get back in. The prosthetic groups, on the other hand, are bound
permanently to the protein. Both of them have the same function, which is
to facilitate the reaction of enzymes and protein. Additionally, some
sources also limit the use of the term "cofactor" to inorganic
substances. An inactive enzyme without the cofactor is called an
apoenzyme, while the complete enzyme with cofactor is called a holoenzyme.
Some enzymes or enzyme complexes require several cofactors. For example,
the multienzyme complex pyruvate dehydrogenase at the junction of
glycolysis and the citric acid cycle requires five organic cofactors and
one metal ion: loosely bound thiamine pyrophosphate (TPP), covalently
bound lipoamide and flavin adenine dinucleotide (FAD), and the
cosubstrates nicotinamide adenine dinucleotide (NAD+) and coenzyme A
(CoA), and a metal ion (Mg2+). Organic cofactors are often vitamins or
made from vitamins. Many contain the nucleotide adenosine monophosphate
(AMP) as part of their structures, such as ATP, coenzyme A, FAD, and NAD+.
This common structure may reflect a common evolutionary origin as part of
ribozymes in an ancient RNA world. It has been suggested that the AMP
part of the molecule can be considered to be a kind of "handle" by which
the enzyme can "grasp" the coenzyme to switch it between different
Cells and Longevity
also known as reaction kinetics, is the study of rates of
chemical processes. Chemical kinetics includes investigations of how
different experimental conditions can influence the speed of a chemical
reaction and yield information about the reaction's mechanism and
transition states, as well as the construction of mathematical models
that can describe the characteristics of a chemical reaction.
are chemical products derived from petroleum.
Some chemical compounds made from petroleum are also obtained from other
fossil fuels, such as coal or natural gas, or renewable sources such as
corn or sugar cane.
is a water soluble mixture of different dyes extracted from lichens. It
is often absorbed onto filter paper to produce one of the oldest forms of
, used to test materials for acidity.
of a chemical compound is a graphic
representation of the molecular structure, showing how the atoms are
arranged. The chemical bonding within the molecule is also shown, either
explicitly or implicitly. Unlike chemical formulas, which have a limited
number of symbols and are capable of only limited descriptive power,
structural formulas provide a complete geometric representation of the
molecular structure. For example, many chemical compounds exist in
different isomeric forms, which have different enantiomeric structures
but the same chemical formula. A structural formula is able to indicate
arrangements of atoms in three dimensional space in a way that a chemical
formula may not be able to do. Also known as
Chemical equations usually do not come already
balanced. ... Therefore, we must finish our chemical reaction with as
many atoms of each element as when we started. Example #1: Balance the
following equation: H2 + O2 ---> H2O. It is an unbalanced equation
(sometimes also called a skeleton equation). A skeleton equation is just
a way of using the formulas to indicate the chemicals that were involved
in the chemical reaction. "Mg + O2 MgO." This skeleton equation shows
that magnesium reacts with oxygen to form magnesium oxide.
is the process that creates new atomic
nuclei from pre-existing nucleons, primarily protons and neutrons.
is the thermal motion of all (liquid or
gas) particles at temperatures above absolute zero. The rate of this
movement is a function of temperature, viscosity of the fluid and the
size (mass) of the particles. Diffusion explains the net flux of
molecules from a region of higher concentration to one of lower
concentration. Once the concentrations are equal the molecules continue
to move, but since there is no concentration gradient the process of
molecular diffusion has ceased and is instead governed by the process of
self-diffusion, originating from the random motion of the molecules. The
result of diffusion is a gradual mixing of material such that the
distribution of molecules is uniform. Since the molecules are still in
motion, but an equilibrium has been established, the end result of
molecular diffusion is called a "dynamic equilibrium". In a phase with
uniform temperature, absent external net forces acting on the particles,
the diffusion process will eventually result in complete mixing.
is the net movement of molecules or atoms from a
region of high concentration (or high chemical potential) to a region of
low concentration (or low chemical potential). This is also referred to
as the movement of a substance down a concentration gradient. A gradient
is the change in the value of a quantity (e.g., concentration, pressure,
temperature) with the change in another variable (usually distance). For
example, a change in concentration over a distance is called a
concentration gradient, a change in pressure over a distance is called a
pressure gradient, and a change in temperature over a distance is a
called a temperature gradient.
is a property of a system or of a
material itself or within. It is independent of how much of the material
is present and is independent of the form of the material, e.g., one
large piece or a collection of small particles. Intrinsic properties are
dependent mainly on the chemical composition or structure of the
is the determination of the absolute
or relative abundance (often expressed as a concentration) of one,
several or all particular substance(s) present in a sample.
is a protein molecule that receives chemical
signals from outside a cell. When such chemical signals bind to a
receptor, they cause some form of cellular/tissue response, e.g. a change
in the electrical activity of a cell. In this sense, a receptor is a
protein-molecule that recognizes and responds to endogenous chemical
signals, e.g. an acetylcholine receptor recognizes and responds to its
endogenous ligand, acetylcholine. However, sometimes in pharmacology, the
term is also used to include other proteins that are drug targets, such
as enzymes, transporters and ion channels.
are substances that, in aqueous solution, are slippery
to the touch, taste astringent, change the color of indicators (e.g.,
turn red litmus paper blue), react with acids to form salts, promote
certain chemical reactions (base catalysis), accept protons from any
proton donor, and/or contain completely or partially displaceable OH−
ions. Examples of bases are the hydroxides of the alkali metals and
alkaline earth metals (NaOH, Ca(OH)2, etc.).
Periodic Table of Elements
118 different Elements and more than 109 different types of atom
- one for each element. Only the first 92 elements in the table are
naturally found. Matter
Periodic Table of Elements
Wiki Periodic Table
(wiki periodic table)
Earth & Sky Chart
means "single atom
." It is usually applied to gases: a monatomic gas is
one in which atoms are not bound to each other. All chemical elements
will be monatomic in the gas phase at sufficiently high temperatures. The
thermodynamic behavior of monatomic gas is extremely simple when compared
to polyatomic gases because it is free of any rotational or vibrational
are molecules composed of only two atoms, of the same or
different chemical elements.
are all odorless, colorless, monatomic gases with
very low chemical reactivity. The six noble gases that occur naturally
are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the
radioactive radon (Rn). Oganesson (Og) is predicted to be a noble gas as
well, but its chemistry has not yet been investigated.
is a chemical
element with symbol He and atomic number 2
. It is a colorless, odorless,
tasteless, non-toxic, inert, monatomic gas, the first in the noble gas
group in the periodic table. Its boiling point
is the lowest among all
the elements. After hydrogen
, helium is the second lightest and second
most abundant element in the observable universe, being present at about
24% of the total elemental mass, which is more than 12 times the mass of
all the heavier elements combined. Its abundance is similar to this
figure in the Sun and in Jupiter. This is due to the very high nuclear
binding energy (per nucleon) of helium-4 with respect to the next three
elements after helium. This helium-4 binding energy also accounts for why
it is a product of both nuclear fusion and radioactive decay
. Most helium
in the universe is helium-4, and is believed to have been formed during
the Big Bang. Large amounts of new helium are being created by
of hydrogen in stars
A Tour of
the Periodic Table
Periodic Table of
Elements - Chemistry: A Volatile History - BBC Four
Uus element 117 -
is the number of Protons.
Relative Atomic Mass
is a dimensionless physical quantity,
the ratio of the average mass
of atoms of an element (from a single given
sample or source) to 1⁄12 of the mass of an atom of carbon-12
the unified atomic mass unit).
is the distribution of electrons
an atom or molecule (or other physical structure) in atomic or molecular
is a way of describing delocalized electrons
within certain molecules or polyatomic ions where the bonding cannot be
expressed by one single Lewis structure. A molecule or ion with such
delocalized electrons is represented by several contributing structures
(also called resonance structures or canonical structures).
Rare Earth Minerals
Mineral or Element?
is any naturally occurring, inorganic substance, often additionally
characterized by an exact crystal structure. A solid homogeneous
inorganic substances occurring in nature having a definite chemical
composition. Its chemical structure can be exact, or can vary within
is any metal
that is found in its metallic form, either pure or as an
alloy, in nature.
is a mixture
of metals or a mixture of a metal and another element. Alloys are defined
by a metallic bonding character.
is a chemical element that mostly lacks metallic attributes. Physically,
nonmetals tend to be highly volatile (easily vaporized), have low
elasticity, and are good
and electricity; chemically, they tend to have high ionization energy and
electronegativity values, and gain or share electrons when they react
with other elements or compounds. Seventeen elements are generally
classified as nonmetals; most are gases (hydrogen, helium, nitrogen,
oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon); one
is a liquid (bromine), and a few are solids (carbon, phosphorus, sulfur,
selenium, and iodine).
is any chemical element which has properties in between
those of metals and nonmetals, or that has a mixture of them. There is
neither a standard definition of a metalloid nor complete agreement on
the elements appropriately classified as such. Despite the lack of
specificity, the term remains in use in the literature of chemistry.
, the smallest piece that we can
split matter into (except for subatomic particles and other things.
Elements often are stacked together with other elements to form minerals.
Native elements that occur naturally are also considered minerals.
Native Element Minerals
are those elements that occur in nature in
uncombined form with a distinct mineral structure. The elemental class
includes metals and intermetallic elements, naturally occurring alloys,
semi-metals and non-metals. The Nickel–Strunz classification system also
includes the naturally occurring phosphides, silicides, nitrides and
is a species of atoms having the same number of protons in
their atomic nuclei. There are 118 elements that have been identified, of
which the first 94 occur naturally on Earth with the remaining 24 being
synthetic elements. There are 80 elements that have at least one stable
isotope and 38 that have exclusively radioactive isotopes, which decay
over time into other elements. Iron is the most abundant element (by
mass) making up Earth, while oxygen is the most common element in the
Earth's crust. Chemical elements constitute all of the ordinary matter of
is a chemical element that does not occur naturally
on Earth, and can only be created artificially. So far, 24 synthetic
elements have been created (those with atomic numbers 95–118). All are
unstable, decaying with half-lives ranging from 15.6 million years to a
few hundred microseconds. Seven other elements were first created
artificially and thus considered synthetic, but later discovered to exist
naturally (in trace quantities) as well; among them
—first synthesized in 1940—the one best known to laypeople,
because of its use in atomic bombs and
are the chemical elements in group 16 of the periodic
table. This group is also known as the oxygen family. It consists of the
elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the
radioactive element polonium (Po). The chemically uncharacterized
synthetic element livermorium (Lv) is predicted to be a chalcogen as
well. Often, oxygen is treated separately from the other chalcogens,
sometimes even excluded from the scope of the term "chalcogen"
altogether, due to its very different chemical behavior from sulfur,
selenium, tellurium, and polonium. The word "chalcogen" is derived from a
combination of the Greek word khalkόs (χαλκός) principally meaning copper
(the term was also used for bronze/brass, any metal in the poetic sense,
ore or coin), and the Latinised Greek word genēs, meaning born or
are a composed of one or more minerals.
is formed when two or more
join together chemically.
All molecules are in constant
of a liquid
have more freedom of
movement than those in a solid. Molecules in a gas have the greatest
degree of motion. Heat
, temperature and the
of molecules are all related.
is a measure of the
average kinetic energy
of the molecules
in a material. Nano Size
is molecule that is present in living
large macromolecules such as proteins
, lipids, and
nucleic acids, as well as small molecules such as primary metabolites,
secondary metabolites, and natural products. A more general name for
this class of material is biological materials. Biomolecules are usually
endogenous but may also be exogenous. For example, pharmaceutical drugs
may be natural products or semisynthetic (biopharmaceuticals) or they
may be totally synthetic. Compounds
is a computer simulation method for studying the physical
movements of atoms and molecules, and is thus a type of N-body
. The atoms and
molecules are allowed to interact for a fixed period of time, giving a
view of the dynamic evolution of the system. In the most common version,
the trajectories of atoms and molecules are determined by numerically
solving Newton's equations of
for a system
of interacting particles, where forces between the particles and their
potential energies are calculated using interatomic potentials or
molecular mechanics force fields. The method was originally developed
within the field of theoretical physics in the late 1950s but is applied
today mostly in chemical physics, materials science and the modelling of
biomolecules. Differential Equations
is a large molecule
, or macromolecule, composed of many repeated
subunits. Because of their broad range of properties, both synthetic and
natural polymers play an essential and ubiquitous role in everyday life.
Polymers range from familiar synthetic plastics such as polystyrene to
natural biopolymers such as DNA and proteins that are fundamental to
biological structure and function. Polymers, both natural and synthetic,
are created via polymerization of many small molecules, known as
monomers. Their consequently large molecular mass relative to small
molecule compounds produces unique physical properties, including
toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals.
polymers produced by living organisms; in other words, they are
. Since they are polymers, biopolymers contain monomeric
units that are covalently bonded to form larger structures. There are
three main classes of biopolymers, classified according to the monomeric
units used and the structure of the biopolymer formed: polynucleotides (RNA
), which are long polymers composed of 13 or more nucleotide
monomers; polypeptides, which are short polymers of amino acids; and
polysaccharides, which are often linear bonded polymeric carbohydrate
structures. Other examples of biopolymers include rubber, suberin,
melanin and lignin.
the design and testing of molecular properties, behavior and interactions
in order to assemble better materials, systems, and processes for
specific functions. This approach, in which observable properties of a
macroscopic system are influenced by direct alteration of a molecular
structure, falls into the broader category of “bottom-up” design.
is a variation in a single nucleotide
that occurs at a specific position in the
, where each variation is
present to some appreciable degree within a population.
that serve as the monomers, or subunits, of nucleic
acids like DNA and RNA
. The building
blocks of nucleic acids, nucleotides are composed of a nitrogenous base,
a five-carbon sugar (ribose or deoxyribose), and at least one phosphate
group. Thus a nucleoside plus a phosphate group yields a nucleotide.
is a molecule
that may bind chemically or supramolecularly to other molecules to form a
is a polymer whose monomer repeat units are
held together by noncovalent bonds. Non-covalent forces that hold
supramolecular polymers together include coordination, π-π interactions,
and hydrogen bonding. Supramolecular polymers can have physical
properties similar to plastic materials, while having better
processability and better recycling and self-healing properties, thanks
to their reversible transition from monomer to polymer structure.
concerns the molecular basis of biological
activity between biomolecules in the various systems of a cell, including
the interactions between DNA, RNA, and proteins and their biosynthesis,
as well as the regulation of these interactions
Automated Small-Molecule Synthesis
are molecules composed of only two atoms, of the same or
different chemical elements.
is a molecule that may bind chemically or supramolecularly to other
molecules to form a (supramolecular) polymer.
is a lasting attraction between atoms that
enables the formation of chemical compounds
. The bond may result from the
electrostatic force of attraction between atoms with opposite charges, or
through the sharing of electrons as in the covalent bonds. The strength
of chemical bonds varies considerably; there are "strong bonds" or
"primary bond" such as metallic, covalent or ionic bonds and "weak bonds"
or "secondary bond" such as Dipole-dipole interaction, the London
dispersion force and hydrogen bonding.
also called a molecular bond, is a chemical bond that involves the
sharing of electron pairs
between atoms. These electron pairs are known
as shared pairs or bonding pairs, and the stable balance of attractive
and repulsive forces between atoms, when they share electrons, is known
as covalent bonding. For many molecules, the sharing of electrons allows
each atom to attain the equivalent of a full outer shell, corresponding
to a stable electronic configuration.
is a general process in which molecules (or ionic
compounds such as salts, or complexes) separate or split into smaller
particles such as atoms, ions or radicals, usually in a reversible
manner. For instance, when an acid dissolves in water, a covalent bond
between an electronegative atom and a hydrogen atom is broken by
heterolytic fission, which gives a proton (H+) and a negative ion.
Dissociation is the opposite of recombination.
is the process of cleaving a covalent bond where one
previously bonded species takes both original bonding electrons from the
other species. During heterolytic bond cleavage of a neutral molecule, a
cation and an anion will be generated. Most commonly the more
electronegative atom keeps the pair of electrons becoming anionic while
the more electropositive atom becomes cationic. Heterolytic fission
almost always happens to single bonds, the process usually produces two
fragment species. The energy required to break the bond is called the
heterolytic bond dissociation energy, which is not equivalent to
homolytic bond dissociation energy commonly used to represent the energy
value of a bond.
is a geometric property of some molecules and ions. A chiral molecule/ion
is non-superposable on its mirror image. The presence of an asymmetric
carbon center is one of several structural features that induce chirality
in organic and inorganic molecules.
is an electrostatic attraction between two polar groups
that occurs when a hydrogen (H) atom, covalently bound to a highly
electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F),
of another highly electronegative atom nearby.
Hydrogen bonds can occur between molecules (intermolecular) or within
different parts of a single molecule (intramolecular). Depending on the
nature of the donor and acceptor atoms which constitute the bond, their
geometry, and environment, the energy of a hydrogen bond can vary between
1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals
interaction, and weaker than covalent or ionic bonds. This type of bond
can occur in inorganic molecules such as water and in organic molecules
like DNA and proteins. Intermolecular hydrogen bonding is responsible for
the high boiling point of water (100 °C) compared to the other group 16
hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen
bonding is partly responsible for the secondary and tertiary structures
of proteins and nucleic acids. It also plays an important role in the
structure of polymers, both synthetic and natural.
Water in Space
is a molecule that contains at least two different
. Every combination of atoms is a molecule, but not
all molecules are
. Hydrogen gas (H2) is a molecule,
but not a compound because it is made of only one element.
(H2O) can be called a molecule or a compound because it is made
of hydrogen (H) and oxygen (O) atoms.
is an entity consisting of two or more
, at least two from different
chemical elements, which associate via chemical bonds. There are four
types of compounds, depending on how the constituent atoms are held
together: molecules held together by covalent bonds, ionic compounds held
together by ionic bonds, intermetallic compounds held together by
metallic bonds, and certain complexes held together by coordinate
covalent bonds. Many chemical compounds have a unique numerical
identifier assigned by the Chemical Abstracts Service (CAS): its CAS
chemical compound where there is an absence of carbon in its
composition, and is of a non-biologic origin, and cannot be found or
incorporated into a living organism.
is virtually any chemical compound that contains carbon
, although a
consensus definition remains elusive and likely arbitrary. Organic
compounds are rare terrestrially, but of central importance because all
known life is based on organic compounds. The most basic petrochemicals
are considered the building blocks of organic chemistry.
There are now more than ten million
known by chemists.
Carbon Atoms make up 85% of all known compounds?
can make around 1.7 million different compounds?
is the more abundant carbon of the two stable
isotopes, amounting to 98.93% of the element carbon; its abundance is due
to the triple-alpha process by which it is created in
. Carbon-12 is of particular importance
in its use as the standard from which atomic masses of all nuclides are
measured: its mass number is 12 by definition and contains
neutrons and 6
is a chemical
element with symbol C and atomic number 6. It is nonmetallic and
tetravalent—making four electrons available to form covalent chemical
bonds. Three isotopes occur naturally, 12C and 13C being stable, while
14C is a radioactive isotope, decaying with a half-life of about 5,730
years. Carbon is one of the few elements known since
, Carbon (6C) has 15 known isotopes, from 8C to 22C, of which
12C and 13C are stable.
of a particular chemical element which
differ in neutron
. All Isotopes
of a given element have the
same number of protons
in each atom
is a key component of all known
on Earth. Complex molecules
are made up of carbon bonded with other elements, especially
, and carbon can bond with all of these because of
its four valence electrons
. Carbon is abundant on Earth. It is also
lightweight and relatively small in size, making it easier for
manipulate carbon molecules. It is assumed in
astrobiology that if life exists somewhere else in the universe, it will
also be carbon-based.
Blocks of Life
- Human Body
Chem 4 Kids
is a thermochemical
material at elevated temperatures in the absence of oxygen (or any
halogen). It involves the simultaneous change of chemical composition and
physical phase, and is irreversible.
is a sub-discipline of analytical chemistry
covering the quantitative measurement of xenobiotics (drugs and their
metabolites, and biological molecules in unnatural locations or
concentrations) and biotics (macromolecules, proteins, DNA, large
molecule drugs, metabolites) in biological systems.
is the branch of physics
which deals with the
Thermodynamics is the branch of
and their relation to
energy and work. It states that the behavior of these quantities is
governed by the four laws of thermodynamics, irrespective of the
composition or specific properties of the material or system in
question. The laws of thermodynamics are explained in terms of
microscopic constituents by statistical mechanics. Thermodynamics
applies to a wide variety of topics in science and engineering,
especially physical chemistry, chemical engineering and mechanical
Laws of Thermodynamics
define fundamental physical
quantities (temperature, energy, and entropy) that characterize
thermodynamic systems at thermal equilibrium. The laws describe how
these quantities behave under various circumstances, and forbid certain
phenomena (such as perpetual motion
Second Law of Thermodynamics
"what goes up must come down"
Second Law of Thermodynamics
dictates that everything ages, Death
decays, and states that the total entropy
isolated system always increases over time
, or remains constant in ideal
cases where the system is in a steady state
or undergoing a reversible
process. The increase in entropy accounts for the irreversibility of
natural processes, and the asymmetry between future and past
Historically, the second law was an empirical finding that was accepted
as an axiom of thermodynamic theory. Statistical thermodynamics,
classical or quantum, explains the microscopic origin of the law. The
second law has been expressed in many ways. There is an upper limit to
the efficiency of conversion of heat to work
in a heat engine
is a branch of science concerned with heat and
temperature and their relation to energy
is an axiomatic concept of thermodynamics.
It is an internal state of a single thermodynamic system, or a relation
between several thermodynamic systems connected by more or less
permeable or impermeable walls. In thermodynamic equilibrium there are
no net macroscopic flows of matter or of energy, either within a system
or between systems. In a system in its own state of internal
, no macroscopic
change occurs. Systems in mutual thermodynamic equilibrium are
simultaneously in mutual thermal, mechanical, chemical, and radiative
equilibria. Systems can be in one kind of mutual equilibrium, though not
in others. In thermodynamic equilibrium, all kinds of equilibrium hold
at once and indefinitely, until disturbed by a thermodynamic operation.
In a macroscopic equilibrium, almost or perfectly exactly balanced
microscopic exchanges occur; this is the physical explanation of the
notion of macroscopic equilibrium.
deals with physical systems that are
not in thermodynamic equilibrium but can adequately be described in terms
of variables (non-equilibrium state variables) that represent an
extrapolation of the variables used to specify the system in
thermodynamic equilibrium. Non-equilibrium thermodynamics is concerned
with transport processes and with the rates of chemical reactions. It
relies on what may be thought of as more or less nearness to
thermodynamic equilibrium. Non-equilibrium thermodynamics is a work in
progress, not an established edifice. This article will try to sketch
some approaches to it and some concepts important for it. Almost all
are not in thermodynamic
equilibrium; for they are changing or can be triggered to change over
time, and are continuously and discontinuously subject to flux of
to and from other systems and to chemical reactions. Some systems and
processes are, however, in a useful sense, near enough to thermodynamic
equilibrium to allow description with useful accuracy by currently known
non-equilibrium thermodynamics. Nevertheless, many natural systems and
processes will always remain far beyond the scope of non-equilibrium
thermodynamic methods. This is because of the very small size of atoms,
as compared with macroscopic systems.
is the material and radiative content of a
macroscopic volume in space, that can be adequately described by
thermodynamic state variables such as temperature, entropy, internal
energy and pressure.
is the study of the interrelation of
heat and work with chemical reactions or with physical changes of state
within the confines of the laws of thermodynamics.
an organic compound with the chemical formula CO(NH2)2. Urea serves an
important role in the metabolism of nitrogen-containing compounds by
animals, and is the main nitrogen-containing substance in the urine of
Thermodynamics of Computation
Chemical Process Modeling
is a computer modeling technique
used in chemical engineering process design. It typically involves using
purpose-built software to define a system of interconnected components,
which are then solved so that the steady-state or dynamic behavior of
the system can be predicted. The system components and connections are
represented as a Process Flow diagram. Simulations can be as simple as
the mixing of two substances in a tank, or as complex as an entire
of a substance is the temperature and pressure
at which the three phases (gas, liquid, and solid) of that substance
coexist in thermodynamic equilibrium.
Thermal energy is the total
energy an object has due to the internal motions of its particles
is related to the average
—not the total
kinetic energy. Put a piece of cold pizza on top of a sheet of aluminum
foil and then stick it in the oven to heat up. After about 10 minutes,
the pizza should be nice and hot—the aluminum foil is the approximately
the same temperature. You can pull the aluminum foil out with your
fingers, but not the pizza. Although the aluminum foil has a high
temperature, its low mass means it doesn't have much thermal energy.
Without a lot of thermal energy in the foil, your
fingers won't get
burned. Meaning? Thermal energy and temperature are different things.
is a column of rising
in the lower
altitudes of Earth's atmosphere
Thermals are created by the uneven heating of Earth's surface from
, and are an example of
. The Sun warms the ground, which in turn
warms the air directly above it. Dark earth, urban areas, and roadways
are good sources of thermals.
objective comparative measurement of
or cold. It is measured by a
thermometer. Several scales and units exist for measuring temperature,
the most common being Celsius (denoted °C; formerly called centigrade),
Fahrenheit (denoted °F), and, especially in science, Kelvin (denoted K).
The coldest theoretical temperature is absolute zero, at which the
thermal motion of atoms and molecules reaches its minimum – classically,
this would be a state of motionlessness, but quantum uncertainty dictates
that the particles still possess a finite zero-point energy
zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius
scale, and −459.67 °F on the Fahrenheit scale. The kinetic theory offers
a valuable but limited account of the behavior of the materials of
macroscopic bodies, especially of fluids. It indicates the absolute
temperature as proportional to the average kinetic energy
of the random
microscopic motions of those of their constituent microscopic particles,
such as electrons, atoms, and molecules, that move freely within the
material. Thermal vibration of a segment of protein alpha helix: The
amplitude of the vibrations increases with temperature. Temperature is
important in all fields of natural science including physics, geology,
chemistry, atmospheric sciences, medicine and biology as well as most
aspects of daily life.
is used in several scales of temperature. The
symbol ° is usually used, followed by the initial letter of the unit, for
example “°C” for degree(s) Celsius. A degree can be defined as a set
change in temperature measured against a given scale, for example, one
degree Celsius is one hundredth of the temperature change between the
point at which water starts to change state from solid to liquid state
and the point at which it starts to change from its gaseous state to
, the zero value is at the freezing
of water and the 100 value is at the Boiling Point
which depends on atmospheric conditions.
freezes into ice is defined as 32 °F, and the boiling point of water is
defined to be 212 °F, a 180 °F separation, as defined at sea level and
standard atmospheric pressure.
is the presence of
low temperature, especially in the atmosphere
. In common usage, cold is
often a subjective perception. A lower bound to temperature is absolute
zero, defined as 0.00 K on the Kelvin scale, an absolute thermodynamic
temperature scale. This corresponds to −273.15 °C on the Celsius scale,
−459.67 °F on the Fahrenheit scale, and 0.00 °R on the Rankine scale.
Since temperature relates to the thermal energy
held by an object or a
sample of matter, which is the kinetic energy
of the random
motion of the
constituents of matter, an object will have less thermal energy
when it is colder and more when it is hotter. If it were possible to cool
a system to absolute zero, all motion of the particles in a sample of
matter would cease and they would be at complete rest in this classical
sense. The object would be described as having zero thermal energy.
Microscopically in the description of quantum mechanics, however, matter
still has zero-point energy even at absolute zero, because of the
uncertainty principle. Ice
is the lower limit of the thermodynamic temperature scale, a state at
which the enthalpy and entropy of a cooled ideal gas reaches its minimum
value, taken as 0. The theoretical temperature is determined by
extrapolating the ideal gas law; by international agreement, absolute
zero is taken as −273.15° on the Celsius scale (International System of
Units), which equates to −459.67° on the Fahrenheit scale (United States
customary units or Imperial units). The corresponding Kelvin and Rankine
temperature scales set their zero points at absolute zero by definition.
is a unit of measure for temperature based upon an absolute scale. It is
one of the seven base units in the International System of Units (SI) and
is assigned the unit symbol K. The Kelvin scale is an absolute,
thermodynamic temperature scale using as its null point absolute zero,
the temperature at which all thermal motion ceases in the classical
description of thermodynamics.
Quantum Super Computer is cooled to 0.01 Kelvin
, which is the coldest
place in the known universe, 100 times colder the space, which is 2.7
kelvins (K) (−270.45 °C; −454.81 °F).
denoted by TP, is the unit of temperature in the system
of natural units known as
. It serves as the defining unit of the
Planck temperature scale
. In this scale the magnitude of the Planck
temperature is equal to 1, while that of absolute zero is 0. Other
temperatures can be converted to Planck temperature units. For example, 0
°C = 273.15 K = 1.9279 × 10−30TP. In SI units, the Planck temperature is
about 1.417×1032 kelvin (equivalently, degrees Celsius, since the
difference is trivially small at this scale), or 2.55×1032 degrees
Fahrenheit or Rankine.
are a set of units of measurement defined exclusively in
terms of five universal physical constants, in such a manner that these
five physical constants take on the numerical value of 1 when expressed
in terms of these units.Body
(0C = 32F, 27C = 80F, for every 10 Degrees F increase is equal
to around a 5C increase)
is a thermodynamic quantity
amount of energy
that is no longer available for
doing mechanical work
available for useful work in a system, and
suggest greater energy
. "entropy increases as matter and energy
in the universe degrade to an ultimate state of
Things must change in Life
. If things
didn't change, there would be no life. Our job as humans is to understand
these changes and react to them accordingly. If things never cooled down,
life could never exist. If things did not
, then new things could not be born.
The Cycle of Life
is something lasting for a very
in statistical thermodynamics, entropy (usual symbol
S) is a measure of the number of microscopic configurations Ω that
correspond to a thermodynamic system in a state specified by certain
. Specifically, assuming that each of the
microscopic configurations is equally probable, the entropy of the
system is the natural logarithm of that number of
multiplied by the Boltzmann constant kB (which provides consistency with
the original thermodynamic concept of entropy discussed below, and gives
entropy the dimension of energy divided by temperature).
Entropy and Life
Entropy and Life
Thermodynamic free energy
is the amount of
that a thermodynamic
system can perform.
Entropy (order disorder)
is associated with the
amount of order, disorder, or
in a thermodynamic system.
is the number of ways we can rearrange the constituents of a system so
that you don't notice
. A low entropy configuration is one in which
there's only a few arrangements that look that way. A high entropy
arrangement is one that there are many arrangements that look that way.
The second law of thermodynamics
-- the law that
says that entropy increases in the universe, or in some isolated bit of
the universe. The reason why entropy increases is simply because there
are many more ways to be high entropy than to be low entropy. Boltzmann
explained that if you start with low entropy, it's very natural for it to
increase because there's more ways to be high entropy. What he didn't
explain was why the entropy was ever low in the first place.
Entropy (information theory
) systems are modeled by a transmitter,
channel, and receiver. The transmitter produces messages that are sent
through the channel. The channel modifies the message in some way. The
receiver attempts to infer which message was sent.
is a force resulting from the entire system's
tendency to increase its entropy, rather than from a
particular underlying microscopic force. For instance, the internal
energy of an ideal gas depends only on its temperature, and not on the
volume of its containing box, so it is not an energy effect that tends to
increase the volume of the box as gas pressure does. This implies that
the pressure of an ideal gas has an entropic origin. What is the origin
of such an entropic force? The most general answer is that the effect of
thermal fluctuations tends to bring a thermodynamic system toward a
macroscopic state that corresponds to a maximum in the number of
microscopic states (or micro-states) that are compatible with this
macroscopic state. In other words, thermal fluctuations tend to bring a
system toward its macroscopic state of maximum entropy.
is a measurement of energy in a thermodynamic system. It is the
thermodynamic quantity equivalent to the total heat content of a system.
It is equal to the internal energy of the system plus the product of
pressure and volume. More technically, it includes the internal energy,
which is the energy required to create a system, and the amount of energy
required to make room for it by displacing its environment and
establishing its volume and pressure.
Janet Iwasa: How 3D Animations help Scientists Visualize what we
is a branch of biology, chemistry, and medicine
(more specifically pharmacology
concerned with the study of the adverse effects of chemicals on living
is the metabolic breakdown of drugs by
is a branch of pharmacology dedicated to
determining the fate of substances administered to a living organism.
is the branch of medicine and biology concerned with the study of drug
action, where a drug can be broadly defined as any man-made, natural, or
endogenous (from within body) molecule which exerts a biochemical and/or
physiological effect on the cell, tissue, organ, or organism (sometimes
the word pharmacon is used as a term to encompass these endogenous and
exogenous bioactive species). More specifically, it is the study of the
interactions that occur between a living organism and chemicals that
affect normal or abnormal biochemical function. If substances have
medicinal properties, they are considered pharmaceuticals.
change of one
substance into another, Transmutation
of metals aimed to purify,
mature, and perfect certain objects.
is a legendary alchemical substance
capable of turning base metals such as mercury into gold.
is a material engineered to have a property that is not found in nature.
They are made from assemblies of multiple elements fashioned from
composite materials such as metals or plastics.
capacities and strength)
Related Pages and Subjects
Chemistry Tools and Equipment
Laboratory Equipment Names and Chemistry Lab Tools
(DIY Citizen Science)
bioengineers develop a 20-cent, hand-powered centrifuge
ultralow-cost paper centrifuge, or paperfuge." With rotational speeds of
up to 125,000 revolutions per minute, the device separates blood plasma
from red cells in 1.5 minutes, no electricity required. A centrifuge is
critical for detecting diseases such as malaria, African sleeping
sickness, HIV and tuberculosis. This low-cost version will enable precise
diagnosis and treatment in the poor, off-the-grid regions where these
diseases are most prevalent.
is a piece of equipment that puts an object in rotation
around a fixed axis (spins it in a circle), applying a potentially strong
force perpendicular to the axis of spin (outward). The centrifuge works
using the sedimentation principle, where the centripetal acceleration
causes denser substances and particles to move outward in the radial
direction. At the same time, objects that are less dense are displaced
and move to the center. In a laboratory centrifuge that uses sample
tubes, the radial acceleration causes denser particles to settle to the
bottom of the tube, while low-density substances rise to the top. There
are 3 types of centrifuge designed for different applications. Industrial
scale centrifuges are commonly used in manufacturing and waste processing
to sediment suspended solids, or to separate immiscible liquids. An
example is the cream separator found in dairies. Very high speed
centrifuges and ultracentrifuges able to provide very high accelerations
can separate fine particles down to the nano-scale
different masses. Large centrifuges are used to simulate high gravity or
acceleration environments (for example, high-G training for test pilots).
Medium-sized centrifuges are used in washing machines and at some
swimming pools to wring water out of fabrics. Gas centrifuges are used
for isotope separation, such as to enrich nuclear fuel for fissile
Chemistry Set History
(wiki)Typical contents found in chemistry sets
Equipment might include: vials
such as copper
nickel or zinc,
metal filings such as
, U-tubes or other reaction vessels,
test tube holders
or other heat source,
Aluminium ammonium sulfate
Ferric ammonium sulfate
The experiments described in the instruction manual typically require a
number of chemicals not shipped with the chemistry set, because they are common
("baker's ammonia" or "salts of hartshorn"),
Other chemicals, including strong acids, bases and oxidizers cannot be safely
shipped with the set and others having a limited shelf life have to be purchased
separately from a
List of Commonly Available Chemicals
is the pursuit of chemistry as a private hobby.
Amateur chemistry is usually done with whatever chemicals are available
at disposal at the privacy of one's home. It should not be confused with
clandestine chemistry, which involves the illicit production of
controlled drugs.[a] Notable amateur chemists include Oliver Sacks and
Sir Edward Elgar.
- Magnetic Constructors
American Chemical Society
American Chemical Society
Industrial & Engineering Chemistry Research
The American Oil
Royal Society of
provides information on the biological activities of small molecules.
Biological properties component database with a
structure similarity search tool.