Chemical substance

Steam and liquid water are two different forms of the same chemical (pure) substance: water.
Colors of a single chemical (Nile red) in different solvents, under visible and UV light, showing how the chemical interacts dynamically with its solvent environment.
Native sulfur crystals. Sulfur occurs naturally as elemental sulfur, in sulfide and sulfate minerals and in hydrogen sulfide.
Potassium ferricyanide is a compound of potassium, iron, carbon and nitrogen; although it contains cyanide anions, it does not release them and is nontoxic.
Cranberry glass, while appearing homogeneous, is a mixture consisting of glass and gold colloidal particles of about 40nm in diameter, giving it a red color.
Chemicals in graduated cylinders and beaker.

Form of matter having constant chemical composition and characteristic properties.

- Chemical substance
Steam and liquid water are two different forms of the same chemical (pure) substance: water.

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A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.

Chemical reaction

A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.
Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen.
As seen from the equation CH4 + 2O2 -> CO2 + 2 H2O, a coefficient of 2 must be placed before the oxygen gas on the reactants side and before the water on the products side in order for, as per the law of conservation of mass, the quantity of each element does not change during the reaction
An example of organic reaction: oxidation of ketones to esters with a peroxycarboxylic acid
Isomerization of azobenzene, induced by light (hν) or heat (Δ)
Representation of four basic chemical reactions types: synthesis, decomposition, single replacement and double replacement.
Illustration of a redox reaction
Sodium chloride is formed through the redox reaction of sodium metal and chlorine gas
Ferrocene – an iron atom sandwiched between two C5H5 ligands
Precipitation
In this Paterno–Büchi reaction, a photoexcited carbonyl group is added to an unexcited olefin, yielding an oxetane.
Schematic potential energy diagram showing the effect of a catalyst in an endothermic chemical reaction. The presence of a catalyst opens a different reaction pathway (in red) with a lower activation energy. The final result and the overall thermodynamics are the same.
Solid heterogeneous catalysts are plated on meshes in ceramic catalytic converters in order to maximize their surface area. This exhaust converter is from a Peugeot 106 S2 1100
Mechanism of electrophilic aromatic substitution
E2 elimination
Electrophilic addition of hydrogen bromide
Acid-catalyzed addition-elimination mechanism
The Cope rearrangement of 3-methyl-1,5-hexadiene
Illustration of the induced fit model of enzyme activity
Thermite reaction proceeding in railway welding. Shortly after this, the liquid iron flows into the mould around the rail gap.

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.

Heat of vaporization of water from melting to critical temperature

Properties of water

Polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue.

Polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue.

Heat of vaporization of water from melting to critical temperature
Density of ice and water as a function of temperature
Temperature distribution in a lake in summer and winter
WOA surface density
Red line shows saturation
Vapor pressure diagrams of water
The solid/liquid/vapour triple point of liquid water, ice Ih and water vapor in the lower left portion of a water phase diagram.
A diagram showing the partial charges on the atoms in a water molecule
Dew drops adhering to a spider web
Rain water flux from a canopy. Among the forces that govern drop formation: Surface tension, Cohesion (chemistry), Van der Waals force, Plateau–Rayleigh instability.
This paper clip is under the water level, which has risen gently and smoothly. Surface tension prevents the clip from submerging and the water from overflowing the glass edges.
Temperature dependence of the surface tension of pure water
Presence of colloidal calcium carbonate from high concentrations of dissolved lime turns the water of Havasu Falls turquoise.
Model of hydrogen bonds (1) between molecules of water
Some hydrogen-bonding contacts in FeSO4.7H2O. This metal aquo complex crystallizes with one molecule of "lattice" water, which interacts with the sulfate and with the [Fe(H2O)6]2+ centers.

Water is the chemical substance with chemical formula ; one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom.

A diagram representing at the microscopic level the differences between homogeneous mixtures, heterogeneous mixtures, compounds, and elements

Mixture

Material made up of two or more different chemical substances which are not chemically bonded.

Material made up of two or more different chemical substances which are not chemically bonded.

A diagram representing at the microscopic level the differences between homogeneous mixtures, heterogeneous mixtures, compounds, and elements

Chemical substance

Steam and liquid water are two different forms of the same chemical (pure) substance: water.

Chemical compound

Steam and liquid water are two different forms of the same chemical (pure) substance: water.

A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) composed of atoms from more than one element held together by chemical bonds.

Appearance of real linear polymer chains as recorded using an atomic force microscope on a surface, under liquid medium. Chain contour length for this polymer is ~204 nm; thickness is ~0.4 nm.

Polymer

A polymer ( Greek poly-, "many" + -mer, "part")

A polymer ( Greek poly-, "many" + -mer, "part")

Appearance of real linear polymer chains as recorded using an atomic force microscope on a surface, under liquid medium. Chain contour length for this polymer is ~204 nm; thickness is ~0.4 nm.
Cartoon schematic of polymer molecules
Structure of a styrene-butadiene chain, from a molecular simulation.
Some memorable milestones in the history of polymers
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Microstructure of part of a DNA double helix biopolymer
Branch point in a polymer
A polyethylene sample that has necked under tension.
Thermal transitions in (A) amorphous and (B) semicrystalline polymers, represented as traces from differential scanning calorimetry. As the temperature increases, both amorphous and semicrystalline polymers go through the glass transition (Tg). Amorphous polymers (A) do not exhibit other phase transitions, though semicrystalline polymers (B) undergo crystallization and melting (at temperatures Tc and Tm, respectively).
Phase diagram of the typical mixing behavior of weakly interacting polymer solutions, showing spinodal curves and binodal coexistence curves.
A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration, swelling, and crazing of the material
Chlorine attack of acetal resin plumbing joint
Ozone-induced cracking in natural rubber tubing

is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits.

The chemical elements ordered in the periodic table

Chemical element

The chemical elements ordered in the periodic table
Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements.
Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the alpha process. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the r-process. Certain large stars slowly produce other elements heavier than iron, in the s-process; these may then be blown into space in the off-gassing of planetary nebulae
Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the Oddo-Harkins rule), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae.
Mendeleev's 1869 periodic table: An experiment on a system of elements. Based on their atomic weights and chemical similarities.
Dmitri Mendeleev
Henry Moseley

A chemical element refers to all aspects of the species of atoms that have a certain number of protons in their nuclei, including the pure substance consisting only of that species.

The chemical elements ordered in the periodic table

Chemical composition

Chemical composition refers to identity and number of the chemical elements that make up any particular compound.

Chemical composition refers to identity and number of the chemical elements that make up any particular compound.

The chemical elements ordered in the periodic table

The chemical composition of a pure substance corresponds to the relative amounts of the elements that constitute the substance itself.

REACh Key Dates

Registration, Evaluation, Authorisation and Restriction of Chemicals

European Union regulation dating from 18 December 2006.

European Union regulation dating from 18 December 2006.

REACh Key Dates

REACH addresses the production and use of chemical substances, and their potential impacts on both human health and the environment.

An oil painting of a chemist (Ana Kansky, painted by Henrika Šantel in 1932)

Chemistry

Scientific study of the properties and behavior of matter.

Scientific study of the properties and behavior of matter.

An oil painting of a chemist (Ana Kansky, painted by Henrika Šantel in 1932)
Laboratory, Institute of Biochemistry, University of Cologne in Germany.
Solutions of substances in reagent bottles, including ammonium hydroxide and nitric acid, illuminated in different colors
A diagram of an atom based on the Bohr model
Standard form of the periodic table of chemical elements. The colors represent different categories of elements
Carbon dioxide (CO2), an example of a chemical compound
A ball-and-stick representation of the caffeine molecule (C8H10N4O2).
A 2-D structural formula of a benzene molecule (C6H6)
Diagram showing relationships among the phases and the terms used to describe phase changes.
An animation of the process of ionic bonding between sodium (Na) and chlorine (Cl) to form sodium chloride, or common table salt. Ionic bonding involves one atom taking valence electrons from another (as opposed to sharing, which occurs in covalent bonding)
In the methane molecule (CH4), the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms. Thus, the octet rule is satisfied for C-atom (it has eight electrons in its valence shell) and the duet rule is satisfied for the H-atoms (they have two electrons in their valence shells).
Emission spectrum of iron
During chemical reactions, bonds between atoms break and form, resulting in different substances with different properties. In a blast furnace, iron oxide, a compound, reacts with carbon monoxide to form iron, one of the chemical elements, and carbon dioxide.
The crystal lattice structure of potassium chloride (KCl), a salt which is formed due to the attraction of K+ cations and Cl− anions. Note how the overall charge of the ionic compound is zero.
Hydrogen bromide exists in the gas phase as a diatomic molecule
Democritus' atomist philosophy was later adopted by Epicurus (341–270 BCE).
15th-century artistic impression of Jābir ibn Hayyān (Geber), a Perso-Arab alchemist and pioneer in organic chemistry.
Antoine-Laurent de Lavoisier is considered the "Father of Modern Chemistry".
In his periodic table, Dmitri Mendeleev predicted the existence of 7 new elements, and placed all 60 elements known at the time in their correct places.
Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. 
Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated charge.

It is a natural science that covers the elements that make up matter to the compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.

Example for a dissolved solid (left)

Solubility

Example for a dissolved solid (left)
Formation of crystals in a 4.2 M ammonium sulfate solution. The solution was initially prepared at 20 °C and then stored for 2 days at 4 °C.
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Dissolution of sodium chloride in water
Thermodynamic cycle for calculating solvation via sublimation
Thermodynamic cycle for calculating solvation via fusion

In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent.