Chemical substance and Related Topics

Chemical element

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$Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements.$

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.

A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species.

Chemical compound

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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.

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

Chemical reaction

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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.

Sodium chloride is formed through the redox reaction of sodium metal and chlorine gas

Ferrocene – an iron atom sandwiched between two C5H5 ligands

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

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.

Isobutane structural formula
Molecular formula: C4H10
Condensed or semi-structural chemical formula: (CH3)3CH

Way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus and minus (−) signs.

Traditional formula: MC60 The "@" notation: M@C60

Chemical formulae can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than chemical names and structural formulae.

Molecule

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Group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion.

A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings.

AFM image of 1,5,9-trioxo-13-azatriangulene and its chemical structure.

A covalent bond forming H2 (right) where two hydrogen atoms share the two electrons

Sodium and fluorine undergoing a redox reaction to form sodium fluoride. Sodium loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically.

3D (left and center) and 2D (right) representations of the terpenoid molecule atisane

Structure and STM image of a "cyanostar" dendrimer molecule.

Hydrogen can be removed from individual H2TPP molecules by applying excess voltage to the tip of a scanning tunneling microscope (STM, a); this removal alters the current-voltage (I-V) curves of TPP molecules, measured using the same STM tip, from diode like (red curve in b) to resistor like (green curve). Image (c) shows a row of TPP, H2TPP and TPP molecules. While scanning image (d), excess voltage was applied to H2TPP at the black dot, which instantly removed hydrogen, as shown in the bottom part of (d) and in the rescan image (e). Such manipulations can be used in single-molecule electronics.

Earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.

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

Chemistry

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Scientific study of the properties and behavior of matter.

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).

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.