Empirical formula in the context of Sodium hydride

A chemical formula is a 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. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name since it does not contain any words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. 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.

The simplest types of chemical formulae are called empirical formulae, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulae indicate the simple numbers of each type of atom in a molecule, with no information on structure. For example, the empirical formula for glucose is CH₂O (twice as many hydrogen atoms as carbon and oxygen), while its molecular formula is C₆H₁₂O₆ (12 hydrogen atoms, six carbon and oxygen atoms).

A carbohydrate (/ˌkɑːrboʊˈhaɪdreɪt/) is a sugar (saccharide) or a sugar derivative. For the simplest carbohydrates, the carbon-to-hydrogen-to-oxygen atomic ratio is 1:2:1, i.e. they are often represented by the empirical formula C(H₂O)_n. Together with amino acids, fats, and nucleic acids, the carbohydrates are one of the major families of biomolecules.

Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as an energy store (e.g., starch and glycogen) and as structural components (e.g., cellulose in plants and chitin in arthropods and fungi). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g., ATP, FAD and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides and their derivatives play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.

Zircon (/ˈzɜːrkɒn, -kən/) is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is ZrSiO₄. An empirical formula showing some of the range of substitution in zircon is (Zr_1–y, REE_y)(SiO₄)_1–x(OH)_4x–y. Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.

The name derives from the Persian zargun, meaning "gold-hued". This word is changed into "jargoon", a term applied to light-colored zircons. The English word "zircon" is derived from Zirkon, which is the German adaptation of this word. Yellow, orange, and red zircon is also known as "hyacinth", from the flower hyacinthus, whose name is of Ancient Greek origin.

The sulfate or sulphate ion is a polyatomic anion with the empirical formula SO₄. Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many are prepared from that acid.

A chemical composition specifies the identity, arrangement, and ratio of the chemical elements making up a compound by way of chemical and atomic bonds.

Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for water is H₂O: this means that each molecule of water is constituted by 2 atoms of hydrogen (H) and 1 atom of oxygen (O). The chemical composition of water may be interpreted as a 2:1 ratio of hydrogen atoms to oxygen atoms. Different types of chemical formulas are used to convey composition information, such as an empirical or molecular formula.

Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg ions and O ions held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + H₂O → Mg(OH)₂), but it can be reversed by heating it to remove moisture.

Magnesium oxide was historically known as magnesia alba (literally, the white mineral from Magnesia), to differentiate it from magnesia nigra, a black mineral containing what is now known as manganese.

Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); most often, in such materials, some small percentage of atoms are missing or too many atoms are packed into an otherwise perfect lattice work.

Contrary to earlier definitions, modern understanding of non-stoichiometric compounds view them as homogeneous, and not mixtures of stoichiometric chemical compounds. Since the solids are overall electrically neutral, the defect is compensated by a change in the charge of other atoms in the solid, either by changing their oxidation state, or by replacing them with atoms of different elements with a different charge. Many metal oxides and sulfides have non-stoichiometric examples; for example, stoichiometric iron(II) oxide, which is rare, has the formula FeO, whereas the more common material is nonstoichiometric, with the formula Fe_0.95O. The type of equilibrium defects in non-stoichiometric compounds can vary with attendant variation in bulk properties of the material. Non-stoichiometric compounds also exhibit special electrical or chemical properties because of the defects; for example, when atoms are missing, electrons can move through the solid more rapidly. Non-stoichiometric compounds have applications in ceramic and superconductive material and in electrochemical (i.e., battery) system designs.

Porphine or porphin is an organic compound of empirical formula C₂₀H₁₄N₄. It is heterocyclic and aromatic. The molecule is a flat macrocycle, consisting of four pyrrole-like rings joined by four methine bridges, which makes it the simplest of the tetrapyrroles.

The nonpolar tetrapyrrolic ring structure of porphine means it is poorly soluble in most organic solvents and hardly water soluble. As a result, porphine is mostly of theoretical interest. It has been detected in GC-MS of certain fractions of Piper betle.

A fullerene is an allotrope of carbon whose molecules consist of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to six atoms. The molecules may have hollow sphere- and ellipsoid-like forms, tubes, or other shapes.

Fullerenes with a closed mesh topology are informally denoted by their empirical formula C_n, often written Cn, where n is the number of carbon atoms. However, for some values of n there may be more than one isomer.

Phosphorus pentoxide is a chemical compound with molecular formula P₄O₁₀ (with its common name derived from its empirical formula, P₂O₅). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydrating agent.

A carbohydrate (/ˌkɑːrboʊˈhaɪdreɪt/) is a sugar (saccharide) or a sugar derivative. For the simplest carbohydrates, the carbon-to-hydrogen-to-oxygen atomic ratio is 1:2:1, i.e. they are often represented by the empirical formula (CH₂O)_n. Together with amino acids, fats, and nucleic acids, the carbohydrates are one of the major families of biomolecules.

Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as an energy store (e.g., starch and glycogen) and as structural components (e.g., cellulose in plants and chitin in arthropods and fungi). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g., ATP, FAD and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides and their derivatives play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.

Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C₁₅H₂₄. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications such as oxidation or rearrangement produce the related sesquiterpenoids. It is estimated (2006) that 3000 sesquiterpenes have been identified.