Anion in the context of Polyatomic anion

In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions (cations) and negatively charged ions (anions), which results in a compound with no net electric charge. The constituent ions are held together by electrostatic forces termed ionic bonds.

The component ions in a salt can be either inorganic, such as chloride (Cl), or organic, such as acetate (CH
₃COO
). Each ion can be either monatomic, such as sodium (Na) and chloride (Cl) in sodium chloride, or polyatomic, such as ammonium (NH
₄) and carbonate (CO
₃) ions in ammonium carbonate. Salts containing basic ions hydroxide (OH) or oxide (O) are classified as bases, such as sodium hydroxide and potassium oxide.

Potassium is a chemical element; it has symbol K (from Neo-Latin kalium) and atomic number 19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge (which combines with anions to form salts). In nature, potassium occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in seawater (which is 0.04% potassium by weight), and occurs in many minerals such as orthoclase, a common constituent of granites and other igneous rocks.

Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table. They have a similar first ionization energy, which allows for each atom to give up its sole outer electron. It was first suggested in 1702 that they were distinct elements that combine with the same anions to make similar salts, which was demonstrated in 1807 when elemental potassium was first isolated via electrolysis. Naturally occurring potassium is composed of three isotopes, of which
K is radioactive. Traces of
K are found in all potassium, and it is the most common radioisotope in the human body.

Silicon (/ˈsɪlɪkən/) is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent non-metal (sometimes considered as a metalloid) and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive. Silicon is a significant element that is essential for several physiological and metabolic processes in plants. Silicon is widely regarded as the predominant semiconductor material due to its versatile applications in various electrical devices such as transistors, solar cells, integrated circuits, and others. These may be due to its significant band gap, expansive optical transmission range, extensive absorption spectrum, surface roughening, and effective anti-reflection coating.

Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its oxides form a family of anions known as silicates. Its melting and boiling points of 1414 °C and 3265 °C, respectively, are the second highest among all the metalloids and nonmetals, being surpassed only by boron.

Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply "bicarb", especially in the UK), or salaratus, is a chemical compound with the formula NaHCO₃. It is a salt composed of a sodium cation (Na) and a bicarbonate anion (HCO−3). Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of sodium carbonate ("washing soda"). The natural mineral form is nahcolite, although it is more commonly found as a component of the mineral trona.

As it has long been known and widely used, the salt has many different names such as baking soda, bread soda, cooking soda, brewing soda and bicarbonate of soda and can often be found near baking powder in stores. The term baking soda is more common in the United States, while bicarbonate of soda is more common in Australia, the United Kingdom, and New Zealand. Abbreviated colloquial forms such as sodium bicarb, bicarb soda, bicarbonate, and bicarb are common.

A polyatomic ion (also known as a molecular ion) is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that usually has a net charge that is not zero, or in special case of zwitterion where spatially separated charges where the net charge may be variable depending on acidity conditions. The term molecule may or may not be used to refer to a polyatomic ion, depending on the definition used. The prefix poly- carries the meaning "many" in Greek, but even ions of two atoms are commonly described as polyatomic. There may be more than one atom in the structure that has non-zero charge, therefore the net charge of the structure may have a cationic (positive) or anionic nature depending on those atomic details.

In older literature, a polyatomic ion may instead be referred to as a radical (or less commonly, as a radical group). In contemporary usage, the term radical refers to various free radicals, which are species that have an unpaired electron and need not be charged.

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds. It is one of the main types of bonding, along with covalent bonding and metallic bonding. Ions are atoms (or groups of atoms) with an electrostatic charge. Atoms that gain electrons make negatively charged ions (called anions). Atoms that lose electrons make positively charged ions (called cations). This transfer of electrons is known as electrovalence in contrast to covalence. In the simplest case, the cation is a metal atom and the anion is a nonmetal atom, but these ions can be more complex, e.g. polyatomic ions like NH
₄ or SO
₄. In simpler words, an ionic bond results from the transfer of electrons from a metal to a non-metal to obtain a full valence shell for both atoms.

Clean ionic bonding – in which one atom or molecule completely transfers an electron to another – cannot exist: all ionic compounds have some degree of covalent bonding or electron sharing. Thus, the term "ionic bonding" is given when the ionic character is greater than the covalent character – that is, a bond in which there is a large difference in electronegativity between the cation and anion, causing the bonding to be more polar (ionic) than in covalent bonding where electrons are shared more equally. Bonds with partially ionic and partially covalent characters are called polar covalent bonds.

Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H, and an anion, A. The dissociation or ionization of a strong acid in solution is effectively complete, except in its most concentrated solutions.

Examples of strong acids are hydrochloric acid (HCl), perchloric acid (HClO₄), nitric acid (HNO₃) and sulfuric acid (H₂SO₄).

The term chloride refers to a compound or molecule that contains either a chlorine anion (Cl), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (−Cl). The pronunciation of the word "chloride" is /ˈklɔːraɪd/.

Chloride salts such as sodium chloride are often soluble in water. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating liquid flow in and out of cells. Other examples of ionic chlorides include potassium chloride (KCl), calcium chloride (CaCl₂), and ammonium chloride (NH₄Cl). Examples of covalent chlorides include methyl chloride (CH₃Cl), carbon tetrachloride (CCl₄), sulfuryl chloride (SO₂Cl₂), and monochloramine (NH₂Cl).

In chemistry, iron(III) or ferric refers to the element iron in its +3 oxidation state. Ferric chloride is an alternative name for iron(III) chloride (FeCl₃). The adjective ferrous is used instead for iron(II) salts, containing the cation Fe. The word ferric is derived from the Latin word ferrum, meaning "iron".

Although often abbreviated as Fe, that naked ion does not exist except under extreme conditions. Iron(III) centres are found in many compounds and coordination complexes, where Fe(III) is bonded to several ligands. A molecular ferric complex is the anion ferrioxalate, [Fe(C₂O₄)₃], with three bidentate oxalate ions surrounding the Fe core. Relative to lower oxidation states, ferric is less common in organoiron chemistry, but the ferrocenium cation [Fe(C₅H₅)₂] is well known.

Phosphate minerals are minerals that contain the tetrahedrally coordinated phosphate (PO3−4) anion, sometimes with arsenate (AsO3−4) and vanadate (VO3−4) substitutions, along with chloride (Cl), fluoride (F), and hydroxide (OH) anions, that also fit into the crystal structure.

The phosphate class of minerals is a large and diverse group, however, only a few species are relatively common.

In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula HCO−3.

Bicarbonate serves a crucial biochemical role in the physiological pH buffering system.

An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called an anion) typically found in aqueous solution and written with the chemical formula C
₂H
₃O
₂. The neutral molecules formed by the combination of the acetate ion and a positive ion (called a cation) are also commonly called "acetates" (hence, acetate of lead, acetate of aluminium, etc.). The simplest of these is hydrogen acetate (called acetic acid) with corresponding salts, esters, and the polyatomic anion CH
₃CO
₂, or CH
₃COO
.

Most of the approximately 5 million tonnes of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In nature, acetate is the most common building block for biosynthesis.

Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na and hydroxide anions OH.

Sodium hydroxide is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures, and may cause severe chemical burns at high concentrations. It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air. It forms a series of hydrates NaOH·nH₂O. The monohydrate NaOH·H₂O crystallizes from water solutions between 12.3 and 61.8 °C. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of the anhydrous compound.

The sulfide minerals are a class of minerals containing sulfide (S) or disulfide (S2−2) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts. Sulfide minerals are inorganic compounds.

Aluminosilicate refers to materials containing anionic Si-O-Al linkages. Commonly, the associate cations are sodium (Na), potassium (K) and protons (H). Such materials occur as minerals, coal combustion products and as synthetic materials, often in the form of zeolites. Both synthetic and natural aluminosilicates are of technical significance as structural materials, catalysts, and reagents.

The oxide mineral class includes those minerals in which the oxide anion (O) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. Minerals with complex anion groups such as the silicates, sulfates, carbonates and phosphates are classed separately.