Names and Formulas of Compounds

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Ion Noun

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[ahy-on]

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Ion

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An atom or group of atoms that has a net positive or negative charge due to losing or gaining electrons.

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Example: An ionic compound, made of positive cations and negative anions, dissolves as polar water molecules surround and separate the individual ions.

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Monoatomic Ion Noun

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[mon-oh-uh-tom-ik ahy-on]

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Monoatomic Ion

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An ion consisting of a single atom that has acquired a positive or negative charge by losing or gaining electrons.

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Example: A neutral sodium atom (Na) with an equal number of protons and electrons becomes a positively charged monoatomic ion (Na+) when it loses one electron.

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Cation Noun

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[kat-ahy-on]

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Cation

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An ion with a net positive charge, which is formed when a neutral atom loses one or more electrons.

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Example: A neutral sodium (Na) atom loses an electron from its outer shell, resulting in a positively charged ion called a cation (Na+).

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Anion Noun

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[an-ahy-on]

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Anion

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An ion with a net negative charge, which is formed when a neutral atom gains one or more electrons.

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Example: A neutral chlorine atom gains an electron, filling its outer shell and becoming a negatively charged chloride ion, which is an anion.

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Stock System Noun

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[stok sis-tuhm]

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Stock System

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A chemical naming method where a Roman numeral in parentheses indicates the oxidation state or charge of a cation.

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Example: The image shows how the Stock System uses Roman numerals, like (II) and (III), to give unique names to different compounds made from the same elements.

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Polyatomic Ion Noun

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[pol-ee-uh-tom-ik ahy-on]

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Polyatomic Ion

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A charged chemical species composed of two or more atoms covalently bonded together that acts as a single unit.

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Example: This image shows that a polyatomic ion is a group of atoms bonded together that has an overall positive or negative charge.

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Chemical Formula Noun

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[kem-i-kuhl fawr-myuh-luh]

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Chemical Formula

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A representation of a substance using chemical symbols for elements and subscripts to show the number of atoms of each.

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Example: The chemical formula CO₂ shows that one carbon atom (C) is bonded to two oxygen atoms (O) to form a carbon dioxide molecule.

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Binary Compound Noun

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[bahy-nuh-ree kom-pound]

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Binary Compound

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A chemical compound that is composed of exactly two different elements, which can be bonded ionically or covalently.

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Example: This diagram shows that water (H₂O) is a binary compound because it is made of exactly two different elements: Hydrogen (H) and Oxygen (O).

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Crisscross Method Noun

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[kris-kros meth-uhd]

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Crisscross Method

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A technique for writing an ionic compound's formula by making the charge of each ion the subscript for the other.

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Example: This diagram shows how the charge number of one ion (like Mg²⁺) becomes the subscript for the other ion (Br), and vice-versa, to create the final chemical formula (MgBr₂).

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Subscript Noun

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[suhb-skript]

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Subscript

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A number written to the lower right of a chemical symbol indicating the number of atoms of that element.

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Example: In the chemical formula for methane, CH₄, the subscript '4' indicates there are four hydrogen (H) atoms bonded to one carbon (C) atom.