Front

An atom that has gained or lost electrons is called an ion.

Back

An ion can be either positively charged (cation) or negatively charged (anion).

Front

An atom is stable when its outer energy level is filled with electrons.

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This stability is often achieved through bonding with other atoms.

Front

A chemical formula tells what elements make up a compound and the ratios of the atoms of those elements.

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For example, H2O indicates two hydrogen atoms and one oxygen atom.

Front

A molecule that has a positive end and a negative end is a polar molecule.

Back

Water (H2O) is a common example of a polar molecule.

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A bond that forms between atoms when they share electrons is a covalent bond.

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Covalent bonds are typically found in organic compounds.

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A positive or negative number that is assigned to an element to show its combining ability in a compound is an oxidation number.

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Oxidation numbers help in determining how elements will react.

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A group of atoms with a positive or negative charge is a polyatomic ion.

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Examples include sulfate (SO4^2-) and ammonium (NH4^+).

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A hydrate is a compound that has water chemically attached to its ions.

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For example, CuSO4·5H2O is copper(II) sulfate pentahydrate.

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The force of attraction between the opposite charges of the ions in an ionic compound is an ionic bond.

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Ionic bonds typically form between metals and nonmetals.

Front

Molecules that do not have oppositely charged ends are nonpolar molecules.

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Examples include methane (CH4) and carbon dioxide (CO2).