2.5—Molecules and Ions - AP Chemistry - Chemistry - 2011-09-09

2.5—Molecules and Ions

Only 6 noble gases occur in nature as single atoms, so they are called monatomic gases.

molecule is an aggregate of at least two atoms in a definite arrangement held together by chemical forces (also called chemical bonds). Molecules are electrically neutral.

The hydrogen molecule is called a diatomic molecule because it contains only two atoms.

Molecules containing more than two atoms are called polyatomic molecules.

An ion is an atom or a group of atoms that has a net positive or negative charge.

cation, is an ion with a positive charge.

An anion is an ion whose net charge is negative due to an increase in the number of electrons.

An ionic compound is formed from cations and anions.

Monatomic ions contain only one atom. Some examples are Mg2+, Fe3+, S2-, and N3-.

Usually, metals tend to form cations and nonmetals tend to form anions.

Polyatomic ions, such as OH- are ions containing more than one atom.

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