ATOMS AND ION FORMATION stable atom: unreactive, at rest a state likely to be found in nature has 8 valence e– outer shell e– like a noble gas (8 e– = stable!) opposite = reactive or unstable

VALENCE ELECTRONS number of valence e– = group # Li and Na – 1 valence electron Mg and Ca – O and S –

FORMATION OF IONS Atoms lose or gain e– to achieve a noble gas configuration Once e– are gained/lost, a charge exists (positive or negative) Charged particles are called IONS

POSITIVE IONS: CATIONS formed by metals lose electrons to achieve noble gas configuration charge of the cation = group # example: lithium ion = 1+ aluminum ion = barium ion =

POSITIVE IONS: CATIONS

NEGATIVE IONS: ANIONS formed by nonmetals gain electrons to achieve noble gas configuration charge of the anion = group# – 8 oxide anion = 6 – 8 = 2– N (nitride) anion =

NEGATIVE IONS: ANIONS

ANIONS vs. CATIONS ANIONS end in -ide ex: bromide, oxide, sulfide bromide anion = Br1– oxide anion = O2– always larger than the atom from which it was formed

ANIONS VS. CATIONS CATIONS have the same name as the element ex: sodium cation, Na1+ magnesium ion, Mg2+ always smaller than the atom from which it was formed