Basics ‹ 59
column of the periodic table and decrease by 1 as you move to the left on the periodic table.
Metalloids may be treated as metals or nonmetals. Examples are:
Na+ Al^3 + Pb^4 + N^3 - Se^2 - I-
Na+ Mg^2 + Al^3 + Si^4 + P3– S2– Cl– Ar^0Transition Metals
Many transition metals and the group of six elements centered around lead on the periodic
table commonly have more than one valence. The valence of these metals in a compound
must be known before the compound can be named. Modern nomenclature rules indicate
the valence of one of these metals with a Roman numeral suffix (Stock notation). Older
nomenclature rules used different suffixes to indicate the charge. Examples:
- FeCl 3
Fe^3 +Cl 31 - (crisscross rule)
The compound is named iron(III) chloride or ferric chloride.
- FeCl 2
If chloride is -1, two chloride ions are -2. Fe has a valence of +2, to give a total charge
of zero. The name is iron(II) chloride or ferrous chloride.
- MnO 2
Mn^4 + (found previously)
The name would be manganese(IV) oxide, although it is often named manganese dioxide.
The Roman numeral suffix is part of the name of the metal. Thus iron(III) is one word.
Stock notation should be used for all metals that have a variable valence. This includes
almost all the transition elements and the elements immediately around lead on the periodic
table. Stock notation is often omitted for Zn, Cd, and Ag, as they do not have variable valences.
The valences of some common metals and acids are listed in the appendixes.
Coordination Compounds
Coordination compounds contain a complex. In general, a complex may be recognized
because it is enclosed in square brackets [ ]. The square brackets are omitted when the actual
structure of the complex is uncertain.
A complex is composed of a central atom, normally a metal, surrounded by atoms or
groups of atoms called ligands. One way of forming a complex is illustrated below:
Ni^2 + + 6 H 2 O → [Ni(H 2 O) 6 ]^2 +
In this reaction, the metal behaves as a Lewis acid and accepts a pair of electrons from
the Lewis base (ligand). In this case, the ligand is water, with the oxygen atom donating one
of its lone pairs to the nickel. The oxygen atom is called the donor atom. In this complex,
there are six donor atoms.
A complex may be ionic or neutral. An ionic complex is called a complex ion.
A neutral complex is a type of coordination compound. The only difference in naming
coordination compounds or complex ions is that anionic complex ions have an ate suffix.
A coordination compound may contain more than one complex ion or material that is
not part of the complex, but it must have an overall neutral charge. Examples of coordination
compounds are: [Pt(NH 3 ) 2 Cl 2 ], K 2 [Mn(C 2 O 4 ) 3 ], and [Ni(H 2 O) 6 ]SO 4.
When writing formulas, the metal (central atom) is always listed first within the brackets.
However, when writing names, the metal name is always given last. Any material not listed
within the brackets is named separately.