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Most transition elements have cations of several different charges (see Table 4.2). For
example, iron has the cations Fe2+ and Fe3+.
Table 4.2 Some Common Ions of the Transition Elements: only ions
Ions
Systemic Name
Common Name
Cr3+
Chromium (III)
Chromic
2+
Mn
Manganese (II)
Manganous
Fe2+
Iron (II)
ferrous
3+
Fe
Iron(III)
ferric
2+
Co
Cobalt(II)
cobaltous
Ni2+
Nickel(II)
Cu2+
Copper(II)
Cupric
Ag+
Silver
Zn2+
Zinc
Cd2+
Cadmium
2+
Hg
Mercury(II)
Mercuric
When name a binary compound of a metal and nonmetal
a) The main group metals and nonmetals form ions related to their group number.
b) If an element can form more than one cation, the positive charge of the ion is denoted
by a Roman numeral in parentheses following the element name. Most of transition
metals have cations of several different charges.
In an earlier system of nomenclature, such ions are named by adding suffixes ous and ic
to a stem name of the element to indicate the ions of lower and higher charge,
respectatively. The ending ous is used for lower oxidation state of the metal and ic
ending for the higher oxidation state. You need to know this system of nomenclature
since it is still commonly used.
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2) Binary Compounds of two Nonmetals or metalloids
- Write the element with positive charge first
- Then, write the name of the following element, modified to end in ide
HCl hydrogen chloride
When two elements form more than one compound, we indicate relative number of atoms
through the appropriate prefixes:
Table 1 Greek Prefixes for Naming Compounds______________________
Number
Prefixes
Number
Prefixes
1
mono
6
hexa
2
di
7
hepta
3
tri
8
octa
4
tetra
9
nona
5
penta
10
deca___
Example:
Note: the prefix mono does not used in the first named element.
II. Polyatomic ions
A polyatomic ions is an ion consisting of two or more atoms chemically bonded together
and carrying a net electric charge.
a) Polyatomic anions are more common than polyatomic cations. The most familiar
polyatomic cations are the following:
b) Very few polyatomic anions carry the ide ending in their names.
OH¯ hydroxide ion CN¯ cyanide ion
O22¯ peroxide ion
c) An element common to many polyatomic ions is oxygen, usually in combination with
another nonmetal. Such anions are called oxoanions. Certain nonmetals such as Cl, N, P
and S from a series of oxoanions containing different numbers of oxygen atoms. When
an element has two oxoanions, the name of the one with higher oxidation state (more
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oxygens) ends in –ate; the name of the one with lower oxidation state (less oxygen) ends
in –ite.
When the series of oxoanions of a given element extends to three or four, the prefix hypo
indicates less oxygen and the prefix per indicates more oxygen is used along with the
suffixes ite and ate.
d) Some series of oxoanions also contain varying numbers of H atoms. These ions are
named by prefixing the word hydrogen or dihydrogen as appropriate, to the name of
hydrogen-free anion.
e) All the common oxoanions of Cl, Br, and I carry a charge of 1¯.
f) The prefix thio signifies that a sulfur atom has been substituted for an oxygen atom.
S2O32¯
thiosulfate ion
III. Acids
An acid is a substance that produces one or more hydrogen ions (H+) when dissolved in
water.
a) Binary Acid
Binary acids are certain compounds of H with other nonmetal atoms yield acidic solution
when dissolved in water. In naming acids we use the prefix hydro followed by the name
of the other nonmetal modified with an ic ending.
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b) Oxoacids
An oxoacid is an acid containing hydrogen, oxygen and another element. In water the
oxoacid molecule yields one or more hydrogen ions and an oxoanion. The name of
oxoacid and corresponding oxoanion are related. When the name of anion ends in -ite,
the name of acid ends in -ous. Oxoanions whose names end in ate have associated acids
whose names end in -ic. Prefixes in the name of the oxoanion are retained in the name of
the acid.
Some Oxoacids and Their Corresponding Oxoanions
Oxidation States (O. S.)
~ is related to the number of electrons that an atom loses, gain or otherwise appear to use
in joining with other atoms in compounds.
~ is defined to be the charge an atom in a substance would have if the pairs of electrons
in each bonded belonged to the more electronegative atom.
Whenever two rules appear contradict each other, follow the rule that appears higher on
the list.
1 The oxidation state (number) of an individual atom in a free element is 0.
E.g the O. S. of a Cl atom in Cl2 or an O atom in O2 is zero.
2 The total of the oxidation states of all the atoms in
(a) neutral species, such as isolated atoms, molecules, and formula units, is 0
(b) an ion is equal to the charge on the ion
E.g. the sum of the O. S. of all atoms in MnO4- is –1
3 In their compounds, the group 1 metals have an O.S. of +1 and the group 2 metals have
O.S. of +2.
4 The O.S. of fluorine is –1 in all of its compounds.
5 H has an O.S. 0f +1 in most of its compounds. The exceptions are hydrides, compounds
such as NaH in which H is bonded to metallic elements, where the O. S. of H is –1.
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6 The usual O. S. of oxygen in a compound is –2. The exceptions are peroxides, such as
H2O2 and Na2O2, in which the O. S. of oxygen is –1.
7 In binary compounds with metals, group 17 elements have an O. S. of –1; group 16
E.g. What is the oxidation state of the underlined element in each of the following?
(a) HClO4
(b) MnO4-
(c ) KO2
Formula Mass of Compounds
i) Formula mass
Formula mass(weight): is the mass of a formula unit in atomic mass unit.
Molecular mass: is the mass of a molecule in atomic mass unit.
E.g. Calculate the formula mass (weight) of each of the following