Page 18 - Chemistry ICSE Class IX

6 ICSE Chemistry – 9
2+
3+
+
For example, copper exists as Cu and Cu , iron occurs as Fe and
2+
Fe etc. The name of the ion having lower valency number ends with ous,
while that of higher valency ends with ic.
Name of the Constituent Formula of the
Metal Valency
compound metal ion compound
Iron 2 Ferrous oxide Fe 2+ FeO
3 Ferric oxide Fe 3+ Fe O 3
2
Copper 1 Cuprous oxide Cu + Cu O
2
2 Cupric oxide Cu 2+ CuO
According to the modern notation, such ions are described by writing
their valencies in Roman numerals within the parenthesis immediately
after the symbol. For example:
+
Cuprous ion (Cu ) is now written as Cu(I) ion
2+
Cupric ion (Cu ) is now written as Cu(II) ion
2+
Ferrous ion (Fe ) is now written as Fe(II) ion
3+
Ferric ion (Fe ) is now written as Fe(III) ion
Why do certain elements show variable valencies
Certain elements can use electrons both from their valence shell as well as
tŚĞŶ ĂŶ ĂƚŽŵ ůŽƐĞƐ ĞůĞĐƚƌŽŶƐ ĨƌŽŵ
ŝƚƐ ƉĞŶƵůƟŵĂƚĞ ƐŚĞůů ;ŝŶ ĂĚĚŝƟŽŶ ƚŽ from the penultimate shell (the next lower shell to the valency shell). As a
ƚŚĞ ǀĂůĞŶĐĞ ƐŚĞůůͿ͕ ŝƚ ĞdžŚŝďŝƚƐ ǀĂƌŝĂďůĞ result, they are able to show more than one valencies, i.e., they can exhibit
ǀĂůĞŶĐLJ͘ variable valency.

Radicals

What are the radicals

A molecule of any compound consists of two parts – one coming from the
parent acid and the other from the parent base. These parts may contain
single atom or group of atoms.
An atom or a group of atoms of different elements, carrying positive
or negative charge, which exist in a compound is called a radical.
The part of a molecule of any compound coming from the parent acid
is called the acid radical, whereas that coming from the parent base is
called the basic radical.
ƒ The radicals may be made up of one or more atoms. The atoms within
a radical are bonded to each other by covalent bonds. That is why,
each radical behaves as a single unit in all reactions.
dŚĞ ͚ƌĂĚŝĐĂůƐ͛ ĂƌĞ ŶŽǁĂĚĂLJƐ ĐĂůůĞĚ ƒ A radical may carry negative or positive charge.
ƉŽůLJĂƚŽŵŝĐ ŝŽŶƐ͘ The basic radicals carry positive charge, whereas acid radicals carry
ͻ negative charge. Thus,
dŚĞ ƚĞƌŵ ͚ƌĂĚŝĐĂů͛ ŝƐ ŶŽǁ ƵƐĞĚ ŽŶůLJ
ĨŽƌ ĐŚĞŵŝĐĂů ƐƉĞĐŝĞƐ ƚŚĂƚ ĐŽŶƚĂŝŶ ĂŶ Š basic radicals are cations, and
ƵŶƉĂŝƌĞĚ ĞůĞĐƚƌŽŶ͘ Š the acid radicals are anions.
ƒ Each radical retains its identity in chemical reactions.
ƒ Radicals have their own combining capacities. Therefore, radicals
have their characteristic valencies.
For example:
+
+
Basic radicals: Ammonium radical (NH ), Sodium radical (Na ),
4
2–
3–
Acid radicals: Sulphate radical (SO ), Phosphate radical (PO )
4
4
–
2–
Dichromate radical (Cr O ), Chloride radical (Cl )
2
7