Page 1 - 3. LESSON NOTES-(IONSPOSITIVE&NEGATIVE IONSCALCULATION OF VALENCY OF IONS)

SAI International School
Class-IX

Subject- Chemistry
Topic-Atoms and Molecules
Topic-Ions (positive ion and negative ion), calculations of valency

of ions
LESSON NOTE
Ions
The charged particles (atoms) are called ions, they charge or negative charge on
it:
Negatively charged ion is called anion (Cl )
-
Positively charge ion is called cation (Na ).
+
Polyatomic ions: These are the ions which contain atoms of more than one element
which carry a single charge and behave as a single unit in chemical combinations.
Example: NH4 ,SO4
+
2-
• Valency
The combining capacity of an element is known as its valency: Valency is used
to find out how atom of an element will combine with the atom of another element to
form a chemical compound.
(Every atom want, to become stable, to do so it may lose, gain or share
electrons.
(i) If an atom consists of 1, 2 or 3 electrons in its valance shell then its valency is
1, 2 or 3 respectively,
(ii) If an atom consists of 5, 6 or 7 electrons in the outermost shell, then it will
gain 3, 2 or 1 electron respectively and its valency will be 3, 2 or 1 respectively.
(ii) If an atom has 4 electrons in the outermost shell than it will she this electron
and hence its valency will be 4.
(iv) If an atom has 8 electrons in the outermost shell then its valency is 0.
POSITIVE IONS/RADICALS NEGATIVE IONS/RADICALS
VALENCY 1-Monovalent elements VALENCY 1-Monovalent elements
L
ORIDE
1+
CH

POTASSIUM K Cl
1-

1+
1-

T
ORA

L

E
SODIUM Na ClO3
CH

1-
1+
RIT

LITHIUM Li ClO
E
P
HY
OCHLO
1-
1+
HYDROGEN H Br

IDE
ROM
B

1+
1-
AMMONIUM NH4 IODIDE I
1-
HYDROXIDE OH
1-
Variable Valencies NITRITE NO2
1-
Cuprous [Copper [I] ] NITRATE NO3
Cu HYDROGEN [BI] CARBONATE HCO3
1-
1+
1-
Argentous [Silver [I] ] HYDROGEN [BI] SULPHITE HSO3
1-
Ag HYDROGEN [BI] SULPHATE HSO4
1+
1-
Mercurous [Mercury] ] ALUMINATE AlO2
1+
Hg PERMANGANATE MnO4 1-
Aurous [Gold] [I] ]
1+
Au

1