State the valency of A) Sulphite B) Nitrate C) Hydroxide

Answer: The valency of sulphite (SO₃²⁻) is 2, of nitrate (NO₃⁻) is 1, and that of hydroxide (OH⁻) is 1.

Valency means the ability of an element or ion to combine with other atoms. It shows how many bonds it can make. To find the valency of an element, we look at the number of electrons in its outer shell. If there are 1 to 4 electrons, valency is the same number. If there are 5 to 7 electrons, subtract that number from 8 to get the valency. For ions, the valency is equal to the charge (just the number, not the sign).

Complete Answer:

Valency is the ability of an atom or ion to combine with other atoms or ions. It shows how many electrons an atom can lose, gain, or share to achieve a stable electron configuration, usually like that of noble gases. This stable arrangement often involves having eight electrons in the outermost shell – a rule known as the octet rule.

Atoms with fewer than eight electrons in their outer shell tend to either lose, gain, or share electrons to complete the octet, and the number of these electrons involved gives us the valency.

How Do We Find Valency?

• If the number of valence electrons (electrons in the outermost shell) is 1 to 4, then valency = number of valence electrons.
• If the valence electrons are more than 4 (i.e. 5, 6, or 7), then valency = 8 − number of valence electrons.
• For polyatomic ions or radicals, valency equals the combining capacity based on the overall structure or charge.

Let us find the valency of Sulphite, Nitrate, Hydroxide

1. Sulphite

• Chemical Formula: SO₃²⁻
• Atomic Number of Sulphur (S): 16
• Electronic Configuration of Sulphur: 2, 8, 6
• Valence Electrons in Sulphur: 6
• According to the octet rule, sulphur needs 2 more electrons to complete 8 in its outer shell (8 − 6 = 2).

In the structure of the sulphite ion, sulphur forms bonds with three oxygen atoms. Two of these are single bonds, and one is a double bond. This arrangement, along with two extra electrons (shown as a -2 charge), allows the sulphite ion to behave as if it needs 2 positive charges to balance. Therefore, valency of sulphite is 2.

2. Nitrate

• Chemical Formula: NO₃⁻
• Atomic Number of Nitrogen (N): 7
• Electronic Configuration: 2, 5
• Valence Electrons in Nitrogen: 5
• According to the octet rule, nitrogen requires 3 more electrons to complete its outer shell (8 − 5 = 3).

In the structure of the nitrate ion, nitrogen is bonded with three oxygen atoms — one double bond and two single bonds (with one of the oxygen atoms carrying a negative charge). Despite nitrogen needing 3 electrons, the entire NO₃ molecule carries a -1 charge, which determines its combining capacity. Therefore, valency of nitrate is 1.

3. Hydroxide

• Chemical Formula: OH⁻
• Atomic Number of Oxygen (O): 8
• Electronic Configuration of Oxygen: 2, 6
• Valence Electrons in Oxygen: 6
• Oxygen needs 2 more electrons to complete its outer shell (8 − 6 = 2).

In the hydroxide ion, one of these electrons is provided by the hydrogen atom it bonds with. The extra negative charge indicates the presence of one more electron, so only one more positive charge is needed to neutralize it. Therefore, valency of hydroxide is 1.

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