Question

Write the valency number of the following elements – Magnesium, Silicon, Krypton and Sulphur.

Answer 1

Hint: Valency of an element refers to the number of electrons it requires to achieve its stable most configuration. An atom, element or a compound has a tendency to exist in its most stable form. This is the sole reason why reactions occur.

Complete step by step answer:
Let us understand the concept of valency first. The valence or valency of an element is defined as “a measure of its combining power with other atoms when it forms chemical compounds or molecules”.
In simpler words, valency is the number of electrons an element loses or gains. Let us look at the simple electronic configuration of the given elements.
Magnesium (Atomic number - 12)
Electronic configuration – 2, 8, 2
Valency = 2
Silicon (Atomic number - 14)
Electronic configuration - 2, 8, 4
Valency = 4
Krypton (Atomic number - 36)
Electronic configuration – 2, 8, 18, 8
Valency = 0
Sulphur (Atomic number - 16)
Electronic configuration - 2, 8, 6
Valency = 2
Therefore, the answer is – The valency number of the following elements is –
Magnesium = 2
Silicon = 4
Krypton = 0
Sulphur = 2

Additional Information:
You can also remember valency as –
Valency of metal(If number of valence shell electron is less than 4) = number of valence electrons
Valency of a non-metal(If number of valence shell electron is more than 4) = 8 – number of valence electrons

Note: Let us discuss more about given elements.
Magnesium can lose two electrons to have the same configuration as that of Neon.
Silicon can form up to four bonds and achieve a stable configuration.
Krypton has a stable octet. Therefore, it neither gains or loses electrons.
Sulphur shows multiple valencies, it is because it has more orbitals.
Sulphur can gain 2 electrons to complete its octet
Sulphur can also lose 6 electrons
Other than this, Sulphur can show more valencies depending on the compound it forms a bond with.