Question

Give reasons for the following:

Sulphur exhibits negative valency.

Answer 1

• Valency- Valency is the combining capacity of an atom.
• Valence electrons- The electrons present in the valence shell i.e., the outermost shell of an atom are known as valence electrons.
• Valence electrons take part in the chemical reaction.
• These electrons decide the chemical properties of an atom.
• To know the number of valence electrons in Aluminium we first need to write the electronic configuration of these elements.
• The electronic configuration of an element describes how electrons are distributed in its atomic orbitals.
• The electrons are filled in the increasing number of shells viz. K, L, M, N, etc.
• Number of electrons in a shell is given by 2n² where n is the number of shells.
• Putting n = 1,2,3 and 4, we get the number of electrons 2,8,18, 32 that can be filled in each shell respectively.

Electronic configuration-

• The atomic number of Sulphur is 16.
• 2 electrons will fill the first shell i.e., the K shell.
• 8 electrons will fill the second shell i.e., the L shell.
• 6 electrons will enter the third shell i.e., the M shell.
• The electronic configuration of Sulphur will be 2,8,6.

Negative valency-

• In order to get octet in its valence shell Sulphur has to gain 2 electrons in its valence shell.
• When Sulphur gains 2 electrons in its shell it has now 2 more electrons as compared to the number of protons in its atom.
• Sulphur is a non-metal, and non-metals have the tendency to gain electrons to form negative ions i.e., anions.

Hence, Sulphur has a negative valency.