Question

Write the electronic configuration and valency of the following elements.

Element	Atomic Number
Magnesium	12

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 Magnesium 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.
• The 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 Magnesium is 12.
• 2 electrons will fill the first shell i.e., the K shell.
• 8 electrons will fill the second shell i.e., the L shell.
• 2 electrons will enter the third shell i.e., the M shell.
• The electronic configuration of Lithium will be 2,8,2.
• Lithium has 2 electrons in its valence shell to lose and have an octet configuration in its outermost shell.
• Hence, its valency is 2.