Question

Elements A, B and C have atomic numbers 9,20 and 10 respectively.

State which one is

(1) a non-metal,

(2) a metal,

(3) chemically inert

Answer 1

• 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 shell.
• 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.

Element A-

• Its atomic number is 9.
• The electronic configuration will be written as 2,7.

Element B-

• Element B has the atomic number 20.
• Its electronic configuration is 2,8,8,2.

Element C-

• Element C has the atomic number 10.
• Its electronic configuration will be 2,8.

Identification-

• Metals have 1,2, or 3 electrons in their valence shell.
• Non-metals have 4,5,6,7 electrons in their valence shell.
• Inert gases have a completely filled valence shell i.e., 2 electrons in Helium and 8 in other inert gases.
• Valence shell- The outermost orbital shell of an atom is called its valence shell.

Hence,

1. Element A is non-metal, as it has 7 electrons in its outermost shell.
2. Element B is metal, as it has 2 electrons in its outermost shell
3. Element C is chemically inert, as it has a completely filled outermost shell, having 8 electrons