Question

Look at the relative position of each pair of atoms listed here in the periodic table. How many core electrons does each have? How many valence electrons does each have?

1. Carbon and Silicon
2. Oxygen and sulphur
3. Nitrogen and Phosphorous
4. Magnesium and Calcium

Short answer

Pair of atoms	Number of Core electrons	Number of Valence electrons
a.Carbon Silicon	2 10	4 4
b. Oxygen Sulphur	2 10	6 6
c. Nitrogen Phosphorous	2 10	5 5
d. Magnesium Calcium	10 18	2 2

Step-by-step solution

Definition of core electrons and valence electrons

Core electrons are the ones not participating in bond formation. They are found in the inner orbital of an atom.

Valence electrons are found in the outermost orbital of an atom.They actively participate in bond formation.

Subpart (a) Finding the number of core and valence electrons of carbon and silicon.

Carbon

Electronic configuration- 1s² 2s² 2p²

No. of core electrons- 2

No. of valence electrons- 4

Silicon

Electronic configuration- 1s² 2s² 2p⁶ 3s² 3p²

No. of core electrons- 10

No. of valence electrons-4

Subpart (b) Finding the number of core and valence electrons of oxygen and sulphur

Oxygen

Electronic configuration- 1s²2s²2p⁴

No. of core electrons- 2

No. of valence electrons- 6

Sulphur

Electronic configuration- 1s²2s²2p⁶3s²3p⁴

No. of core electrons- 10

No. of valence electrons- 6

Subpart (c) Finding the number of core and valence electrons of nitrogen and phosphorus.

Nitrogen

Electronic configuration- 1s²2s²2p³

No. of core electrons- 2

No. of valence electrons- 5

Phosphorous

Electronic configuration- 1s² 2s² 2p⁶3s²3p³

No. of core electrons- 10

No. of valence electrons- 5

Subpart (d) Finding the number of core and valence electrons of magnesium and calcium.

Magnesium

Electronic configuration- 1s²2s²2p⁶3s²

No. of core electrons- 10

No. of valence electrons- 2

Calcium

Electronic configuration- 1s²2s² 2p⁶3s²3p⁶4s²

No. of core electrons- 18

No. of valence electrons- 2