Question

The atomic number of sodium is 11. How many valence electrons does it have?

• A. 3
• B. 9
• C. 2
• D. 1

Answer 1

The correct option is D 1

The atomic number of sodium is 11, which means it has 11 electrons and 11 protons. We know that every shell has a different capacity of occupying electrons. The formula which gives the number of electrons that can accommodated in a shell = $2n^2$
1^st shell can have $2\times (1{)}^2=2$
2^nd shell can have $2\times (2{)}^2=8$
3^rd shell can have $2\times (3{)}^2=18$
As sodium has an atomic number of 11, the first and second shell will be filled and the third shell will have 1 electron. Valence electrons (VE) are the electrons in the outer shell of an atom. Hence sodium has 1 valence electron.