IMAT 2012 Q64 [Ions]

What is the total number of electrons in the ions of sodium chloride?

A. sodium ion = 11; chloride ion = 17
B. sodium ion = 8; chloride ion = 8
C. sodium ion = 11; chloride ion = 18
D. sodium ion = 10; chloride ion = 18
E. sodium ion = 10; chloride ion = 17

Sodium Chloride is an ionic compounds with ionic bonds; meaning one element loses a number of electrons and another gains them.

You should know these atomic numbers and that electron and proton/atomic number is the same in a neutral atom: Na_{11} and Cl_{17}

This is a redox reaction: Na^0 + Cl^0 \rightarrow Na^1Cl^1

Where Sodium loses an electron (oxidises): Na^0 -e\rightarrow Na^1
And so goes from 11 electrons to 10.

The answer is either D or E.

Chlorine reduces: Cl^0 + e \rightarrow Cl^{-1}
And so gains an electron, and goes from 17 to 18 electrons.

The answer is D.