JAMB Chemistry 1980 Question 18

Question 18

Atomic Structure

The following is an arrangement of elements in order of decreasing number of outer electrons; one of the elements is wrongly placed. Which is it? ALUMINIUM, CHLORINE, SILICON, MAGNESIUM AND SODIUM

A.Chlorine
B.Aluminium
C.Silicon
D.Magnesium
E.Sodium

Show the answer and explanation

Answer: B (Aluminium)

Explanation

Outer electrons: Cl 7, Si 4, Al 3, Mg 2, Na 1. Aluminium (3) is placed first but should come after silicon.