9701 MCQ Solution 14

Question 14: [Inorganic > Period 3]:

Which diagram represents the change in ionic radius of the elements across the third period (Na to Cl)?

Reference: Past Exam Paper – November 2002 Paper 1 Q14

Solution 14:

Answer: C.

Going across the third period the first 3 elements are metals. They will lose electrons from their valence shell to become ions. In this process they lose a shell and thus significantly decrease the size of their radius. The rest are non-metals and gain electrons to form ions. 

When they do this the valence shell becomes full. This is best depicted by the sudden rise in option C’s graph; the first line representing metal cations and the second line representing non-metal anions. 

Between the metal cations the nucleus of the ions increase in proton number, thus the effect of nuclear charge on the outer shell is greater, ultimately causing the radius to decrease. This is reason is the same for the non-metal anions. 

The decrease in radius between cations and anions is best shown by the negative gradient of the 2 lines in option C’s graph.