Atoms X and Y form an ionic compound with formula XY_2.

Which option below could give the correct atomic numbers for X and Y?

A. X = 11; Y = 16

B. X = 3; Y = 17

C. X = 12; Y = 9

D. X = 6; Y = 16

E. X = 14; Y = 8

Atoms X and Y form an ionic compound with formula XY_2.

Which option below could give the correct atomic numbers for X and Y?

A. X = 11; Y = 16

B. X = 3; Y = 17

C. X = 12; Y = 9

D. X = 6; Y = 16

E. X = 14; Y = 8

When looking at XY_2, we can conclude that for this compound to form, X must have double the valency of Y. This is why it would take two atoms of Y to react with one atom of X.

Let’s look at the electron configuration of each option:

For A,

X= 2,8,1 and Y= 2,8,6

This would take two atoms of X to react with one atom of Y, which is incorrect.

For B,

X= 2,1 and Y= 2,8,7

This would take one atom of X to react with one atom of Y, which is incorrect.

For C,

X= 2,8,2 and Y= 2,7

This would take two atoms of Y reacting with one atom of X, which is correct and our answer.

For D,

X= 2,4 and Y= 2,8,6

These atoms will share electrons, which is incorrect.

For E,

X= 2,8,4 and Y=2,6

These atoms will share electrons, which is incorrect.