Elements A ([core]ns2) and B ([core]ns2np5) react to form ionic compound AxBy. Select the false statement below:

Question

Elements A ([core]ns²) and B ([core]ns²np⁵) react to form ionic compound A_xB_y. Select the false statement below:

1) x + y = 3

2) the first ionization energy of B is probably lower than the first ionization energy of A

3) the B in A_xB_y has a -1 oxidation state

the x and y in A_xB_y must reflect the lowest whole number ratio of moles of A to moles of B

4) element A serves as the reducing agent in the reaction to form A_xB_y

I am torn between number 2 and 4. If you will, please explain the reasoning behind your approach.

Answer 1

Given that #1 and #3 are true, i.e. A has oxidation state of 2+ and B of 1-, so form is AB₂ and x+y = 3, you are indeed left with choices #2 and #4 as being false. Since element A would have to lose/donate 2 electrons and each of element B would gain an electron, B would be reduced and A would be oxidized, making A the reducing agent. So, #4 would be true. As for #2, element B has 7 outer valence electrons and A has 2 (group 17 vs. group 2, but same period, i.e same n) so B is smaller and so first ionization energy is probably GREATER than that for A. My choice for the correct answer would be #2 as being a false statement.