Question

Oxygen has a smaller radius than Selenium because the valence e- of oxygen experience much less e-/e- repulsion True or false

Answer 1

Ans : False

Both oxygen and selenium have six valence electrons but in differents shells. The valence electrons of oxygen are in 2nd shell and that of selenium in 4rth shell.

So the same number of electrons are contained in different sized shells of these atoms. The fourth shell of Se is larger than the 2nd shell of Oxygen so it faces less e-/e- repulsion and oxygen faces more e-/e- repulsion.

The smaller radius of oxygen is due to the fact that the electrons face more net effective charge from the nucleus than the selenium.