Question

Which monatomic ions would you expect radium (z = 88) and selenium (z = 34) to form?

Answer 1

Radium belongs to 2nd group (Magnesium family) which means it will give +2 ion.
Ra2+

Selenium belongs to Oxygen family which means it will give -2 ion.
Se2-

Answer 2

1) Radium will form Ra²⁺ ions, because it is metal with two valence electrons (7s²) and it will lost two electrons to have electric configuration like noble gas radon (Z=86).

Electroic configuration of radium atom:

₈₈Ra 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰4f¹⁴5s²5p⁶5d¹⁰6s²6p⁶7s².

2) Selenium wil form Se²⁻ ions, because it is nonmetal and it has six valence electrons (4s²4p⁴), it will gain two electrons to have electron configuration like noble gas krypton (Z=36).

Electronic configuration of selenium atom: ₃₄Se 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁴.