Show the formation of MgCl2, Na2O …

Atomic number of Sodium (Na) – 11
Electronic configuration of Sodium – 1s² 2s² 2p⁶ 3s¹
It has one valence electron, it will lose one electron to get octet configuration
Atomic number of Oxygen (O) – 8
Electronic configuration of Oxygen – 1s² 2s² 2p⁴
It is two electrons short of octet configuration, thus it will gain two electrons.
During the bond formation between Sodium and Oxygen, two Sodium atoms loses one electron each to Oxygen atom.
2 Na -2e^-  →  2Na⁺
O + 2e^-     →  O^-2
 
2Na⁺ + O^-2 → Na₂O
 
Atomic number of Magnesium (Mg) – 12
Electronic configuration of Magnesium – 1s² 2s² 2p⁶ 3s²
It has two valence electrons, it will lose two electrons to get octet configuration
Atomic number of Oxygen (O) – 8
Electronic configuration of Oxygen – 1s² 2s² 2p⁴
It is two electrons short of octet configuration, thus it will gain two electrons.
During the bond formation between Magnesium and Oxygen, one Magnesium atom loses two electrons to Oxygen atom.
Mg -1e^-    →  Mg²⁺
O + 2e^-     →  O^-2
 
Mg⁺² + O^-2 → MgO