(i) The sodium atom `(Na)` has 1 outermost electron (or 1 valence electron) so its electron-dot structure is `Na`, the oxygen atoms `(O)` has 6 outermost electrons (or 6 valence electrons) , so its dot structure is `:overset(..)(O):`
and the magnesium atom `(Mg)` has 2 outermost electrons (or 2 valence electrons) so its electron -dot structure is `Mg`:
(ii) (a) Formation of `Na_(2)O`
`Na_(2)O` is sodium oxide. In the formation of sodium oxide thwo sodium atoms tansfer their 2 outermost electrons to an oxygen atom. By losing 2 electrons the two sodium atoms form two sodium ions `(2Na^(+))` . And by gainng 2 electrons, the oxygen atom forms an oxide ion `(O^(2-))`
The oppositely charged sodium ions and oxide ioon are together by strong electrostatic forces of attraction to form the ionic sodium oxide compound `2Na^(+)O^(2-)` or `Na_(2)O`.
(b) Formation of `MgO`
`MgO` is magnesium oxide. In the formationof agnesium oxide, a magnesium atom transfers its 2 outermost electrons to an oxygen atom. By losing 2 electrons a magnetsium atom forms mangesium ion `(Mg^(2+))` and by gaining 2 electrons the oxygen atom forms and oxide ion `(O^(2-))`:
The oppositely charged mgnesium ions and oxide ions are held together by stong electrostatic forces of attraction to form the ionic magnesium oxide compound `Mg^(2+) O^(2-)` or `MgO`
(iii) (a) The ions present in sodium oxide `(Na_(2)O)` compound are sodium ions `(Na^(+))` and oxide ions `(O^(2-))`
(b) The ions present in magnesium oxide `(MgO)` compound are magnesium ions `(Mg^(2+))` and oxide ions `(O^(2-))`
