2g. The ionic bonding of the compounds sodium oxide Na₂O and potassium oxide K₂O

Example 2g. A Group 1 Alkali Metal combining with a Group 6 non–metallic element

* metals \ non-metals (zig-zag line)

e.g. sodium/potassium + oxygen ==> sodium/potassium oxide Na₂O/K₂O or ionic formula (Na⁺)₂O^2–/(K⁺)₂O^2–

In terms of electron arrangement in the formation of the ionic compound sodium oxide, the two sodium/potassium atoms donate their outer electron to one oxygen atom.

This results in two single positive potassium ions to one double negative oxide ion via electron transfer.

All the ions have the stable electronic structures 2.8.8 (argon like) or 2.8 (neon like).

Valencies, sodium/potassium 1, oxygen/sulfur 2. giving the following formulae:

Lithium oxide, Li₂O, sodium oxide Na₂O, sodium sulfide Na₂S and potassium K₂S etc.

2Na (2.8.1) + O (2.6) ==> 2Na⁺ (2.8.8) O^2– (2.8)

can be summarised electronically as 2[2,8,1] + [2,6] ==> [2,8]⁺₂ [2,8]^2–

so both the sodium and oxide ions have a full outer shell like a noble gas

TWO atoms combine withONE atom to form

or

+ + ==>

Note in this electron diagram, only the original outer electrons are shown above.

The outer electrons of the sodium atoms (2.8.1) are transferred to the outer shell of the oxygen atom (2.6) until it has a complete octet shell of outer electrons, just like a noble gas (2.8). At the same time, the sodium ion also attains a stable noble gas electron structure (2.8).

full electronic structure diagram of sodium oxide, the blue circle represents the nucleus.

The electronic dot & cross diagram for the ionic bonding in the ionic compound sodium oxide

is the Lewis diagram for the formation of sodium oxide

Melting point of sodium oxide is 1132^oC

2K (2.8.8.1) + O (2.6) ==> 2K⁺ (2.8.8) O^2– (2.8)

can be summarised electronically as 2[2,8,8,1] + [2,6] ==> [2,8,8]⁺₂ [2,8]^2–

so both the potassium and oxide ions have a full outer shell like a noble gas

TWO atoms combine withONE atom to form

Note in this electron diagram, only the original outer electrons are shown above.

The outer electrons of the potassium atoms (2.8.8.1) are transferred to the outer shell of the oxygen atom (2.6) until it has a complete octet shell of outer electrons, just like a noble gas (2.8). At the same time, the potassium ion also attains a stable noble gas electron structure (2.8.8).

full electronic structure diagram of potassium oxide,  the blue circle represents the nucleus.

The electronic dot & cross diagram for the ionic bonding in the ionic compound potassium oxide

is the Lewis diagram for the formation of potassium oxide

Solid sodium oxide and potassium oxide consist of a giant ionic lattice.

Melting point of potassium oxide is 740^oC

The electronic similarities between the two examples are very obvious.

Predicted formulae and names

All the formula highlighted in yellow can be described in the same way as sodium oxide, potassium oxide, sodium sulfide or potassium sulfide etc.

The Group 1 Alkali Metal atom loses one electron to form a singly charged positive ion

The Group 6 non–metal atom gains two electrons to form a doubly charged negative ion

Note that these formulae are empirical formula - the simplest whole number ratio of atoms in the formulae

The structures of these solid oxides and sulfides consists of a giant ionic lattice.

See also 2h. Details of ionic bonding in sodium sulfide & potassium sulfide (Group 1 + Group 6)