2i. The ionic bonding of the compound aluminium fluoride AlF₃

e.g. aluminium + fluorine ==> aluminium fluoride AlF₃ or ionic formula Al³⁺(F^–)₃ 

In terms of electron arrangement in the formation of the ionic compound aluminium fluoride, the aluminium donates its three outer electrons to three fluorine atoms forming a triple positive aluminium ion and three single negative fluoride ions.

The atoms have become stable ions, because aluminium and fluorine becomes electronically like neon via electron transfer.

Valency of Al is 3 and F is 1, i.e. equal to the charges on the ions.

Al (2.8.3) + 3F (2.7) ==> Al³⁺ (2.8) 3F^– (2.8)

can be summarised electronically as [2,8,3] + 3[2,7] ==> [2,8]³⁺ [2,8]^–₃

so both the aluminium and fluoride ions have a full outer shell like a noble gas

ONE atom combines withTHREE atoms

to form

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

The outer electrons of the aluminium atom (2.8.3) is transferred to the outer shell of the fluorine atoms (2.7) giving them a complete octet shell of outer electrons, just like a noble gas (2.8). At the same time, the aluminium ion also attains a stable noble gas electron structure (2.8).

full electronic structure diagram of aluminium fluoride, the blue circle represents the nucleus.

The electronic dot & cross diagram for the ionic bonding in the ionic compound aluminium fluoride

the Lewis diagram for the formation of aluminium fluoride

The structure of solid aluminium fluoride consists of a giant ionic lattice.

Melting point of aluminium fluoride is 1290^oC

Solid aluminium chloride/bromide/iodide have similar formula but are covalent when vapourised into Al₂X₆ dimer molecules, but AlCl₃ has an ionic lattice in the solid but solid AlBr₃ and AlI₃, are actually covalent molecules, but these points are best left for an advanced AS–A2 chemistry discussion, not for GCSE students!