2i. The ionic bonding of the compound aluminium fluoride
Doc Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A level US grade 9-12 level Revision Notes
Example 2i. A Group 3 metal combining with a Group 7 halogen non–metal
* metals \ non-metals (zig-zag line)
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.
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
Melting point of aluminium fluoride is 1290oC
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!
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