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)

Pd metals Part of the modern Periodic Table

Pd = period, Gp = group

metals => non–metals
Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0
1

1H  Note that H does not readily fit into any group

2He
2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn
Ionic compound ALUMINIUM FLUORIDE: where the elements aluminium and chlorine are in the Periodic Table

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 (c) doc batom combines withTHREE (c) doc batoms to form (c) doc b(c) doc b

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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Sub-index for: Part 2 Ionic Bonding: compounds and properties

 

Index for ALL chemical bonding and structure notes

 

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