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2j. The ionic bonding of the compound aluminium oxide

Doc Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A level US grade 9-12 level Revision Notes

Example 2j. A Group 3 metal combining with a Group 6 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

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

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 OXIDE: where the elements aluminium and oxygen are in the Periodic Table


e.g. aluminium + oxygen ==> aluminium oxide Al2O3 or ionic formula (Al3+)2(O2–)3

In terms of electron arrangement in the formation of the ionic compound aluminium oxide, two aluminium atoms donate their three outer electrons to three oxygen atoms.

This results in two triple positive aluminium ions to three double negative oxide ions via electron transfer.

All the ions have the stable electronic structure of neon 2.8. Valencies, Al = 3 and O = 2

2Al (2.8.3) + 3O (2.6) ==> 2Al3+ (2.8) 3O2– (2.8)

can be summarised electronically as 2[2,8,3] + 3[2,6] ==> [2,8]3+2 [2,8]2–3

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

TWO  (c) doc batoms combine withTHREE (c) doc b atoms to form (c) doc b(c) doc b

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

The three outer electrons of the aluminium atoms (2.8.3) 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 aluminium ion also attains a stable noble gas electron structure (2.8).


The charge on the aluminium ion Al3+ is +3 units (shown as 3+) because there are three more positive protons than there are negative electrons in the aluminium ion.

The charge on the oxide ion O2– is –2 units (shown as 2–) because there are two more negative electrons than there are positive protons in the oxide ion.

full electronic structure of aluminium oxide

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

Lewis diagram for the formation of the ionic compound aluminium oxide

Melting point of aluminium oxide is 2072oC


What next?

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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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