Structure, Bonding and properties Why do atoms bond together?

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chemical bonding
0539 s18 qp 01

Ca
(2.8.8.2) + O (2.6)  Ca
2+
(2.8.8) O
2-
(2.8)
can be summarised electronically as [2,8,8,2] + [2,6]  ONE combines with ONE to form
Example 6:
A Group 3 metal + a Group 6 nonmetal eg aluminium + oxygen  aluminium oxide Al
2
O
3
or ionic formula (Al
3+
)
2
(O
2-
)
3
In terms of electron arrangement, 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. 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)  2Al
3+
(2.8) 3O
2-
(2.8)
can be summarised electronically as 2[2,8,3] + 3[2,6]  TWO combines with THREE to form
The Properties of Ionic Compounds

11 The alternate positive and negative ions in an ionic
solid are arranged in an orderly way in ab giant ionic lattice
structure shown on the left.

The ionic bond is the strong electrical attraction
between the positive and negative ions next to each other in the lattice.

The bonding extends throughout the crystal in all directions.

Salts and metal oxides are typical ionic compounds.

This strong bonding force makes the structure hard (if brittle) and have high melting and boiling points, so they are not very volatile!

The bigger the charges on the ions the stronger the bonding attraction eg magnesium oxide Mg
2+
O
2-
has a higher melting point than sodium chloride Na
+
Cl

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