1. Dot-and-cross diagram
Chemistry 5072
Dot-and-cross diagram

2. Ionic bonding
Hence the ionic bond is an electrostatic force

3. Ionic bonding
Ionic bonds are formed between atoms of metals and atoms of non-metals, as a result of the transfer of electrons.
Compounds formed by ionic bonding are called ionic compounds. Metals react with non-metals to form ionic compounds.
Note : The particles present in ionic compounds are ions; there are NO molecules in ionic compounds.

4. More Practice
1. Draw ‘dot and cross’ digrams to show the formation of :
Calcium oxide
Magnesium chloride
2. Draw ‘dot and cross’ diagram to show the bonding in
Sodium oxide

5. Calcium oxide (CaO) 2+ 2- x transfer of 1 electron x x x x x x x x x x
2,6
O atom
Ca atom
2,8,8,2 x x 2+ 2- x x x x x x x x x x x x x x x x x x
O2- ion
Ca2+ ion
Ionic bond
(electrostatic force)
2,8
2,8,8

6. Calcium oxide (CaO) Ca O 2+ 2- Ca O x transfer of 1 electron
Note: only
valence shells
are shown x
O atom
2,6
Ca atom
2,8,8,2 x x 2+ 2- x x x Ca x x O x x x
Ca2+ ion
Ionic bond
(electrostatic force)
O2- ion
2,8
2,8,8

7. 2 Magnesium chloride MgCl2 transfer of 1 electron x x x x x x x x
Cl atoms x x x
2,8,7 x
Mg atom
transfer of 1
electron
2,8,2 x x 2+ 2 x x x x x x x x x
Mg2+ ion
2,8
2,8,8
2 Cl¯ ions

8. 2 Cl Mg Cl Mg Cl Magnesium chloride MgCl2 transfer of 1 electron x
Cl atoms
2,8,7 x
Mg atom
transfer of 1
electron Cl
2,8,2 2+ x x 2
Note: only
valence shells
are shown x Mg x x Cl x x x x
Mg2+ ion
2,8
2,8,8
2 Cl¯ ions

9. Chemical formulae of ionic compounds
An easy method of writing a chemical formula involving 2 ions is to ‘criss-cross’ the charges
Eg. Write the formula of aluminium oxide.
Ions: Al3+ O2-
Chemical formula: Al2O3
Check that the total positive charge and total negative charge are equal

10. Chemical formulae of ionic compounds
Write the formula of magnesium carbonate.
Ions: Mg2+ CO3 2-
Chemical formula: MgCO3
Check that the total charges are balanced.
All subscripts are in the simplest set of whole numbers

11. Chemical formulae of ionic compounds
Write the formula of calcium nitrate.
Ions: Ca2+ NO3 -
Chemical formula: Ca(NO3)2
Check that the total charges are balanced.
subscript ‘1’ is not written
Polyatomic ions should be written within brackets if there is a subscript attached

12. Properties of ionic compounds
Physical properties:
High melting and boiling points
Usually soluble in water
Low volatility
Conducts electricity only in molten or aqueous state