OCR Gateway Chemistry C4.2

Ionic bonding

HideShow resource information
  • Created by: abc
  • Created on: 05-05-13 12:10

Ionic bonding

Atoms with an outer shell of 8 electrons have a stable electronic structure. Atoms can be made stable by transferring electrons. This is called ionic bonding.

Metal atoms lose electrons to get a stable electronic structure. Therefore they form a positive ion, as there are fewer negatively charged electrons than positively charged protons.

Non-metal atoms gain electrons to get a stable electronic structure. If an atom gains electrons then a negative ion is formed.

During ionic bonding, the metal atom becomes a positive ion and the non-metal atom becomes a negative ion. These two ions then attract one another.

1 of 4

Ionic bonding

Dot and cross models are used to describe ionic bonding. Here is an example.

(http://scienceaid.co.uk/chemistry/fundamental/images/ionic.jpg)

2 of 4

Conducting electricity

The structure of sodium chloride or magnesium oxide is a giant ionic lattice, in which positive ions have strong electrostatic attraction to negative ions. Substances with this structure are always solids.

(http://cdn.transtutors.com/Assets/27082011-engineering181.gif)

Sodium chloride solution can conduct electricity.

Sodium chloride and magnesium oxide conduct electricity when they are molten, i.e. when when their ions can move freely.

3 of 4

Properties

The physical properties of sodium chloride and magnesium oxide mean that:

  • they have high melting points due to strong attractions between positive and negative ions
  • they don't conduct electricity when solid because the ions cannot move
  • they conduct electricity when in solution or as a molten liquid as the ions are free to move

The melting point of magnesium oxide is higher than that of sodium chloride because:

  • magnesium has a charge of 2+ and oxygen has a charge of 2-, as opposed to sodium (+) and chloride (-), so there are stronger electrostatic attractions between + and - ions
  • each magnesium atom donates two electrons to the oxygen atom, which makes a stronger bond than when sodium atoms transfer only one electron to chlorine atoms
  • magnesium ions have a very small radius, so magnesium can get much closer to oxygen and the bond is therefore stronger
4 of 4

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »