Ionic Bonding and Ions

Ionic bonding occurs when a metal gives away one or more electrons to a non-metal element in order to form a stable ionic compound where both ions have a full outer shell of electrons. For a good exam definition "ionic bonding is the electrostatic bond between oppositely charged ions"

Ionic bonding happens between non-metals and metals due to something called valency. Valency an indicator of how many bonds/links an element can make which is due to spare electrons in its outer shell. Group 1 and 2 metals like (magnesium and sodium) often bond ionically because they have 1 or 2 spare electrons in their outer shell which makes them unstable. On the other hand, non-metals in group 6 and 7 (like oxygen and chlorine) have 6 or 7 electrons in their outer shell meaning they are also unstable. In order to stabilize, the metals lose electrons whilst non-metals gain electrons; both of these lead to stable, charged ions. Because the ions are charged also, they attract to each other as opposite charges attract.
Compound (Adrien Olichon)

Lets try a worked example! The bonding of the ionic compound- Sodium Chloride.
  1. First we need to check the valency of each of our elements in order to know how many of each element we need. (Sodium and Chlorine both have a valency of 1 so one of each is needed)
  2. Once we know how many atoms of each are needed, we need to draw a diagram of the atom(s) for each.
  3. Because our sodium is in group 1, we know it has one spare electron in its outer shell that it needs to lose. Because our chlorine atom is in group 7, we know it has 7 electrons in its outer shell and needs to gain 1 to complete its outer shell. The spare sodium atom transfers onto the chlorine atom to create two stable but charged ions (see figure 1)
  4. The atoms become charge ions because they now have an imbalance of protons and electrons as they have more/less protons than before. When we draw ions (see figure 2) we draw a slightly enclosing box around the diagram and next to it the charge. If it has gained an electron (like our chlorine) then the sign will be a minus As there are more electrons than protons. If it loses an electron (like out sodium) then it will be positive as there are more protons than electrons.
  5. FIGURE 1 Dot and cross diagram (BBC GCSE bitesize)

FIGURE 2 Ionic compound (BBC GCSE bitesize)
Properties of ionic compounds include;
  • High melting points and boiling points
  • Hard and brittle crystals
  • Dissolves in water
  • As solid, does not conduct electricity because ions are not free to move
  • Conducts when molten or dissolved because ions are free to move
  • Strong electrostatic forces of attraction hard to break (therefore high MP and BP)
(Not for this topic but useful for chemistry) Note bond breaking is endothermic (requires energy) and bond making is exothermic (releases energy).

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