Sunday, 20 March 2016

1.32 explain, using dot and cross diagrams, the formation of ionic compounds by electron transfer, limited to combinations of elements rom groups 1, 2, 3 and 5, 6, 7

Dot and cross diagrams show what's happening regarding the electrons when ionic bonding happens, the best way to explain is just to show you

 Sodium Chloride (NaCl)
Sodium ions have the formula Na+ and chloride ions have the formula Cl-. To have an outer shell, sodium wants to lose an electron and chloride wants to gain an electron. To make this happen, sodium gives chloride an electron. In the exam, make sure the dots and crosses are clear.

Diagram of bonding in sodium chloride. A sodium ion (2,8)+ gives an electron to a chloride ion (2,8,8)-. Both ions have full highest energy levels.

Magnesium oxide (MgO)


Diagram of bonding in magnesium oxide. A magnesium ion (2,8)2+ gives two electrons to an oxide ion (2,8)2-. Both ions have full highest energy levels
Magnesium ions have the formula Mg2+, while oxide ions have the formula O2-. Magnesium gives oxygen two electrons
Calcium chloride, CaCl2 (a little trickier)
Diagram of bonding in calcium chloride. A calcium ion (2,8,8)2+ gives one electron to a chloride ion (2,8,8)- and another electron to another chloride ion (2,8,8)-. All three ions have full highest energy levels
Calcium ions have the formula Ca2+. Chloride ions have the formula Cl-. Calcium wants to lose 2 electrons but chloride only wants 1. Therefore, two chloride ions bond with one calcium ion, this means that each chloride ion gets 1 electron and calcium loses two, so everyone happy :)


Image source: bitesize
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