Ionic Compounds

Note: Updated as of 2/1/13, and this blog is no longer being updated because I'm done with IGCSEs and am doing IB, which is seriously hectic. I apologise that this blog is not totally complete but it's all I have and I'm sorry. 

f) Ionic compounds

1.27 describe the formation of ions by the gain or loss of electrons

Ions are atoms or molecules with an electric charge due to the gain or loss of electrons. If electrons are lost, the ion has a positive charge. Metals tend to do this, so they form cations (positive ions), so normally elements from group 1-3 will form cations.

If electrons are gained, the ion has a negative charge. Non-metals tend to do this, and they form anions (A-Negative-ION - ANION). So elements from group 5-7 will form anions. Group 0/8 are the noble gases and are inert + unreactive, so they do not form ions.

1.28 understand oxidation as the loss of electrons and reduction as the gain of electrons

OILRIG -  Oxidation Is Lost, Reduction Is Gain

1.29 recall the charges of common ions in this specification

Positive ions/Cations			Negative ions/Anions
Charge	Name of ion	Formula	Charge	Name of ion	Formula
1+	Ammonium Copper (I) Hydrogen Lithium Potassium Silver Sodium	NH4+ Cu+ H+ Li+ K+ Ag+ Na+	1-	Bromide Chloride Hydroxide Fluoride Iodide Nitrate Hydrogencarbonate	Br- Cl- OH- F- I- NO3- HCO3-
2+	Barium Calcium Copper (II) Iron (II) Lead (II) Magnesium Nickel (II) Strontium Zinc	Ba2+ Ca2+ Cu2+ Fe2+ Pb2+ Mg2+ Ni2+ Sr2+ Zn2+	2-	Carbonate Sulphate Sulphite Sulphide Oxide	CO32- SO42- SO32- S2- O2-
3+	Aluminium Iron (III)	Al3+ Fe3+	3-	Nitride Phosphate	N3- PO43-

1.30 deduce the charge of an ion from the electronic configuration of the atom from which the ion is formed

So if the electronic configuration is 2.8.1, you can see that the atom has one outer shell electron only. And so it only needs to lost that to have a full outer shell. So its ion would have a positive 1 (1+) charge, as the electronic configuration would be 2.8. Basically, if there are less outer shell electrons to lose to have a full outer shell, then the charge will be positive. (Here, it is easier to lose than gain, because the ion would have to gain SEVEN electrons to have a full outer shell!)

Another example, if the electronic configuration is 2.8.7, then the atom only needs to gain 1 outer shell electron to have a full outer shell. So the ion formed would have the electronic configuration of 2.8.8, and so the charge would be negative 1 (you’re gaining one electron, which has a negative charge (1-) ). Thus if it is easier to gain electrons, (it is here, rather than losing 7 outer shell electrons), then the charge will be negative.

Here, the Sodium (Na) has lost one electron. It doesn't have equal numbers of protons and electrons anymore; it has one less electron than protons (or you can think of it as one more proton than electrons), so it has a 1+ charge. 

The chlorine, on the other hand, has gained one electron. So it has one more electron than proton, thus it has a negative 1 charge (1-). The formula for sodium chloride is NaCl. 

The magnesium atom loses 2 electrons to an oxygen atom, and they both have full outer shells now. It is common that ions form noble gas structures like this to become more stable and unreactive like the group 0/8 elements. 

The magnesium oxide is held together by very strong attractions between the ions. The ionic bonding is stronger here than in sodium chloride as this time you have 2+ ions attracting 2- ions. The greater the charge, the greater the attraction.

The formula for magnesium oxide is MgO.

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

This is a common example, it doesn't matter which element has dots/crosses for their electrons,  the important thing is to make it clear that the electrons are transferred from one atom to another to make 2 ions. The one losing an electron here is sodium, so it becomes a positive ion called a cation, and the chlorine atom gains an electron and becomes a chloride ion (an anion).


Magnesium oxide: MgO
Even though only one magnesium ion and one oxide ion is shown, the actual equation is:
2Mg + O₂ à 2MgO
(remember that oxygen is diatomic)

Calcium chloride: CaCl₂
However, here you have to show 2 chloride ions because calcium loses 2 electrons, and 2 chlorine atoms gain an electron each to form 2 chloride ions.

1.32 understand ionic bonding as a strong electrostatic attraction between oppositely charged ions

^self-explanatory

1.33 understand that ionic compounds have high melting and boiling points because of strong electrostatic forces between oppositely charged ions

The strong electrostatic forces between oppositely charged ions are ionic bonds as mentioned in the previous spec point. And these require a lot of energy to break, hence high melting/boiling points.