1. Write the charges next to the different ions, use the examples given to help you
Positive ions
Charge
Negative ions
ammonium
NH4+ 1+
chloride
Cl− 1−
potassium K+
bromide
Br−
sodium
Na+
iodide I−
calcium
Ca2+ 2+
hydroxide
OH−
magnesium
Mg2+
nitrate
NO3−
copper(II)
Cu2+
oxide
O2− 2−
iron(III)
Fe3+ 3+
carbonate
CO32−
aluminium
Al3+
sulfate
SO42−

2. Answers

3. Ionic compounds Saturday, 24 November 2018
Key question:
How are the formulae of ionic compounds worked out?
Key words:
Ionic compounds
Formula
Compound ions
Starter: How is the periodic table useful when finding out the formula of different ions.
Specs:

4. Salt
An ionic compound composed of positive ions (cations) and negative ions (anions).

5. Working out a formula
Ionic compounds contain ions. You can work out the formula of an ionic compound if you know which atoms are in it. Ionic compounds are electrically neutral ( no charge) because they contain equal numbers of positive and negative charges. In NaCl one Na+ is needed for every Cl-.
So 1+ and 1- ion balance each other out.
The overall charge is 0.

6. Working out a formula
Many ionic compounds have ions with different numbers of charges. For example calcium chloride.
Give the group number for Ca and Cl:
Ca group 2, Cl is in group 7.
How many electron would Ca lose? 2
How many electron can 1 Cl gain? 1
How many Cl is needed for 1 Ca?
2, Ca wants to lose 2e-, hence 2 Cl will be needed
What are the charges on the ions?
Cl – and Ca2+
What is the overall charge on the ionic compound?
0 (2 Cl have -- and Ca has 2+, this will balance the charges out)

7. Working out a formula
At this point we know there are two chloride ions bonding with one calcium ions.
A formula has to contain symbols of participating ions and the number of these ions.
Metals should come first then non-metal.
CaCl
What about the numbers?
There is 1x Ca, but 2xCl. In chemistry we do not really write 1 (soooo lazy), but other numbers must be indicated by a subscript (small number on the bottom)
Ca1Cl2 → CaCl2.

8. Working out a formula
In an ionic compound ions have charges but the overall charge of the compound must be 0.

9. Compound Ions
Compound ions contain more than one element. For example the nitrate ion NO3- contain one nitrogen joined to 3 oxygen atoms and an extra electron. O N O O

10. Common Compound Ions You need to learn these!!!
Name
Symbol
Charge
Hydroxide
OH- 1-
Nitrate
NO3-
Carbonate
CO32- 2-
Sulphate
SO42-
Ammonium
NH4+ 1+

11. Writing these in a formula
If two or more compound ions of the same type are needed in a formula, the ion must be written inside brackets.
For example:
Magnesium Nitrate is Mg(NO3)2
This shows that the two positive charges on Mg2+ are balanced by the two negative charges from two NO3- ions.

12. To help use your starter question
Negative ions
chloride
iodide
oxide
Positive ions
potassium
calcium
iron(III)
aluminium
Negative ions
hydroxide
nitrate
carbonate
sulfate
Positive ions
sodium
magnesium
copper(II)
aluminium
ammonium

14. cation + anion -> Ionic Compound
What’s in the name?
cation + anion -> Ionic Compound
Ionic compounds ending in ‘-ide’- e.g Sodium Chloride
‘-ide’ ending compounds occur when two different elements combine.
Ionic compounds ending in ‘-ate’- e.g Copper sulphate
‘-ate’ ending compounds occur when three or more different elements combine and one of them is oxygen.
e.g. (Copper Sulphate= copper +sulphur + oxygen)
The ending gives a clue that the chemical is a compound. 4

15. Correctly name the following ionic compounds:
a NaI b CaCl2 c KOH e Al2O3 g Mg(NO3)2 h CaCO3 i Na2SO4
B-grade
a sodium iodide
b calcium chloride
c potassium hydroxide
e aluminium oxide
g magnesium nitrate
h calcium carbonate
i sodium sulfate