Monday_16: Lesson 12 Ionic compounds

• Chemistry
• Secondary Education

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CHEMISTRY 10

12 - Formulae of Ionic Compounds

• I can deduce the formula of an ionic compound from the relative numbers of the ions present in a model or a diagrammatic representation or from the charges on the ions.

Use the compounds’ properties to decide whether they are ionic or covalent.

ionic

covalent

covalent

covalent

ionic

covalent

ethanol

carbon tetrachloride

glucose

table salt

water

potassium permanganate

How many atoms of different elements are there in the formulae of the following compounds?

How many atoms of different elements are there in the formulae of the following compounds?

Nitric acid, HNO3

How many atoms of different elements are there in the formulae of the following compounds?

Copper nitrate, Cu(NO3)2

How many atoms of different elements are there in the formulae of the following compounds?

Ammonium sulfate, (NH4)2SO4

How many atoms of different elements are there in the formulae of the following compounds?

Potassium manganate (VII), KMnO4

The dot-and-cross diagram helps keep track of electron transfers in bonding and ensures that the octet rule is obeyed.

The dot-and-cross diagram helps keep track of electron transfers in bonding and ensures that the octet rule is obeyed.

ratio of the ions in a compound

Chemists use a special kind of shorthand called a chemical formula to communicate this ratio. 

A chemical formula provides the:

• elements that make up the compound and
• number of atoms of each element that is present in a compound.

• Complete the figure below by adding the valencies (combining power) of the atoms shown.
• Which atoms in the figure below lose electrons when they form ions?
• Which atoms in the figure below gain electrons when they form ions?
• Name two atoms in the figure below that share electrons when they form compounds.

Valency (Combining Power)

Writing the chemical formulae of ionic compounds

1.  Write the unbalanced formula. Remember that the metal is first and the non-metal is second.
2.  Place the valence of each element on top of the appropriate symbol.
3.  Using arrows, bring the numbers (without the signs) down to the subscript positions by crossing over.
4.  Check the subscripts. Any subscript of “1” can be removed.

Valency (Combining Power)

Write the chemical formulae of the following.

Write a balanced formula for a compound that contains sulfur and each of the following elements. Use a valence of −2 for sulfur.

• (a) sodium 
• (b) calcium 
• (c) barium
• (d) aluminium 
• (e) rubidium 
• (f) hydrogen

Write the chemical formulae of the following.

Write a balanced formula for a compound that contains calcium and each of the following elements.

• (a) oxygen 
• (b) sulfur 
• (c) chlorine
• (d) bromine
• (e) phosphorus
• (f)  fluorine

Valency (Combining Power)

Writing the chemical formulae of ionic compounds

1.  Write the unbalanced formula. Place brackets around any polyatomic ions that are present.
2.  Write the valence of each ion above it. 
3.  Cross over, and write the subscripts.
4.  Tidy up the formula. Remember that you omit the subscript if only one particle exists in the ionic compound or molecule. Here, the brackets are no longer needed so that they can be removed.

lithium +

• nitrate
• hydroxide
• carbonate
• sulfate
• phosphate

magnesium +

• nitrate
• hydroxide
• carbonate
• sulfate
• phosphate

Write the chemical formulae of the following.

Write a chemical formula for a compound that contains sodium and each of the following polyatomic ions:

(a) nitrate 

(b) sulfate 

(c) hydroxide

(d) phosphate 

(e) carbonate

A. Write the valences for the elements in each compound. If the compound is ionic, indicate the charge associated with each valence.

• (1) AgCl 
• (2) TiO2 
• (3) CaO
• (4) Mn3P2 
• (5) FeS

B. Write the chemical formula of each compound.

• (6) tin (II) fluoride
• (7) barium sulfate
• (8) hydrogen chloride
• (9) caesium bromide
• (10) ammonium nitrate