1.4 Chemical Formulae

Question 1

What is valency?

Answer 1

Valency is combining power. It is indicated by:
* Prefix (di… tri… tetra… etc.)
* group
* roman numeral (iron (III))

Question 2

What are the suffixes and what do they mean?

Answer 2

• -ide: only 2 things in the compound/molecule (sodium chloride - NaCl)
• -ite/ate: contains 3 things including oxygen (calcium carbonate - CaCO3)

Question 3

How do you work out a formula?

Answer 3

• Symbol - C S
• Valency - 4 2
• Swap - 2 4
• Simplify - 1 2
• Formula - CS2 (Carbon Sulphide)
  For ions containing more than one atom, their formula & valency is shown in the data book.

Question 4

What is GFM?

Answer 4

GFM (gram formula mass) is the mass of one mole of the molecule.

Question 5

How do you work out the GFM of Na2CO3?

Answer 5

Na=2x23=46
C=1x12=12
O=3x16=48
46+12+48=106g

Question 6

What are the state symbols?

Answer 6

Solid - s
Liquid - l
Gas - g
Aqueous - aq

Question 7

What is an ionic formula?

Answer 7

A chemical formula showing the charges on each ion

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The positive and negative charges shown in an ionic formula should always balance

Question 8

What is a group ion?

Answer 8

An ion containing more than one type of atom