Unit 1 - Formulae

Question 1

What information does a chemical’s formula tell you?

Answer 1

It gives the number of atoms present in the molecule.

The formula of a covalent network or ionic compound gives the simplest ratio of atoms/ions in the substance.

Question 2

What do the following prefixes mean?

mono
di
tri
tetra

Answer 2

one atom
two atoms
three atoms
four atoms

Question 3

What is the formula for:

Sulphur Monoxide

Carbon Dichloride

Copper Tribromide

Phosphorus Tetrahydride

Answer 3

SO

CCl2

CuBr3

PH4

Question 4

What is meant by the valency of an atom?

Answer 4

Valency is the combining power of an element. Elements in the same group of the periodic table have the same valency. The valency of an element is related to how many electrons are in the outer shell.

Question 5

What is meant by the valency of an atom?

Answer 5

Valency is the combining power of an element. Elements in the same group of the periodic table have the same valency. The valency of an element is related to how many electrons are in the outer shell.

Question 6

What is meant by the valency of an atom?

Answer 6

Valency is the combining power of an element. Elements in the same group of the periodic table have the same valency. The valency of an element is related to how many electrons are in the outer shell.

Question 7

What are the valencies of elements in groups 1 to 8?

Answer 7

1
2
3
4
3
2
1
0

Question 8

If given the name of a compound, how can you work out the formula?

Answer 8

S.V.S.D.F system. (Valency cross over)

Step one - write down the symbols

Step two - write valency (USE DATA BOOKLET)

Step three - swap the valencies

Step four - if the valencies can be simplified, divide them both by the smaller of the two numbers. If one of the numbers is already one, then they cannot be divided and simplified any further.

Step five - write the formula.

Question 9

What is the formula of strontium chloride?

Answer 9

SrCl2

Question 10

What is the formula of Germanium sulfide?

Answer 10

GeS2

Question 11

How can you find out the valency of group ions?

Answer 11

In the data booklet (page 8)

We can take the number of charges on the ion as the valency of the ion.

(OH)- has a valency of 1

(SO4)2- has a valency of 2

Question 12

What is the formula of Magnesium Carbonate?

Answer 12

MgCO3

Question 13

Work out the formula of Beryllium Phosphate.

Answer 13

Be3(PO4)2

Question 14

Why do some compounds have roman numerals in their name?

Copper (II) chloride

Answer 14

Some elements do not always make the same number of bonds. These include some transition metals.

The valency of these elements is usually given in roman numerals inside brackets.

Question 15

What is the formula of:

Copper (II) chloride?
Copper (I) chloride?

Answer 15

CuCl2
CuCl

Question 16

What must be included when asked to write an ionic formula?

Answer 16

Charges on each ion.

One part will be positive and the other negative.

Question 17

What is the ionic formula for potassium nitrate?

Answer 17

Potassium makes 1 bond and will be positive. (Valency = 1)

Nitrate makes 1 bond and has a negative charge (from data booklet)

Formula = KNO3

Ionic formula = K+NO3-