Chemical formulae

Question 1

What is the formula of an element?

Answer 1

The formula of any element is its symbol. The exception to this are the diatomic elements. They exist as pairs of atoms joined together.

Question 2

What is a molecule?

Answer 2

A molecule is a group of two or more atoms, which are joined together by covalent bonds.

Question 3

What are the seven diatomic molecules?

Answer 3

Fluorine
Chlorine
Oxygen
Hydrogen
Nitrogen
Bromine
Iodine

Question 4

What is a compound?

Answer 4

A compound is made up of two or more elements chemically combined.

Question 5

How is the chemical formula of a two-element compound worked out?

Answer 5

The chemical formula is worked out by using the valency of the atoms involved in the bond.

Question 6

What is valency?

Answer 6

The valency is the number of electrons an atom can lose or gain to have a full shell of electrons, Elements in the same group have the same valency.

Question 7

what are the valencies for the groups 1-7

Answer 7

1-1
2-2
3-3
4-4
5-3
6-2
7-1

Question 8

What are the rules for writing chemical formula for a compound?

Answer 8

1. Identity and find the symbol(s) for the element(s) in the periodic table.
2. Write the valency at the top right-hand corner of each symbol
3. Use the cross over method( swap and drop)
4. write down the formula(simplest whole-number ratio of atoms)

Question 9

What happens if the valency of each element is the same?

Answer 9

If the valency of each element is the same then there is only one of each in the formula. The valencies cancel.

Question 10

What number do we not write in a formula?

Answer 10

Do not write the number ‘1’ in the formula.

Question 11

How do you find the group ions?

Answer 11

The group ions can be found on page 8 of the data booklet.

Question 12

Which group has its own valency?

Answer 12

Compounds with two or more elements ending in -ite and -ate contain groups of atoms. The group has its own valency which is equal to the size of the charge.

Question 13

What is the valency of the transition metals?

Answer 13

The valency of the transition metal is a roman numeral which is inserted into the name of the compound immediately after the name of the transition metal.

Question 14

What number is this roman numeral (I)?

Answer 14

One

Question 15

What number is this roman numeral (II)?

Answer 15

Two

Question 16

What number is this roman numeral (III)?

Answer 16

Three

Question 17

What number is this roman numeral (IV)?

Answer 17

Four

Question 18

What number is this roman numeral (V)?

Answer 18

Five

Question 19

What is this roman numeral (VI)?

Answer 19

Six

Question 20

What elements are the exception for the valencies of transition metals and have only one valency?

Answer 20

Zinc-2

Silver-1

Question 21

How do you write the formulae for a compound with a prefix?

Answer 21

If a compound has a prefix the valency rules do not apply.

Question 22

What number is the prefix mono?

Answer 22

One.

Question 23

What number is the prefix di?

Answer 23

Two.

Question 24

What number is the prefix tri?

Answer 24

Three

Question 25

What number is the prefix tetra?

Answer 25

Four.

Question 26

What is the prefix penta?

Answer 26

Five.

Question 27

What is the prefix hexa?

Answer 27

Six.

Question 28

What are ionic compounds made up from?

Answer 28

Ionic compounds are made up of ions. (Usually a metal ion and a non-metal ion). The ionic formula of a compound includes the charges of the ions.

Question 29

Do metals form positive or negative ions?

Answer 29

Metal form positive ions.

Question 30

Do non metals form positive or negative ions?

Answer 30

Non metals form negative ions.

Question 31

What is the valency of an ionic formulae?

Answer 31

The valency is the charge on the ion.

Question 32

Can the charge of an ion change?

Answer 32

The charge of an ion will never change.

Question 33

How do you workout the charge when writing ionic formula for an element?

Answer 33

For an element the charge is its valency then add + for metal ions and - for non metal ions.