Chemical formulae

Question 1

What is a chemical formula?

Answer 1

The chemical formula of a covalent molecular substance gives the number of atoms per molecule. The formula of a covalent network or ionic compound gives the simplest ratio of atoms/ions in the substance.

Sometimes the name of the compound gives information about the formula of that compound. Names of these compounds have prefixes that give the number of atoms of certain elements in each molecule.

Question 2

What number does each prefix correspond with

Answer 2

Mono- 1
Di- 2
Tri- 3
Tetra- 4
Penta- 5
Hexa- 6

Question 3

How many numbers of elements does the endings of compounds correspond with

Answer 3

ide- Two
ite- Three (one being oxygen)
ate- Three (one being oxygen)

Question 4

What is a valency

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 valency equals what group number

Answer 5

G, V
1,1 +
2,2 +
3,3 +
4,4
5,3 -
6,2 -
7,1-
8,0

Question 6

Roman numerals in elements

Answer 6

Some elements, particularly the transition metals, do not always have the same valency in their different compounds. The valency of these elements is usually given in roman numerals inside brackets.

• copper (I)oxide
  = Cu2O