1. The elements of life
EL1
What are we made of?

2. Elements and the body
As chemists we would probably say the body is made up of atoms, molecules, elements and compounds – a mixture of compounds
Elements in the body are classified as one of three types
Major constituent elements – make up 2-60% of all the atoms present in your body these are hydrogen, oxygen, carbon and nitrogen
Trace elements, which make up % e.g calcium and phosphorus
Ultra–trace elements which make up less than 0.01%, e.g. iron and iodine

3. Counting atoms of elements
mass in 60kg person / g
%age of atoms
oxygen
38 800
25.5
carbon
10 900
9.5
hydrogen
5 990 63
nitrogen
1 860
1.4
Mass and proportions of major constituent elements in a person of average mass (60 kg)

4. Counting atoms of elements
A list of masses alone doesn’t let us decide which elements are the most important to life.
We need to determine how many atoms of each element there are to do this we use moles
One mole is the number of atoms in 12 g of carbon 12 – 6.02 x 1023
There are over 1000 moles of carbon in the human body that’s a lot of carbon atoms
Table 1 shows us that the ratio of hydrogen to oxygen is approximately 2:1 – this is because 65% of your body is water – H2O