Atoms are very small, they are smaller than anything that we can imagine or compare with.
Radii (in m) Example
10–10 Atom of hydrogen
10–8 Molecule of haemoglobin
10–4 Grain of sand
10–9 Molecule of water
Dalton was the first scientist to use the symbols for elements in a very specific sense.
Berzilius suggested that the symbols of elements be made from one or two letters of the name of the element.
Symbols for some elements –
Atomic masses of a few elements
Element Atomic Mass (u)
A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that
substance. Atoms of the same element or of different elements can join together to form molecules.
Molecules of some compounds
Compound Combining Elements Ratio by Mass
Carbon dioxide Carbon, Oxygen 3:8
Water Hydrogen, Oxygen 1:8
Ammonia Nitrogen, Hydrogen 14:3