ATOM
Atoms are very small, they are smaller than anything that we can imagine or compare with.
Relative Sizes
Radii (in m) Example
10–1 Watermelon
10–2 Ant
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 –
Element Symbol
Nitrogen N
Aluminium Al
Copper Cu
Fluorine F
Argon Ar
Barium Ba
Oxygen O
Gold Au
Potassium K
Silver Ag
Hydrogen H
Silicon Si
Bromine Br
Boron B
Iodine I
Sodium Na
Calcium Ca
Iron Fe
Sulphur S
Carbon C
Lead Pb
Magnesium Mg
Chlorine Cl
Zinc Zn
Uranium U
Cobalt Co
Neon Ne
Atomic masses of a few elements
Element Atomic Mass (u)
Hydrogen 1
Oxygen 16
Carbon 12
Nitrogen 14
Sodium 23
Magnesium 24
Sulphur 32
Chlorine 35.5
Calcium 40
MOLECULE
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
