Interactive Chemistry Worksheets for Students |
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What is an atom?
An atom is the smallest particle of an element that has the properties of that element.
The Periodic Table lists the all the known elements. Each element is made up of its own type of atoms.
Atoms of elements vary in such properties as number of protons, Atomic weight and Atomic Radii or size
There have been various models that have been proposed to describe the structure of the atom.
- Billiard ball model - John Dalton
- Plum pudding model - J.J. Thomson
- Nuclear model - E. Rutherford
- Shell model of the atom - N. Bohr
- The quantum model of the atom - various scientists.
The atom consists of three subatomic particles. These particles are the proton, the neutron and the electron.
In a chemical reaction all the action takes place in the outer or valence shell of electrons.
What is a molecule?
A molecule is a group of atoms that joined together by one or more covalent bonds.
The above image represents a water molecule. The chemical formula for water is H2O. There are two hydrogen atoms that are joined to one oxygen atom.