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Thursday, February 11, 2010

What are atoms?

Atoms are the basic constituent of matter. Hence matter is made of atoms arranged in a particular way . Of course there are different types of atoms and the type of atoms and the type of arrangement will determine the type of matter.

We are now going to see a simple model of the atom and what are the different constituents of the atom.


The atom is composed of three basic constituents.

  1. The proton
  2. The neutron
  3. The electron

All the different types of atoms will have these three constituent particles. However the number of each will differ from one type of atom to another. We can thus deduce that it is the combination of these three constituent particles that determine the nature of the atom.

However in neutral atoms the number of proton is the same as the number of electron. If the two differs it means that the atom is charged. If there are more protons that electrons then the atom is positively charged and if the number of electron is greater than the number of proton then it means that the atom is negatively charged.


The table below lists the properties of the different constituent particles of the atom.






Mass 1.67 x 10–27 kg 1.67 x 10–27 kg 9.10 x 10-31 kg
  The proton and the neutron is on average 10000 times more massive that the electron    
charge +1.60 x1019 C No charge
This is because as you will see later on in radioactivity it is composed of one proton and an electron. The two opposite charges thus cancel each other
-1.60 x10-19 C
Location In the nucleus In the nucleus In orbits around the nucleus

As we have seen in the table above the neutron and the proton are present in the nucleus while the electron is present in orbits around the nucleus (They are in reality different  but we assume that they are planet-like in this model).

A model of the atom is shown below in fig 1


Fig 1

This model is a mere representation of the atom. You will learn later on how the electrons would be arranged if there are more than four. The size of the nucleus is also quite small. So small that its diameter is 10000 times smaller than the radius of the atom. Thus to represent it truly on fig 1 a tiny dot would have been more appropriate.

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