An Atom consists of 3 sub-atomic particles
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An atom can be divided into 2 parts. 1. The Nucleus: 
2. The Electrons Shells: 
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Atoms are really minute things. They are far too small to see, even with a most powerful microscope.
An atom is a neutral particle, because it has no overall charge. The positively charged protons are equal in number to negatively charged electrons, therefore they cancel each other out. Hence, in an atom number of PROTONS always equals number of ELECTRONS. The charge on an electron is the same size as the charge on the proton, but opposite.
If an atom gains or loses electrons, then it becomes charged. In this state it is called an ION.
The number of neutrons in an atom are not a fixed number. They are usually just a little higher than the proton number.
Summary
| Mass | Charge | Comment | |
| Proton | 1 | +1 | Heavy and positively charged |
| Neutron | 1 | 0 | Heavy but neutral |
| Electron | 1/2000 | -1 | Minute and negatively charged |
Atomic Number and Atomic Mass
If you look at the PERIODIC TABLE, for each element you will see two numbers. The smaller of the two numbers is called the ATOMIC NUMBER and bigger one is called the ATOMIC MASS.
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Remember:
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3. To find out the number of neutrons in an atom, just take away the atomic number from the atomic mass. 4. The atomic number is the smallest of the two numbers. the bigger number tells you the relative atomic mass of an atom. 5. The mass number is always nearly double the atomic number. |
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