An Atom consists of 3 sub-atomic particles






An atom can be divided into 2 parts.

1. The Nucleus:

Atom 13
  • It is the centre of the atom.

  • And from the size point of view, it is very small compared to rest of the atom.

  • It contains protons and neutrons.

  • Protons are positively (+VE) charged sub-atomic particles.

  • Neutrons have no charge.

  • Nearly all the mass of the atom is made up of these two sub-atomic.

2. The Electrons Shells:

Atom 12
  • These are located around the nucleus.

  • Electrons are found in them

  • These electrons follow the path of the shell around the nucleus.

  • Electrons are negatively (-VE) charged sub-atomic particles and are very tiny, yet they cover a lot of space in an atom.

  • Their mass is negligible (virtually no mass).

  • The outer shell  electron(s) are involved in chemical reactions.

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.



  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.

  • The atomic number tells you how many protons there are in the nucleus of an atom.

  • This also tells you the sum of electrons in an atom.
  • 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.



     They have the same atomic number, but different atomic mass

    Isotopes are atoms of an element with the same number of  protons but different number of neutrons.

    An example of an isotope - Carbon

    Carbon - 12

    Carbon 12

    6 Protons

    6 Electrons

    6 Neutrons

    Carbon - 14

    Carbon 14

    6 Protons

    6 Electrons

    8 Neutrons

    The chemistry of an element is dependent on the number of electrons in its atomIf the atomic number is the same, then they must have the same number of protons.  This means they also have same number of electrons.  Therefore, the chemistry of the isotopes must be the same.  The different number of neutrons in the nucleus have no effect on its chemical behavior.



    Tags:Atoms, Protons, Electrons, Neutrons, Isotopes, Atomic bonding, how do atoms bond, ionic bonds form between molecules that have, chemical bonds ionic bonds, how are ionic bonds form, electron bond, ionic bond, covalent bond



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