Atoms, Elements & Compounds

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Atoms

All atoms consist of a nucleus and a cloud of electron that move around the nucleus. The nucleus is made up of protons and neutrons.

Subatomic Particle Mass Charge Where

Proton 1 +1 nucleus

Electrons 1/2000 -1 shell

Neutron 1 0 nucleus

0.00013 micron - The size of an atom

Mass Number

Bigger than atom's number

Changes by irregular amounts

No. of Protons + No. of Neutrons

Atomic Number

Number of protons in an atom

Every atom has an equal number of protons and electrons. Because of thin atoms have no overall change.

Mass number or nucleon number - The number of protons and neutrons in an atom

Electronic Configuration

Rules of filling shells

1st Shell - 2e-

2nd Shell - 8e-

3rd Shell - 8e-

Isotopes

The number of neutrons in an atom can vary slightly. For example, there are three kinds of carbon atom, called carbon - 12, carbon -13 and carbon - 14. They all have the same number of protons (because all carbon atoms have 6 protons - its atomic number), but the number of neutrons varies. These different atoms of carbon are called isotopes.

Isotopes are atoms that have the same atomic number, but different mass numbers. They have the same number of protons, but different number of neutrons.

The fact that they have varying number of neutrons, make no difference whatsoever to their chemical reactions. The chemical properties are governed by the number and arrangement of the electrons and, as you will see shortly, that is identical for all three isotopes.

Ions

Charge atom ie - different no. of e- Eg (1+ has lost e-)

The electrons

Atoms are electrically neutral, and the positiveness of the protons is balanced by the negativeness of the electrons. In a neutral atom. It follows that:

Number of electrons+ Number of protons

So, if an oxygen atom (atomic number = 8) has 8 protons, it must also have 8 electrons; if a chlorine atom (atomic atom = 17) has protons, it must also have 17 electrons.

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