Small Particles of Matter

So the Nucleus contains 2 different types of particles, the Proton and the Neutron, outside the Nucleus lie the electrons. To describe electrons as lying there is wrong, in fact the electrons go whizzing around the atoms but they do so in specific orbits often called shells.

elektron, the Greek word for "amber"

define atomic number and isotope

atomic number

Each element is made up of different types of atoms,

the atoms in these elements differ because the number of protons for each element is different.

The Atomic number is equal to the number of protons in an atom.

The number of electrons is usually the same as the number of protons, as there is no net charge on an atom, they are neutral. The number of neutrons varies from element to element obviously but also differs from atom to atom, the ne

Mass number

There is another number that is always listed with the symbol for the element, this is the mass number.

The mass number is defined as the number of protons + the number of neutrons together.

To find the number of Neutrons

# neutrons = Mass Number - Atomic Number

The Mass number will be the bigger number in the atomic symbol (except for hydrogen which usually does not have a neutron attached).

Mass number

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/chemcalc/chemcalc_bothrev1.shtml

Isotopes

An Isotope of an element are two atoms that have the same number of protons

but have different numbers of neutrons.

Where the decimal comes from in the Mass No.

The mass numbers of elements often has a decimal in it. There can be no such thing as a fraction of a proton, this decimal is found by finding the average of all the isotopes found in nature.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/chemcalc/chemcalc_bothrev2.shtml

More on Molecules here

Bohr Diagrams

Electrons

How small are atoms

Test your knowledge of the atomic structure here

http://www.sciencequiz.net/jcscience/jcchemistry/atomstruct/atomicstmc1a.htm