ATOMS

To start of with you need to get your head round all the basics. I have a list of all the spec points that you need for the exam and I will try and go through them as easily as possible, but lets start at the beginning first.

Everything is made up of atoms, you know that, right? But the real question is what are made up of, for it definitely cannot be something "indivisible" as its name suggests. Well, it's not.

An atoms is made up of essentially two "parts", if you don't mind me putting it that way. The centre of the atoms is the NUCLEUS of positive charge, this is because it is made up of protons with +1 charge and neutrons, which are neutral. Now the atom itself is neutral so you need something to cancel out the charge. Dead easy, electrons -1 negative charge, which exist in shells around the nucleus.

A proton and neutron both have a relative mass of 1, whilst the mass of an electron is very small: 1/2000 of a proton. That's relative mass, for those more interested in actual numbers, the mass of an electron is actually 9.11 × 10-31 kg.

The number of protons (atomic number) in a nucleus is equal to the number of electrons in that atom - the charges have to cancel out.

The term ISOTOPE means an atom of an element with different number of neutrons and different mass.

It is also important to note that all relative masses are compared to the C12. Hence the definition of relative atomic mass is the weighted mean mass of an atom compared to one 12th of carbon 12 atom.

When given the abundance of the isotopes of an element, the relative atomic mass is easy to calculate. First multiply the mass by the abundance. Add up the different values. And divide by 100.