Elements

Elements = Consist of atoms with the same atomic number

The number of protons in a nucleus decides what type of atom it is. E.g. 1 proton = Hydrogen, 2 protons = Helium

If a substance only contains atoms with the same nuber of protons it is an element.

Atoms can be represented by a one or two letter symbol. This means you do not have to write the full name of the atom. E.g. Carbon = C, Magnesium = Mg

Most of these symbols come from the latin names of the elements

Isotopes are different forms of the same element which have the same number of protons but different number of neutrons. They have the same atomic number but different mass numbers.

For example:

Carbon 12              Carbon 13

6 protons                6 protons

6 electrons             6 electrons

6 Neutrons             7 neutrons

Because many elements can exist as a number of different isotopes, relative atomic mass is used instead of mass number when referring to the elemnt as a whole. This is an average mass taking into account the different masses and abundances of all the isotopes that make up the element.

Relative atomic mass = sum of (isotope abundance x isotope mass number) ÷ sum of abundance of all the isotopes