1. Atomic Structure Atoms are not indivisible, but are made up of sub-atomic particles.

2. Sub atomic particles Atoms are made up of three types of particles; protons, neutrons and electrons. Protons Neutrons are found together in the nucleus. Electrons Orbit around the nucleus in shells.

3. Characteristics of particles. Protons are positively charged, with a mass of one. Neutrons are neutral, with no charge, and also have a mass of one. Electrons are negatively charged, but have a mass so small (around 1/2000 of a proton) that it is usually ignored.

4. ProtonNeutronElectron Mass 11 negligible Charge +1None

5. The atomic number (Z). The number of the protons in the nucleus is known as the atomic number. As atoms are neutral, they all have the same number of electrons as there are protons. So the atomic number also tells us the number of electrons in an atom.

6. Eg Oxygen Atomic number = 8 Number of protons = Number of electrons =

7. Mass number (aka nucleon number A) Number of protons NB Electrons do not count as their mass is so small. Number of neutrons The mass number = + The number of neutrons = Mass Number Atomic number -

8. Eg; Carbon Atomic Number = Mass number = The number of neutrons = Mass Number Atomic number - 12 6 12 – 6 = 6

9. How to find out the atomic number and mass number. Look at the periodic table. Each element is given two numbers. Na The upper number is the mass number. 23 The bottom number is the atomic number. 11

10. Use your periodic table to find out how many protons and electrons there are in; 1) Silicon 2) Uranium 3) Barium ion 4) A chloride ion 1) Atomic number = 14 so Si has both 14 protons and 14 electrons. 2) 92 of both 3) Atomic number = 56 so there are 56 protons, but two electrons are lost to form the ion = 54 4) Atomic number = 17, so there are 17 protons, but the ion has one more electron than the atom = 18.

11. Use the periodic table to find out the number of particles in; 1) Potassium atom 2) Oxygen molecule 3) Sulphide ion 4) Iron ion 1) Atomic number = 19, so 19 protons and electrons. Mass number = 39, so 39- 19 = 20 neutrons. 2) 2( 8p, 8e, 8n) = 16 each. 3) p 16, e16+2= 18, n 32- 16 = 16. 4) p 26, e 26-2 = 24, n 56- 26 =30.