1. Atomic Structure Every substance is made up of atoms – e.g. water (H 2 0) is made up of two hydrogen atoms and one oxygen atom. However each of these atoms is made up of three smaller ‘sub-atomic’ particles – the electron, the proton and the neutron.

2. Sub-atomic Particles PositionMassCharge ElectronShells1/1836 ProtonNucleus1+1 NeutronNucleus10

3. Diagram of an Atom The shells contain the electrons. Shell 1 holds a maximum of 2 electrons Shell 2 holds a maximum of 8 electrons Shell 3 holds a maximum of 8 electrons The nucleus contains the protons and the neutrons. shells nucleus

4. Chemical Symbols Every element has a chemical symbol. e.g. hydrogen – H; lead - Pb On the periodic table each of these symbols has two numbers associated with it. E.g. Na The larger of the two numbers is the MASS NUMBER and represents the number of protons and neutrons in an atom. The smaller of the two numbers is the ATOMIC NUMBER and represents the number of protons (or electrons) in an atom. How many protons does sodium have? How many electrons does sodium have? How many neutrons does sodium have? 23 11

5. Protons, Neutrons and Electrons Use your copy of the periodic table to write out the atomic number and mass number and then work out the number of protons, electrons and neutrons in the following atoms: K; Ca; F; C; Ar; P. No. of protons = ATOMIC NUMBER No. of electrons = ATOMIC NUMBER No. of neutrons = MASS NUMBER – ATOMIC NUMBER

6. Electron Arrangements Na: atomic number = 11 mass number = 23 protons = 11 electrons = 11 neutrons = 12 electron arrangement = 2, 8, 1 The electrons are arranged in shells. e.g. Sodium contains 11 electrons – 2 in the 1 st shell, 8 in the 2 nd shell and 1 in the 3 rd shell. This can be represented in two ways: 1.Na – 2, 8,1 2.The diagram shown below: 23 11

7. Questions: For each of the following elements write out the information found in the red box on the previous page and then draw a diagram of the electron arrangement: O; Li; Al; Ne; Mg; Cl.