Periodicity AS

Classification of elements in s, p, d blocks Elements are classified as s, p or d block, according to which orbitals the highest energy electrons are in. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Na Mg Al Si P S Cl Ar atomic radius (nm) 0 200 400 600 800 1000 1200 1400 1600 Na Mg Al Si P S Cl Ar 1st ionisation energy (kJ/mol) 0 500 1000 1500 2000 2500 3000 Na Mg Al Si P S Cl Ar Melting and boiling points (K) Atomic radius Atomic radii decrease as you move from left to right across a period, because the increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding. 1st ionisation energy There is a general trend across is to increase. This is due to increasing number of protons as the electrons are being added to the same shell There is a small drop between Mg + Al. Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the 3p subshell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy. There is a small drop between phosphorous and sulphur. Sulphur’s outer electron is being paired up with an another electron in the same 3p orbital. When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove. Melting and boiling points For Na, Mg, Al- Metallic bonding : strong bonding – gets stronger the more electrons there are in the outer shell that are released to the sea of electrons. A smaller positive centre also makes the bonding stronger. Higher energy is needed to break bonds. Si is Macromolecular: many strong covalent bonds between atoms, high energy needed to break covalent bonds– very high mp +bp Cl2 (g), S8 (s), P4 (S)- simple Molecular : weak van der waals between molecules, so little energy is needed to break them – low mp+ bp S8 has a higher mp than P4 because it has more electrons (S8 =128)(P4=60) so has stronger v der w between molecules Ar is monoatomic weak van der waals between atoms Exactly the same trend in period 2 Period 2 = Li, Be, B, C, N, O, F, Ne Period 3 = Na, Mg, Al, Si, P, S, Cl, Ar Exactly the same trend in period 2 with drops between Be & B and N to O for same reasons- make sure change 3s and 3p to 2s and 2p in explanation! Similar trend in period 2 Li,Be metallic bonding (high mp) B,C macromolecular (very high mp) N2 ,O2 molecular (gases! Low mp as small v der w) Ne monoatomic gas (very low mp)