An analysis of 1st Ionisation Energy graph trends for the Group 2 [Alkali Earth] the Period 3 elements
...2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 (axn) The table clearly showhow th attraction between nucleus and electron is inversely proportional to the atomic numbe However, the graph shows that the rate of decrease changes at Calcium – from Beryllium to Calcium the decrease in ionisation energy is (899.4 – 589.7)/16 = 19.36 kJ mol-1 (2dp) as the atomic number increases by one; from Calcium to Barium the decrease is (589.7 – 502.8)/36 = just 2.41 kJ mol-1 (2dp). Looking back at the electron configuration table, this smaller rate of decrease can be explained… There are two extra energy levels in Calcium than Magnesium, and also two extra energy levels between Strontium and Calcium. However, the introduction of level ‘d’ in Strontium means that instead of one extra ‘p’ and one extra ‘s’ level (two more energy levels carrying a further 8 electrons), there is one extra ‘d’ and one extra ‘p’ level (two more energy levels carrying a further 16 electrons). So even though the increase in distance remains the same (as two energy levels are added each time), there are 16 more protons as opposed to 8, increasing the force of attraction and therefore more greatly compensating for the increase in distance, so the decrease in ionisation energy level is less significant. . . THE PERIOD 3 ELEMENTS The trend is very different to that of Group 2, as both increases and decreases are present, though generally there is an increase in ionisation energy level across the period. In the group 2 graph all atoms had the same number of electrons in the outer energy, something which atoms do not have in common in period 3. This fact makes a significant impact on ionisation energy level… As previously mentioned, net attraction has an impact on ionisation energy level. Here is a table to show net attraction for the period 3 elements: Symbol Protons Shielding Electrons Net Attraction Na 11 10 +1 Mg 12 10 +2 Al 13 12 +1 Si 14 12 +2 P 15 12 +3 S 16 12 +4 Cl 17 12 +5 Ar 18 12 +6 So as seen, the number of protons increases by one each time, though the number of electrons shielding the outer electrons remains fixed at 10 or 12 (all atoms are shielded by electron configuration 1s22s22p6, Al onwards they are also shielded by 3s2 electrons). Therefore net attraction increases, which helps to explain the general upwards trend. However, there are other factors that must be considered, which would explain the differences in increase rate as well as the two drops in energy level. The drop in energy level between Mg and Al can be explained by the introduction of a ‘p’ orbital with Al. The 3p outer electron is further away from the nucleus than 3s electrons, and also it is shielded by the 3s electrons as well as the previous 3 energy levels, both factors decreasing the ionisation energy level. As the net attraction of Al is the same as Na, this explains the relative similarity between them regarding ionisation energy level. This also applies for the similarity between Mg and Si, both with a net attraction of +2. From Al to Ar, there is the same number of energy levels, whi...