a) State the Aufbau principle and use it to write the electronic configuration of the following elements: i) Calcium (Ca, Z = 20) ii) Iron (Fe, Z = 26) iii) Chlorine (Cl, Z = 17) b) i) Define the term 'ionization energy'. ii) The first ionization energies (in kJ/mol) of the elements sodium to argon are given below: Na: 496, Mg: 738, Al: 578, Si: 786, P: 1012, S: 1000, Cl: 1251, Ar: 1521 Explain why: I. The ionization energy of Al (578 kJ/mol) is lower than that of Mg (738 kJ/mol). II. The ionization energy of S (1000 kJ/mol) is lower than that of P (1012 kJ/mol). c) Distinguish between a period and a group in the periodic table, and state ONE property that increases across a period and ONE property that increases down a group.