The first ionisation energies of elements show periodic trends across periods and groups in the periodic table.
Using the first ionisation energy of potassium, K\text{K}K, as 419 kJ mol−1419\text{ kJ mol}^{-1}419 kJ mol−1, calculate the energy required to form one K+(g)\text{K}^+(\text{g})K+(g) ion from one K(g)\text{K}(\text{g})K(g) atom. Give your answer in kJ\text{kJ}kJ, in standard form, and to two significant figures. (Avogadro constant, NA=6.02×1023 mol−1N_A = 6.02 \times 10^{23}\text{ mol}^{-1}NA=6.02×1023 mol−1)
Explain why the first ionisation energies of argon, Ar\text{Ar}Ar, and calcium, Ca\text{Ca}Ca, are both higher than the first ionisation energy of potassium, K\text{K}K.
Explain why the first ionisation energy of calcium, Ca\text{Ca}Ca, is higher than that of gallium, Ga\text{Ga}Ga.
