Question

explain the trend of ionization energy across the period and down the group on the periodic table

Answer 1

The first ionisation energy is the energy required to remove the most loosely held electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+. Ionization energy decreases down a group because the number of protons as well as electrons electrons occupied in new subshells, distance from the nucleus increase and shielding effect by inner electrons increases decreasing ionisation energy. I.E Increases across a period because electrons are occupied withing the same energy level and shielding effect remains the same as well as the distance. therefore electrons are is a greater attraction force and would require a greater I.E