a.) What is the definition of ionisation energy? b.) Explain trends in ionisation energy within the periodic table

a.) Ionisation energy is the energy required to remove the most loosely bound electron from an element.b.) Ionisation energy decreases down a group due to increasing electron shielding, this decreases the nuclear charge between the outer bound electron and nucleus hence decreasing the electrostatic attraction. Across a period, the ionisation energy increases due to an increase in the number of electrons hence increasing the electrostatic attraction between nucleus and electrons.