Match the following columns: Column I Column II (i) Most electronegative (a) Lithium (ii) Highest ionisation enthalpy (b) Caesium (iii) Least electronegative (c) Helium (iv) Lowest electron affinity (d) Fluorine

Fluorine has highest electronegativity, it is a halogen. Helium has highest ionisation enthalpy in periodic table, it has two electrons in its shell, which is attracted by the nucleus and more energy is required to remove this electron. The lowest electronegative element is caesium. The lowest electron affinity is for lithium because lithium has only one valence electron and it is easy to remove that. Column I Column II (i) Most electronegative (d) Fluorine (ii) Highest ionisation enthalpy (c) Helium (iii) Least electronegative (b) Caesium (iv) Lowest electron affinity (a) Lithium

Give a reason for the following. Ionisation potential increases across a period, from left to right.

Across a period atomic size decreases and nuclear charge increases, hence more energy is required to remove the valence electrons. Therefore, ionisation potential increases. Thus, the ionisation energy decreases from top to bottom in groups and increases from left to right across a period in the periodic table.