Na and K belong to group 1 in the periodic table of elements.
(a) Explain why, in terms of their electronic configurations, potassium is more reactive than sodium.
(b) Write the balanced equation for the reaction of sodium with water.
(a) Sodium electron configuration is 1s22s22p63s1. Potassium has the electron configuration 1s22s22p63s23p64s1 rather than the expected 1s22s22p63s23p63d1. Potassium has a larger average atomic radius (220 pm) than sodium does (180 pm). The potassium atom has an extra electron shell compared to the sodium atom, which means its valence electrons are further from the nucleus, giving potassium a larger atomic radius. Potassium valence electron is at a greater distance from the attractive nucleus and is so removed more easily than sodium valence electron. As it is removed more easily, it requires less energy, and can be said to be more reactive.
(b) 2Na + 2H2O → 2NaOH + H2