Why is iron hard and sodium is soft, yet they are both metals?

Sodium is an alkali metal and is very soft and can cut through knife while iron is a transition metal which is very hard and requires great energy to break apart.Iron is hard, tough and strong compared with sodium because of the strong metallic atom-atom .The strong attractive force between the atoms is only weakened at high temperatures; hence iron has the high melting points and boiling points.This strong bonding between atoms holding them together in iron gives it high . For example: iron has a density of ##7.9 g/(cm)^3 ##and sodium has a density of ##0.97 g/(cm)^3## (less than water hence floats on water)</p>