What periodic trends of reactivity occur with the alkali metals?
Alkali metals ( group one ) are highly reactive metals. All alkali metals have one electron in the outer shell. In a reaction, this electron is lost and the alkali metal forms a +1 ion. As you go down group 1, the number of electron shells increases – lithium has two, sodium has three etc. Therefore, the outermost electron gets further from the nucleus. The attraction from the positive nucleus to the negative electron is less. This makes it easier to remove the electron and makes the atom more reactive.