REACTIVITY TREND OF ALKALI METALS
REACTIVITY TREND OF ALKALI METALS.
As you go down the group from one element down to the next the atomic radius gets bigger due to an extra filled electron shell.
The outer electron is further and further from the nucleus and is also shielded by the extra full shell of negative charge, therefore the outer electron is less and less strongly held by the positive nucleus as the attractive force is decreased, and so.