Why is an alkali metal so reactive?

Answer 1

Bohr's model of the atom explains the reactivity of group 1 metals, as it applies the rule that electrons are in fixed orbits, and that the shells fill up from the centre. If each shell is full it can't take any more electrons so for an electron to migrate into an already full shell another electron must take its place. This means that there will always be one electron on the outside until it undergoes ionic bonding with a non-metal and becomes a stable positive ion.

Answer 2

Atoms are stable with a full shell of electrons, so the alkali metals only need to lose one electron to get a full shell, so they are very reactive. Moreover the reactivity increases as you go down the group as the electron you lose is further from the positive nucleus attracting it. This is shielded by the electrons in between. This makes it easier for the outer electron to be lost.

Alkali metals have free unpaired electrons in their valance energy level on the bohr diagram. They're reactive because the unpaired electrons want to gain electrons so that they'll be stable and in pairs.

If you look at the Bohr model of say Lithium, which is an alkali metal, you would see that Lithium only has one valence electron (electron on outermost ring). Since it only has to give away one electron to become stable, that makes it highly reactive (the less electrons you have the less you need to give away, so you are not willing to take any and instead you want to give them away).

Answer 3

Alkali metals are so reactive because they have one lone valence electron that they want to get rid of in order to become isoelectronic with the noble gases.