Question

explain the trends of alkali metal

Answer 1

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Describe and explain the trend in reactivity down the alkali metalsgroup. This is because the outer electron in each atom is further away from the nucleus as you go down the group and so the electrostatic forces between the nucleus and the outer electron are weaker.

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Answer 2

As their atomic numbers progress further down on the Periodic table, their atomic radius and chemical reactivity increases, while their electronegativity and heat of vaporization decreases. All Alkali Metals have an Ns1 electron configuration and all of them have a very distinctive flame color due to their outer S electron’s easy excitation.

as you go down group 1 from top to bottom, the mass of a cubic centimetre of element has a tendency to increase. 
That is, the density of group 1 elements shows a "general trend" of increasing as you go down the group from top to bottom.
the atomic radius increases down the group, the delocalised electrons making up the metallic bond get further from the nucleus so the metallic bond gets weaker and easier to weaken as you go down the group.

Usual trends are explained here...Hope U get the facts.