How do the following properties charge in alkali metals?
1 atomic size
2 metallic character
3 ionization potential
4 electron affinity

Dear Student,

1. Atomic Radii
The alkali metals belong to group 1 which means that they have 1 valence electron so they posses very less amount of nuclear charge i.e attraction between nucleus(+ve) to the outermost electron is very less so they have large atomic size.
As we move down the group, the number of electron shells of the element increases by one. E.g. sodium has 3 electron shells, potassium has 4, rubidium has 5. Since the number of electron shells increase, the atom is getting larger and thus the atomic radius increases.

2. Metallic character
It depends on ionization energy. As ionization energy decide how fast a particular metal will give its electron.
The metallic character increases as you go down a group. Since the ionization energy decreases going down a group (or increases going up a group), the increased ability for metals lower in a group to lose electrons makes them more reactive.

3. Ionization potential
Alkali metals have lowest ionization potential in respective periods.
Ionization potential decreases down the group due to their atomic size being the largest in their respective periods. 
On moving down the group, the atomic size increases and the number of inner shells also increases, increasing the magnitude of screening effect and consequently, the ionization energy decreases down the group. Hence Lithium will have the highest first ionization potential out of the alkali metals. 

4. Electron affinity
Electron affinity is, essentially the opposite of the ionization energy: Instead of removing an electron from the element we add an electron to the element to create an anion.
electron affinity decreases down the group for alkali metals.

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