Question

The trend in atomic radii on moving down the group, with reference to the alkali metals in group 1.
A.Increases
B.Decreases
C.Remain constant
D.None of these

Answer 1

Hint: The group 1 metals are known as alkali metals as they form metal hydroxides which are alkaline in nature and thus are known as alkali metals. They are highly reactive metals. We know that as we move down the group the reactivity increases and the size of the elements increases. The number of valence electrons remains the same.

Complete answer:
- The six metals of the periodic table lying in group 1 are known as alkali metals. They are highly reactive and are kept under oil to protect them from reacting with air or water. These group 1 elements form metal hydroxides which are alkaline in nature and thus, these elements are known as alkali metals. These are very soft metals: sodium metal and potassium metal are so soft that they can be cut by a butter knife.
- These group one elements contain hydrogen, lithium, sodium, potassium, rubidium, cesium and francium. These metals have low ionization energy and have low melting points. The reactivity of these metals increase as we move down the group. Their high reactive behaviour is due to the presence of just one electron in their valence shell which they can give up readily to attain noble gas configuration.
- As we move down the group the valence electrons of the elements remain the same but the number of electrons and shells increases. The electrons in the outermost shell have the same effective nuclear charge but as we move down the shells increase and thus, the size of the elements increases and the electrons are found farther away from the nucleus. Therefore, the atomic radii increases down the group.

So, option A is correct.

Note:
When we burn lithium salts they give intense red shade which are used in fireworks. Sodium is used in various household products like common salt, baking soda and others. Rubidium burns with a purple colour and it reacts readily with oxygen and thus, is used in vacuum tubes. Francium is a very unstable metal and is very rarely found.