Question

What is the specific property of alkali metals in periodic table:
(A) Lowest ionisation energy
(B) Smallest size
(C) Lowest electro-positivity
(D) Highest electronegativity

Answer 1

Hint : In the period when we move from left to right atomic size decreases as effective attraction increases. Results in increase in electronegativity and increase in ionisation enthalpy.

Complete Step By Step Answer:
When we move top to bottom in periodic table following changes occur;
- Atomic size increases
- Ionisation enthalpy decreases
- Metallic character increases
- electron - gain enthalpy
And when we move from left to right in periodic table following changes will occur:
-Atomic size decreases
-Ionisation enthalpy increases
-Metallic character decreases
-Electron gain enthalpy increases
Alkali metals are the first group elements with following properties:
-Largest atomic size in respective period
-Lowest ionisation enthalpy in the period
-Maximum metallic character in a period
-Lowest electron gain enthalpy
-Most electropositive elements
-Readily oxides to form compound
-Highest oxidation potential
-These are low densities elements
They are most reactive elements that they can react even in air with moisture so they must be stored under oil to keep air and water away from them
. These elements form an alkaline solution with water hence are known as alkaline metals.
As per given in the question –Option (A) is correct because due to the biggest size they have lowest ionisation energy.

Note :
Hydrogen shows similar properties with group $(1)$ alkali metals and group $(17)$ halogen so As it can lose one electron and act as alkali metals and can gain one electron to act as halogen so It is separately placed on the top of the table.