Arrange the elements in order of decreasing first ionization energy

Question:

 

 

Answer:

Question 1.

The decreasing order of first ionization energy is-

Li > Na > K > Rb

As the atomic radius increases then the removal of electrons becomes easy.

Also, the ionization energy decreases from top to bottom in groups, and increases from left to right across a period. Thus, helium has the highest first ionization energy, while francium has the lowest.

 

Question 2.

The decreasing order of first ionization energy is-

Kr > Br > As > Se > Ge > Ca > Ga > K

 

The first ionization energy of an element is the energy needed to remove the outermost electron from a neutral atom in the gas phase.

Outermost electrons for the given elements are-

Kr = 4p⁶

Br = 4p⁵

As = 4p³

Se = 4p⁴

Ge = 4p²

Ca = 4s²

Ga = 4p¹

K = 4s¹

 

As has higher first ionization energy than Se because As has stable half-filled p³ configuration.