Question

Which element has the ground-state electron configuration [Xe]6s²5d¹4f⁷?

Eu

Tb

Pt

Gd

How many valence electrons does a neutral polonium atom have?

4

6

2

84

Of the following, which atom has the largest atomic radius?

Cr

Sc

Co

Br

Of the following, which atom has the smallest atomic radius?

Po

Ba

Te

Sr

Of the following, which atom has the smallest atomic radius?

Br

K

Co

Ni

Answer 1

Answers)

i)

Gd (Gadolinium) has ground state electron configuration [Xe]6s2 5d1 4f7

Eu = [Xe] 4f7 6s2

Tb = [Xe] 4f9 6s2

Pt = [Xe] 4f14 5d9 6s1

Gd = [Xe] 6s2 5d1 4f7

ii)

Electron configuration of Polonium = [Xe] 4f14 5d10 6s2 6p4

As the outermost sub shell has 4 electrons, valency is 4.

iii)

As the atomic radius increases from top to bottom and decreases from left to right in modern periodic table.

Atomic radius order will be = Sc>Co>Br>Cr

Atomic Radius of Cr = 128 pm

Atomic Radius of Sc = 230 pm

Atomic Radius of Co = 200 pm

Atomic Radius of Br = 185 pm

So, Scandium (Sc) has highest atomic radius.

iv)

As the atomic radius increases from top to bottom and decreases from left to right in modern periodic table.

Atomic radius order will be = Te<Sr<Ba<Po

Atomic Radius of Po = 280 pm

Atomic Radius of Ba = 268 pm

Atomic Radius of Te = 210 pm

Atomic Radius of Sr = 255 pm

So, Telluriam has smalles atomic radius.

v)

As the atomic radius decreases from left to right in modern periodic table.

But, in transition elements, the number of electrons in 3d subshell will increase. Hence, Balancing the nuclear charge. So, the atomic radius will be lower.

Atomic radius order will be = K>Co>Ni>Br

Atomic Radius of Co = 200 pm

Atomic Radius of Br = 185 pm

Atomic Radius of K = 280 pm

Atomic Radius of Ni = 163 pm

So, Ni has smallest atomic radius.