Question

An element with atomic numbers $29$ belongs to:
A. $s -$block
B. $d -$block
C. $p -$block
D. $f -$block

Answer 1

Atomic number of an element is defined as the unit positive charge present in the nucleus i.e. number of protons. The distribution of electrons in various subshells of an atom is called its electronic configuration. The location of any element in the periodic table is reflected by the quantum number of the last orbital filled in an atom.

Complete step by step solution:
The electronic configuration of the element with atomic number ${\text{29}}$is written as,
${\text{X}}{}_{{\text{29}}}$=${\text{1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{6}}}{\text{4}}{{\text{s}}^{\text{1}}}{\text{3}}{{\text{d}}^{{\text{10}}}}$
Now, its obvious from the electronic configuration that the last electron enters in d-orbital so it belongs with d-block. d-block elements are also called transition elements but this is not because its d-orbitals are fully filled so it will behave like a normal metal.
So, the above element with atomic number$29$belongs to d-block. The d-block elements are the elements of group $3$to$12$in the centre of the periodic table between $s -$block and $p -$block elements. These are characterised by filling of inner $d -$orbitals by electrons and therefore referred to as $d -$block elements. These elements have the general outer electronic configuration$\left( {n - 1} \right){d^{1 - 10}}n{s^{0 - 2}}$. They are called metals. They generally form coloured complexes. Exhibit variable oxidation states, paramagnetic behaviour and used as a catalyst. The $d -$block elements can also be called as transition elements because of forming a bridge between the chemically active elements of $s -$block and less active elements of ${13^{th}}$and ${14^{th}}$group of $p -$block.

Hence, the correct option is (B).

Note: One of the most important thing is that the $d -$block elements $Zn,{\text{ Cd,}}$and $Hg$ do not show most of the properties of transition elements due to electronic configuration$\left( {n - 1} \right){d^{1 - 10}}n{s^2}$. Hence, sometimes called pseudo transition elements. The d-block elements form many compounds out of which an important class is coordination compounds.