Embibe Experts Solutions for Chapter: Classification of Elements and Periodicity in Properties, Exercise 2: Level 2

The amount of energy released when a neutral isolated gaseous atom accepts an electron to form gaseous anion is called electron
affinity.

${\mathrm{O}}_{\left(\mathrm{g}\right)}+e^{\ominus }\stackrel{\mathrm{Exothermic}}{⟶}{\mathrm{O}}_{\left(\mathrm{g}\right)}^{\ominus }$  .... (i)

${\mathrm{O}}_{\left(\mathrm{g}\right)}^{\ominus }+e^{\ominus }\stackrel{ \mathrm{Endothermic}}{⟶}{\mathrm{O}}_{\left(\mathrm{g}\right)}^{2-}$ .... (ii)

In (2) the energy has to be supplied for addition of second electron due to repulsion between an anion and extra electron. The members of third period have higher electron affinity value than members of second period.

Which process involves the maximum release of energy?

The ionization energy of ${\mathrm{He}}^{+}$ is $19.6\times {10}^{-18} \mathrm{J} {\mathrm{atom}}^{-1}.$ The energy of the first stationary state $(\mathrm{n}=1)$ of ${\mathrm{Li}}^{2+}$ is:

The energy of an electron in a hydrogen-like is given by ${\mathrm{E}}_{\mathrm{n}}=-\left(2.18\times {10}^{-18}\right)\left(\frac{{\mathrm{Z}}^2}{{\mathrm{n}}^2}\right).$

Whereas: $\mathrm{n}$ is the principal quantum number and $\mathrm{Z}$ is the atomic number of the element.

The ionization energy (in $\mathrm{kJ} {\mathrm{mol}}^{-1}$) of the ${\mathrm{Li}}^{2+}$ ion is

The total number of s-electrons in ${}_{19}\mathrm{K}$ is --------.

Atomic numbers of some elements are given below. The number of elements from the following that will be placed in group $2$ of the modern periodic table is________.

$3, 4, 7, 12, 18, 20, 26, 32, 38$

Among the following elements, how many of them are transition elements? $\mathrm{Zr}, \mathrm{Sr}, \mathrm{S}, \mathrm{V}, \mathrm{Mn}, \mathrm{Os}, \mathrm{Ce}, \mathrm{Cs}, \mathrm{Hf}, \mathrm{Fe}$________.

The number of elements from the following which have valence electron(s) in the $\mathrm{M}$-shell is_______.

$\mathrm{Si}, \mathrm{C}, \mathrm{N}, \mathrm{Be}, \mathrm{Al}, \mathrm{S}, \mathrm{F}, \mathrm{B}, \mathrm{Li}, \mathrm{Mg}, \mathrm{O}, \mathrm{Ar}$

How many of the following elements are more electronegative than Boron.

(i) $\mathrm{H}$ (ii) $\mathrm{Li}$ (iii) $\mathrm{Be}$ (iv) $\mathrm{C}$ (v) $\mathrm{N}$ (vi) $\mathrm{O}$ (vii) $\mathrm{F}$