Alkali metals have high difference in the first and second ionisation energy as they achieve stable noble gas configuration after first ionisation.
22.
The electronic states $$X$$ and $$Y$$ of an atom are depicted below :
$$\eqalign{
& X:1{s^2}2{s^2}2{p^6}3{s^1} \cr
& Y:1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1} \cr} $$
Which of the following statements is not correct?
A
$$X$$ represents an alkali metal.
B
More energy is required to remove an electron from $$X$$ than from $$Y.$$
C
$$Y$$ represents ground state of the element.
D
Less energy is required to remove an electron from $$X$$ than from $$Y.$$
Answer :
Less energy is required to remove an electron from $$X$$ than from $$Y.$$
Due to small size of atom $$X\left( {n = 3} \right)$$ than $$Y\left( {n = 4} \right),$$ the electron present in $$3{s^1}$$ orbital is more attracted towards the nucleus. Hence, greater amount of energy is required for the removal of this valence electron from $$X$$ as compared to $$Y.$$
23.
To which group, an element with atomic number 88 will belong?
NOTE: Electronegativity increases on moving from left to right in a period and decreases on moving from top to bottom in a group.
$$Si$$ and $$P$$ are placed in the $${3^{{\text{rd}}}}$$ period while $$C$$ and $$N$$ are placed in the $${2^{{\text{nd}}}}$$ period. Elements in $${2^{{\text{nd}}}}$$ period have higher electronegativities than those in the $${3^{{\text{rd}}}}$$ period. Since $$N$$ has smaller size and higher nuclear charge than $$C,$$ its electronegativity is higher than that of $$C.$$ Similarly, the electronegativity of $$P$$ is higher than that of $$Si$$ . Thus, the overall order is : $$Si,P,C,N.$$
25.
Fill in the blanks with appropriate option.
The ability of an atom to attract shared electrons to itself is called $$\underline {\left( {\text{i}} \right)} .$$ It is generally measured on the $$\underline {\left( {{\text{ii}}} \right)} $$ scale. An arbitrary value of $$\underline {\left( {{\text{iii}}} \right)} $$ is assigned to fluorine ( have greatest ability to attract electrons ). It generally $$\underline {\left( {{\text{iv}}} \right)} $$ across a period and $$\underline {\left( {\text{v}} \right)} $$ down a group.
Elements $$X, Y, Z$$ with atomic numbers $$19, 37, 55$$ lie in group 1 (alkali metals). On moving down a group from the size of atoms increases, the outermost electrons become less strongly held. So the ionization energy decreases. Therefore, $$IE$$ of $$Y$$ could be between those of $$X$$ and $$Z.$$
\[\begin{matrix}
{} \\
{} \\
I.E. \\
\end{matrix}\,\,\,\begin{matrix}
X \\
K\left( 19 \right) \\
4.3 \\
\end{matrix}\,\,\,\begin{matrix}
Y \\
Rb\left( 37 \right) \\
4.2 \\
\end{matrix}\,\,\,\begin{matrix}
Z \\
Cs\left( 55 \right) \\
3.9 \\
\end{matrix}\]
28.
In which of the following, the order is not in accordance with the property mentioned.
29.
The formation of the oxide ion $$O_{\left( g \right)}^{2 - }$$ requires first an exothermic and then an endothermic step as shown below
$$\eqalign{
& {O_{\left( g \right)}} + {e^ - } = O_{\left( g \right)}^ - \,\,\Delta {H^ \circ } = - 142\,kJmo{l^{ - 1}} \cr
& {O^ - }\left( g \right) + {e^ - } = O_{\left( g \right)}^{2 - }\,\,\Delta {H^ \circ } = 844\,kJmo{l^{ - 1}} \cr} $$
This is because
A
$${O^ - }$$ on will tend to resist the addition of another
electron
B
Oxygen has high electron affinity
C
Oxygen is more elecronegative
D
$${O^ - }$$ ion has comparatively larger size than oxygen atom
Answer :
$${O^ - }$$ on will tend to resist the addition of another
electron
$${O^ - }$$ ion exerts a force of repulsion on the incoming electron. The energy is required to overcome it.
30.
Why is the electron gain enthalpy of $$O$$ or $$F$$ less than that of $$S$$ or $$Cl?$$
A
$$O$$ and $$F$$ are more electronegative than $$S$$ and $$Cl.$$
B
When an electron is added to $$O$$ or $$F,$$ it goes to a smaller $$\left( {n = 2} \right)$$ level and suffers more repulsion than the electron in $$S$$ or $$Cl$$ in larger level $$\left( {n = 3} \right).$$
C
Adding an electron to $$3p$$ -orbital leads to more repulsion than $$2p$$ -orbital.
D
Electron gain enthalpy depends upon the electron affinity of the atom.
Answer :
When an electron is added to $$O$$ or $$F,$$ it goes to a smaller $$\left( {n = 2} \right)$$ level and suffers more repulsion than the electron in $$S$$ or $$Cl$$ in larger level $$\left( {n = 3} \right).$$