Question

From the elements $\mathrm{Li},\mathrm{K},\mathrm{Mg},\mathrm{C},\mathrm{Al},$ and $\mathrm{S}$, identify the

(A) Elements belonging to the same group.

(B) The element which has the tendency to lose two electrons.

(C) The element which prefers sharing of electrons to complete its octet.

(D) Most metallic element.

(E) The element that forms acidic oxide.

(F) The element that belongs to group 13.

Answer 1

Periodic table

1. The periodic table is the tabular display of the chemical elements.
2. The elements arranged in vertical columns in the periodic table are called ‘groups’.
3. The elements arranged in horizontal rows in the table are called periods.

(A) The elements belonging to the same group:

• The electronic configuration of $\mathrm{Li}$ (the atomic number is $3$) is $1{\mathrm{s}}^{2}2{\mathrm{s}}^1$.
• The electronic configuration of $\mathrm{K}$(the atomic number is $19$) is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^1$.
• The s-block elements with one electron in their s-orbital are called group one or alkali metals.
• Lithium ($\mathrm{Li}$), sodium ($\mathrm{Na}$), potassium ($\mathrm{K}$), rubidium ($\mathrm{Rb}$), caesium ($\mathrm{Cs}$), and francium ($\mathrm{Fr}$) are group 1 elements (alkali metals).
• Therefore, Lithium ($\mathrm{Li}$) and potassium ($\mathrm{K}$) are the same group elements.

(B) The element which has the tendency to lose two electrons:

• The electronic configuration of $\mathrm{Mg}$ (the atomic number is $12$) is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$.
• A magnesium atom must lose two electrons to get the same number of electrons as the nearest noble gas, neon $\mathrm{Ne}$ (atomic number$10$).
• Thus, a magnesium atom will form a ${\mathrm{Mg}}^{2+}$by losing two electrons.
• Therefore, the element which has the tendency to lose two electrons is $\mathrm{Mg}$.

(C) The element which prefers sharing of electrons to complete its octet:

• A carbon atom neither loses its four valence electrons nor gains four electrons from other atoms.
• So the carbon atom completes its octet only by sharing its outermost shell electrons with other atoms.
• Therefore, the element which prefers sharing of electrons to complete its octet is $\mathrm{C}$.

(D) The most metallic element:

• Metallic character refers to the level of reactivity of metal, that is how easily an element can lose electrons in a reaction.
• Metallic character decreases from left to right across the period as the outer electrons experience increasing effective nuclear charge and thus require more energy for their removal.
• Metallic character increases down the group as the outer electrons are further from the nucleus and require less energy for their removal.
• Potassium is in the fourth period and it is an alkali metal with atomic number 19 with an electronic configuration is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^1$.
• Here, potassium can remove the outermost electron easily since the outer electrons are further from the nucleus and require less energy for their removal.
• Therefore, potassium ($\mathrm{K}$) is the most metallic element.

(E) The element that forms acidic oxide:

• The nature of oxides whether it is acidic or basic can be found after treatment of the oxide with water.
• An acidic oxide is an oxide that produces an acidic solution upon addition to water.
• Generally the metal oxides on treatment with water form metal hydroxides which are basic in nature
• Sulphur dioxide$\left({\mathrm{SO}}_2\right)$ on treatment water gives ${\mathrm{H}}_2{\mathrm{SO}}_3$.

$\underset{\mathrm{Sulphur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\rightleftharpoons \underset{\mathrm{Sulphurous}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_3\left(\mathrm{aq}\right)}$

• Therefore, the element that forms acidic oxide is $\mathrm{S}$.

(F) The element that belongs to group 13:

• The group 13 elements are boron ($\mathrm{B}$), aluminum ($\mathrm{Al}$), gallium ($\mathrm{Ga}$), indium ($\mathrm{In}$), thallium ($\mathrm{Tl}$), and nihonium ($\mathrm{Nh}$)
• Therefore, the element belonging to group 13 is$\mathrm{Al}$.