CBSE 2025 · Region 5 · Set 1 · Q37 · 4 marks
The combining capacity of various elements depends on the number of valence electrons. Also the reactivity of elements is explained as their tendency to attain a completely filled outer shell, that is, to attain a noble gas configuration. This may be either through gain of electrons or loss of electrons or sharing of electrons.(a)An element A has atomic number $\displaystyle 16$, how will it attain its nearest noble gas configuration ?(b)Write the number of (i) single and (ii) double covalent bonds in a molecule of butene $\displaystyle \left(\mathrm{C}_{4} \mathrm{H}_{8}\right)$.(c)Explain the formation of a molecule of ammonia $\displaystyle \left(\mathrm{NH}_{3}\right)$, using electron dot structure. (Atomic number of nitrogen is $\displaystyle 7$)(B)Why does carbon share its valence electrons with other atoms of carbon or with atoms of other elements ?
The combining capacity of various elements depends on the number of valence electrons. Also the reactivity of elements is explained as their tendency to attain a completely filled outer shell, that is, to attain a noble gas configuration. This may be either through gain of electrons or loss of electrons or sharing of electrons.
(a)
An element A has atomic number $\displaystyle 16$, how will it attain its nearest noble gas configuration ?
(b)
Write the number of (i) single and (ii) double covalent bonds in a molecule of butene $\displaystyle \left(\mathrm{C}_{4} \mathrm{H}_{8}\right)$.
(c)
Explain the formation of a molecule of ammonia $\displaystyle \left(\mathrm{NH}_{3}\right)$, using electron dot structure. (Atomic number of nitrogen is $\displaystyle 7$)
(B)
Why does carbon share its valence electrons with other atoms of carbon or with atoms of other elements ?
Marking-scheme solution
(a) It shall gain or share $\displaystyle 2$ electrons to attain its nearest noble gas configuration.
(b) (i) The number of single covalent bonds- $\displaystyle 10$
(ii) The number of double covalent bonds-$\displaystyle 1$
(c) (A)
OR
(B) Carbon cannot gain or lose $\displaystyle 4$ electrons to complete its octet as a large amount of energy is involved. /
(i) It could gain four electrons forming \(\displaystyle \mathrm{C}^{4-}\) anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons.
(ii) It could lose four electrons forming \(\displaystyle \mathrm{C}^{4+}\) cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.
Carbon and its CompoundsCovalent Bonding in Carbon CompoundsApplycase_studymedium
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CBSE Class 10 Science past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.