carbon and its compounds — Science STD 10 — Question
Gujarat BoardEnglish MediumSTD 10Sciencecarbon and its compounds4 Marks
Question
Explain the tetravalency of carbon.
✓
Answer
→ The atomic number of carbon is $6$ .
$
C _{( Z =6)}=\begin{array}{ll}
K & L \\
2 & 4
\end{array}
$
→ Hence, there are $2$ electrons in its first $( K )$ shell and $4$ in second $(L)$ shell i.e. outer most shell. Thus, carbon has $6$ . protons and $6$ electrons.
- The reactivity of an element is explained by its tendency to attain a completely filled outer shell to attain noble gas configuration.
→ Elements forming ionic compounds achieve noble gas configuration by either losing or gaining electrons from the outer most shell. The ease of carbon is different since it has $4$ electrons in its outermost shell.
→ Carbon has to either gain or lose $4$ electrons to attain noble gas configuration. The problem in doing this is discussed below :
$(1)$ Carbon can gain $4$ electrons to form $C ^{4-}$ anion. If carbon does this, it will be difficult for the nucleus with $6$ protons to hold $10$ electrons ( $6$ existing $+4$ borrowed) i.e. $4$ extra electrons.
$(2)$ Carbon can lose $4$ electrons to form $C ^{4+}$ cation. This would require a large amount of energy to remove $4$ electrons leaving behind a carbon cation with $6$ protons in its nucleus holding on to just $2$ electrons. Solution :
To overcome these problems, carbon neither accepts, nor gains but shares its valence electrons with other atoms of carbon or with atoms of other elements. The shared electrons belong to the outer shells of both the atoms. This way both the atoms attain noble gas configuration.
→ The bond formed by sharing of electrons in this manner is known as covalent bond.
→ Not only carbon but many other elements form molecules by sharing electrons and forming covalent bonds.
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