Question

The carbon atoms in calcium carbide are held by

• A. Ionic bonds
• B. Two sigma bonds
• C. Two sigma and one coordinate bond
• D. One sigma and two $\pi$ bonds
• E. One sigma and one $\pi$ bond

Hint:

Triple bonds always consist of $1\sigma + 2\pi$, double bonds consist of $1\sigma + 1\pi$, and single bonds consist of only $1\sigma$.

Answer 1

The Correct Option is D

Concept: Calcium carbide ($CaC_2$) is an ionic compound consisting of $Ca^{2+}$ cations and $C_2^{2-}$ anions. The question focuses on the bonding specifically *within* the $C_2^{2-}$ dicarbide ion.

Step 1: {Analyze the structure of the $C_2^{2-}$ ion.}
The dicarbide ion ($[C \equiv C]^{2-}$) is isoelectronic with the Nitrogen molecule ($N_2$). To satisfy the octet and the formal charge, the two carbon atoms must be connected by a triple bond.

Step 2: {Identify the types of bonds in a triple bond.}
In a triple bond between two atoms, the first bond formed is a sigma ($\sigma$) bond (head-on overlap). The remaining two bonds are pi ($\pi$) bonds (lateral overlap of p-orbitals).

Step 3: {Conclude the bonding nature.}
Since the carbon atoms in $CaC_2$ are held together by a triple bond within the anion, they are specifically held by one sigma and two $\pi$ bonds.