How many `sigma and pi` bonds are there in calcium cyanamide `Ca(CN)_2` ?

Options

A. `2sigma and 1pi`
B. `2 pi and 2 sigma`
C. `1 sigma and 2 pi`
D. `2 sigma and 3 pi`.

Answer

To determine the number of sigma (σ) and pi (π) bonds in calcium cyanamide (Ca(CN)₂), we can follow these steps:

### Step 1: Understand the Structure of Calcium Cyanamide
Calcium cyanamide consists of one calcium ion (Ca²⁺) and two cyanide ions (CN⁻). The cyanide ion has a carbon atom (C) bonded to a nitrogen atom (N).

### Step 2: Analyze the Cyanide Ion (CN⁻)
The cyanide ion (CN⁻) is a linear molecule. The carbon atom has four valence electrons, and the nitrogen atom has five valence electrons. Since CN⁻ has a negative charge, it means that there is an additional electron, making it a total of six electrons around nitrogen.

### Step 3: Determine Bonding in CN⁻
To satisfy the octet rule:
- Carbon needs four electrons to complete its octet.
- Nitrogen needs three electrons to complete its octet (it already has five).

To achieve this, carbon and nitrogen form a triple bond:
- One σ bond is formed by the head-on overlap of orbitals.
- Two π bonds are formed by the sidewise overlap of the remaining p orbitals.

### Step 4: Count the Bonds in CN⁻
In the cyanide ion:
- There is **1 σ bond** (from the triple bond).
- There are **2 π bonds** (from the triple bond).

### Step 5: Consider the Calcium Ion
The calcium ion (Ca²⁺) does not contribute to any covalent bonding in the molecule. It is an ionic bond with the cyanide ions.

### Step 6: Total Count of Bonds in Ca(CN)₂
Since there are two cyanide ions in calcium cyanamide:
- From the two CN⁻ ions, we have:
- **2 σ bonds** (1 from each CN⁻)
- **4 π bonds** (2 from each CN⁻)

### Final Count
Thus, in calcium cyanamide (Ca(CN)₂):
- Total σ bonds = 2
- Total π bonds = 4

### Summary
- **Total σ bonds**: 2
- **Total π bonds**: 4