The number of unpaired electrons in "CN" depends on whether the question refers to the neutral cyanogen radical (CN) or the cyanide ion (CN-). These are distinct chemical species with different electron counts and magnetic properties.
- The cyanogen radical (CN) contains one unpaired electron.
- The cyanide ion (CN-) contains zero unpaired electrons.
Understanding Electron Configuration in Diatomic Species
To determine the number of unpaired electrons, we use the principles of Molecular Orbital (MO) theory. This theory describes how atomic orbitals combine to form molecular orbitals, which electrons then occupy. Electrons fill these molecular orbitals following Hund's rule and the Pauli exclusion principle, similar to atomic orbitals.
Cyanogen Radical (CN)
The cyanogen radical (CN) is a neutral species.
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Total electrons: Carbon (C) has 6 electrons, and Nitrogen (N) has 7 electrons. Thus, the CN radical has a total of 6 + 7 = 13 electrons.
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Molecular Orbital Configuration: For diatomic molecules like CN, the 13 electrons fill the molecular orbitals in increasing order of energy:
- σ2s (2 electrons)
- σ*2s (2 electrons)
- π2p (4 electrons)
- σ2p (2 electrons)
- π*2p (3 electrons)
In the π*2p molecular orbital, there are two degenerate orbitals. According to Hund's rule, electrons will occupy these degenerate orbitals singly before pairing up. Therefore, the last three electrons (11th, 12th, and 13th) would fill one π2p with 2 electrons, and the next (13th) electron would go into one of the π*2p orbitals, leaving one of the degenerate π*2p orbitals with a single electron.
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Unpaired Electrons: This results in one unpaired electron in the π*2p orbital.
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Magnetic Property: Due to the presence of an unpaired electron, the cyanogen radical (CN) is paramagnetic, meaning it is attracted to a magnetic field.
Cyanide Ion (CN-)
The cyanide ion (CN-) is an anion with a -1 charge.
- Total electrons: Carbon (C) has 6 electrons, Nitrogen (N) has 7 electrons, and the -1 charge adds 1 electron. Thus, the CN- ion has a total of 6 + 7 + 1 = 14 electrons.
- Molecular Orbital Configuration: For diatomic molecules with 14 electrons (isoelectronic with N₂), the molecular orbital configuration is:
- σ2s (2 electrons)
- σ*2s (2 electrons)
- π2p (4 electrons)
- σ2p (2 electrons)
- All these orbitals are fully occupied by paired electrons. There are no electrons in the higher-energy π*2p orbitals.
- Unpaired Electrons: All 14 electrons in the cyanide ion are paired, meaning there are zero unpaired electrons.
- Magnetic Property: Because it has no unpaired electrons, the cyanide ion (CN-) is diamagnetic, meaning it is weakly repelled by a magnetic field.
Summary Comparison: CN vs. CN-
The table below summarizes the key differences in electron count and magnetic properties for the cyanogen radical and the cyanide ion:
| Species | Total Electrons | Unpaired Electrons | Magnetic Property |
|---|---|---|---|
| CN (Radical) | 13 | 1 | Paramagnetic |
| CN- (Ion) | 14 | 0 | Diamagnetic |
In conclusion, the neutral cyanogen radical (CN) has one unpaired electron, making it paramagnetic, while the cyanide ion (CN-) has no unpaired electrons, making it diamagnetic.
