Answer :
To understand why the electron affinity for nitrogen (N) is less favorable than that for carbon (C), let's examine the electronic configurations and the concept of electron affinity in detail.
### Electron Configurations
1. Carbon (C):
- Atomic number: 6
- Ground-state electronic configuration: 1s² 2s² 2p²
2. Nitrogen (N):
- Atomic number: 7
- Ground-state electronic configuration: 1s² 2s² 2p³
### Electron Affinity
Electron affinity is the energy change when an electron is added to a neutral atom in the gas phase to form a negative ion. A negative value of electron affinity indicates that energy is released when the electron is added, making the process exothermic and generally favorable.
### Explanation of Electron Affinity Trends
1. General Trend:
As you move from left to right across a period on the periodic table, electron affinity typically becomes more negative (more favorable), as atoms are more inclined to gain an electron to achieve a stable noble gas configuration.
2. Specific Observations for Carbon and Nitrogen:
- Carbon has an electron affinity of -122 kJ/mol, indicating it releases energy when it gains an electron.
- Nitrogen has an electron affinity greater than 0 kJ/mol, indicating it either requires energy to gain an electron or releases less energy compared to carbon.
### Half-Filled Stability & Electron-Electron Repulsion
- Half-Filled Stability:
Nitrogen has a half-filled p orbital (configuration: 2p³). Half-filled subshells are relatively more stable due to exchange energy and symmetrical distribution of electrons. This stability means that adding an extra electron to nitrogen would disrupt this stable configuration.
- Electron-Electron Repulsion:
When an extra electron is added to nitrogen, it goes into the already half-filled 2p orbital, resulting in increased electron-electron repulsion. This repulsion makes the process of gaining an extra electron less favorable energetically.
In contrast, carbon, with the configuration 2p², does not have the added stability of a half-filled subshell. Therefore, it does not face the same level of electron-electron repulsion when an additional electron is added. This makes carbon more willing to accept an extra electron compared to nitrogen.
### Conclusion
The less favorable electron affinity of nitrogen compared to carbon can be best explained by the half-filled stability of nitrogen's p orbitals and the increased electron-electron repulsion experienced when adding an extra electron to nitrogen. This makes the electron affinity for nitrogen less exothermic, resulting in a value greater than 0 kJ/mol, opposed to carbon which has an electron affinity of -122 kJ/mol.
### Electron Configurations
1. Carbon (C):
- Atomic number: 6
- Ground-state electronic configuration: 1s² 2s² 2p²
2. Nitrogen (N):
- Atomic number: 7
- Ground-state electronic configuration: 1s² 2s² 2p³
### Electron Affinity
Electron affinity is the energy change when an electron is added to a neutral atom in the gas phase to form a negative ion. A negative value of electron affinity indicates that energy is released when the electron is added, making the process exothermic and generally favorable.
### Explanation of Electron Affinity Trends
1. General Trend:
As you move from left to right across a period on the periodic table, electron affinity typically becomes more negative (more favorable), as atoms are more inclined to gain an electron to achieve a stable noble gas configuration.
2. Specific Observations for Carbon and Nitrogen:
- Carbon has an electron affinity of -122 kJ/mol, indicating it releases energy when it gains an electron.
- Nitrogen has an electron affinity greater than 0 kJ/mol, indicating it either requires energy to gain an electron or releases less energy compared to carbon.
### Half-Filled Stability & Electron-Electron Repulsion
- Half-Filled Stability:
Nitrogen has a half-filled p orbital (configuration: 2p³). Half-filled subshells are relatively more stable due to exchange energy and symmetrical distribution of electrons. This stability means that adding an extra electron to nitrogen would disrupt this stable configuration.
- Electron-Electron Repulsion:
When an extra electron is added to nitrogen, it goes into the already half-filled 2p orbital, resulting in increased electron-electron repulsion. This repulsion makes the process of gaining an extra electron less favorable energetically.
In contrast, carbon, with the configuration 2p², does not have the added stability of a half-filled subshell. Therefore, it does not face the same level of electron-electron repulsion when an additional electron is added. This makes carbon more willing to accept an extra electron compared to nitrogen.
### Conclusion
The less favorable electron affinity of nitrogen compared to carbon can be best explained by the half-filled stability of nitrogen's p orbitals and the increased electron-electron repulsion experienced when adding an extra electron to nitrogen. This makes the electron affinity for nitrogen less exothermic, resulting in a value greater than 0 kJ/mol, opposed to carbon which has an electron affinity of -122 kJ/mol.
