9701 · 3.1
Electronegativity and bonding
Electronegativity measures how strongly an atom pulls on shared electrons in a bond. This 'tug-of-war' determines if a bond is non-polar, polar, or even ionic.
Need to know
What you need to know
- **Across a Period (e.g., Li to F):** Electronegativity increases. The number of protons in the nucleus increases, strengthening its positive pull, while the inner electron shells provide a similar level of shielding.
- **Down a Group (e.g., F to I):** Electronegativity decreases. Although nuclear charge increases, the bonding electrons are in shells further from the nucleus, and there are more inner shells causing increased shielding. These factors outweigh the increased nuclear charge.
- **Noble Gases:** These elements are typically not assigned electronegativity values as they do not readily form covalent bonds.
Explanation
The Tug-of-War for Electrons
- Electronegativity increases across a period and decreases down a group.
- A large difference in electronegativity (ΔEN) creates a polar covalent bond; a very large ΔEN leads to ionic character.
- Bond polarity contributes to intermolecular forces and affects physical properties, especially if the molecule is asymmetrical.
- Metallic and ionic bonding involve different electron models, which can be predicted using electronegativity trends.