Electronegativity is about how strongly an atom attracts shared electrons when it bonds with another atom.
Key Points:
Importance:
- Electronegativity helps predict what kind of bond will form between two atoms and how polar (unevenly charged) a molecule will be.
Electronegativity Scale:
- The Pauling scale is used to measure electronegativity.
- Fluorine (F) is the most electronegative element with a value of 4.0.
- Cesium (Cs) is the least electronegative with a value of 0.7.
Trends:
- Increases across a period: Electronegativity goes up as you move from left to right across a row on the periodic table. This is because atoms on the right have more protons, which attract electrons more strongly.
- Decreases down a group: Electronegativity goes down as you move down a column. This is because the outermost electrons are farther from the nucleus in larger atoms, so the pull is weaker.
Impact on Bonding:
- Nonpolar covalent bond: If two atoms have almost the same electronegativity, they share electrons equally, like in an H2 molecule.
- Polar covalent bond: If there's a moderate difference in electronegativity, the more electronegative atom pulls the electrons more, creating a polar covalent bond, like in an H2O molecule.
- Ionic bond: If the difference in electronegativity is large, one atom can take electrons from the other, forming an ionic bond, like in a NaCl molecule.
By knowing about electronegativity, chemists can predict how molecules will behave and bond with each other.
