What is Electronegativity?
Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond towards itself. It's a fundamental concept in chemistry that helps predict how atoms will interact and form molecules. The higher an atom's electronegativity, the stronger its pull on bonding electrons.
Key Principles and Measurement
Electronegativity is typically quantified using scales, with the Pauling scale being the most common, where fluorine (F) is assigned the highest value (3.98) and cesium (Cs) the lowest (0.79). Across the periodic table, electronegativity generally increases from left to right within a period and decreases from top to bottom within a group, due to changes in nuclear charge and atomic size.
Electronegativity in Action: The Water Molecule
Consider a water molecule (H₂O). Oxygen has a higher electronegativity (3.44) than hydrogen (2.20). This difference means that the oxygen atom pulls the shared electrons in the O-H bonds closer to itself, creating a partial negative charge on the oxygen and partial positive charges on the hydrogen atoms. This unequal sharing of electrons makes water a polar molecule.
Importance in Chemical Bonding
Electronegativity differences are critical for determining the type of chemical bond formed between atoms. Large differences (typically >1.7 on the Pauling scale) result in ionic bonds, where electrons are essentially transferred. Small differences lead to polar covalent bonds (unequal sharing), and no difference results in nonpolar covalent bonds (equal sharing). Understanding these differences helps predict molecular geometry, solubility, and reactivity.