Electronegativity and Bonding Types

Electronegativity

• Electronegativity is an atom's ability to attract the electron pair in a covalent bond towards itself.
• Measured on the Pauling scale (0 to 4).
• Fluorine is the most electronegative element (4.0).
• Increases across a period: more protons, smaller atomic radius.
• Decreases down a group: greater distance between nucleus and outer electrons, increased shielding.

Bonding Types

• Ionic and covalent bonding are extremes of a continuum.
• Electronegativity difference determines bond type.
• Small difference: purely covalent.
• Large difference (> 1.7): ionic.
• Polar covalent bond (0.3 to 1.7): unequal electron distribution, creating a dipole (δ+ δ-).

Polar and Non-polar Molecules

• Symmetrical molecules (identical bonds, no lone pairs) are non-polar.
• Individual bond dipoles cancel out due to symmetry.
• Asymmetrical molecules with polar bonds are polar (e.g., CH3Cl).
• CO2 is symmetrical and non-polar.

Intermolecular Forces

• Van der Waals Forces (also called transient, induced dipole-dipole interactions)
  • Occur between all simple covalent molecules and noble gas atoms.
  • Caused by temporary fluctuations in electron density, creating transient dipoles.
  • Strength increases with more electrons due to higher chance of temporary dipole formation.
• Permanent Dipole-dipole Forces
  • Occur between polar molecules.
  • Stronger than Van der Waals, leading to higher boiling points.
  • Polar molecules have a permanent dipole.
  • Common in molecules with C-Cl, C-F, C-Br, H-Cl, C=O bonds.
• Hydrogen Bonding
  • Strongest type of intermolecular force.
  • Occurs when H is bonded to one of the three most electronegative atoms (N, O, F).
  • Requires an available lone pair on the electronegative atom.
  • Creates a strong attraction between molecules
  • e.g., H-O-H, H-N-H, F-H