Electronegativity and Polarity

• What is electronegativity?

  The ability of atoms to attract electrons
• How does electronegativity relate to a covalent bond?

  It measures an atom's ability to attract shared electrons
• Which element is the most electronegative?

  Fluorine
• What scale is electronegativity measured on?

  The Pauling scale
• What does a higher value on the Pauling scale indicate?

  The atom is more electronegative
• What factors influence the electronegativity of an atom?

  • Atomic radius
  • Nuclear charge
  • Shielding
• How does atomic radius affect electronegativity?

  Smaller atoms are more electronegative
• Why do smaller atoms have higher electronegativity?

  Electrons are closer to the nucleus
• How does nuclear charge affect electronegativity?

  Higher charge increases electronegativity
• How does shielding affect electronegativity?

  Shielding reduces electronegativity
• What two trends in electronegativity are clear in the periodic table?

  Across periods and down groups
• How does electronegativity change across a period?

  Electronegativity increases across a period
• Why does electronegativity increase across a period?

  Radius decreases, nuclear charge increases
• What dominates the increase in electronegativity across a period?

  Increasing nuclear charge
• How does electronegativity change down a group?

  Electronegativity decreases down a group
• What factors cause the decrease in electronegativity down a group?

  Increased radius and shielding
• What weakens electrostatic attraction down a group?

  Distance and greater shielding
• What gives rise to polar bonds?

  Electronegativity differences
• How do electronegativity differences cause polar bonds?

  Unequal sharing of electrons
• What is a dipole?

  Separation of positive and negative charges
• In a polar bond, what charge does the more electronegative atom acquire?

  A slight negative charge (δ-)
• In a polar bond, what charge does the less electronegative atom acquire?

  A slight positive charge (δ+)
• How does electronegativity difference affect bond polarity?

  The bigger the difference, the more polar
• What type of bond exists in H2 and Cl2?

  Non-polar
• Why are bonds in H2 and Cl2 non-polar?

  Electrons are shared equally
• What type of bond exists between carbon and hydrogen?

  Essentially non-polar
• Why are C-H bonds essentially non-polar?

  Even electron distribution
• What determines the overall polarity of a molecule?

  Arrangement of polar bonds in 3D
• Why is CCl4 non-polar despite having polar bonds?

  Dipoles cancel out due to symmetry
• Why is CHCl3 polar?

  Asymmetric arrangement prevents dipoles cancelling
• How do you determine if a molecule has an overall dipole?

  Visualise 3D structure, assess dipole cancellation
• What can electronegativity differences predict?

  Bond type
• When does a pure covalent bond occur?

  Electronegativity difference is zero
• How does the bond become as electronegativity difference increases?

  More polar covalent
• What type of bond exists in HCl?

  Polar covalent
• When is a bond considered ionic?

  Electronegativity difference is very large
• What happens to electrons in an ionic bond?

  Electrons are effectively taken
• What type of bond exists in NaCl?

  Ionic
• What character do most compounds exhibit?

  A mix of ionic and covalent
• On what does the strength of electrostatic attraction between the nucleus and electrons depend?

  Nuclear charge and distance