Polar and non polar molecules

• Define bond polarity and molecular polarity.

  Molecular polarity depends on bond polarity and the distribution of electrons in overall molecule

  Bond polarity when electrons are shared unequally between two atoms in covalent bond → more electronegative atom attracts electron more strongly

  creating partial negative charge o-

  creating partial positive charge o+

  e.g HF, flourine is more elctronegative so electrons are pulled closer to F

• Explain the role of electronegativity in determining polarity.

  Electron negativity difference Difference between atoms	Bond type
  0-0.4	Non-polar covalent
  0.5-1.7	Polar covalent
  >1.7	ionic

• Distinguish between polar and non-polar molecules based on structure and examples

  Polar molecule has uneven distribution of charge ( a dipole)

  Occurs when:

  • Molecules contain polar bonds

  • Molecular shape does not cancel out dipoles

Example: water has polar bonds and a bent shape → polar molecule

Non polar molecule

• Equal sharing of electrons

• Polar bonds that cancel each other out

Example: CO2 is linear → diapoles cancel → non-polar molecule

• Give examples of polar and non-polar covalent substances

tricks to identify symmetry

• only one type of atom = non polar e.g H2, Cl2, N2

• If it contains different atoms but evenly distributed = non polar

• If it contains different atoms it is unevenly distributed = polar e.g NH3

• Acids = polar

• hydrocarbons = non polar