Electronegativity and bond polarity in covalent

• Electronegativity - the power of an atom to attract the electron density in a covalent bond towards itself
• Electron density is used to describe the way the negative charge is distributed in a molecule
• Electronegativity depends on:

  • Nuclear charge
  • Distance between nucleus and outer shell electrons
  • Shielding of the nuclear charge by inner shell electrons
• The smaller the atom, the closer the nucleus is to the shared outer main level electrons and the greater its electronegativity
• The larger the nuclear charge (for a given shielding effect) the greater the electronegativity
• Trends in electronegativity

  • Going up the periodic table, electronegativity increases (atoms get smaller) and there is less shielding by electrons in inner shells.
  • Going across the periodic table, electronegativity increases (nuclear charge increases, number of inner levels remain the same, atoms become smaller)
• Polarity of covalent bonds is about the unequal sharing of electrons between the covalently bonded atoms
• Covalent bonds between two atoms that are the same

  Both atoms have the same electronegativity and therefore a completely non-polar bond