electronegativity and bond polarity

• what is electro negativity ?

  • Electronegativity is the power of an atom to attract the pair of electrons in a covalent bond towards itself
• The electron distribution in a covalent bond between elements with different electronegativities will be ?

  unsymmetrical
• The electron distribution in a covalent bond between elements with different electronegativities is unsymmetrical because ?

  A phenomenon arises from the ability of the positive nucleus to attract the negatively charged electrons, in the outer shells, towards itself
• what is the most electronegative element ?

  • Fluorine is the most electronegative atom on the Periodic Table, with a value of 4.0 on the Pauling Scale
  • It is best at attracting electrons towards itself when covalently bonded to another atom
• what factors affect electronegativity ?

  • nuclear charge
  • atomic radius
  • shielding
• how does nuclear charge affect electronegativity ?

  • Attraction exists between the positively charged protons in the nucleus and negatively charged electrons found in the energy levels of an atom
  • An increase in the number of protons leads to an increasein nuclear attraction for the electrons in the outer shells
  • Therefore, an increased nuclear charge results in an increased electronegativity
• how does atomic radius affect electronegativity ?

  • The atomic radius is the distance between the nucleus and electrons in the outermost shell
  • Electrons closer to the nucleus are more strongly attracted towards its positive nucleus
  • Those electrons further away from the nucleus are less strongly attracted towards the nucleus
  • Therefore, an increased atomic radius results in a decreased electronegativity
• how does shielding affect electronegativity ?

  • Filled energy levels can shield (mask) the effect of the nuclear charge causing the outer electrons to be less attracted to the nucleus
  • Sodium (period 3, group 1) has higher electronegativity than caesium (period 6, group 1) as it has fewer shells and therefore the outer electrons experience less shielding than in caesium
  • Thus, an increased number of inner shells and subshells will result in a decreased electronegativity
  • Electronegativity varies across periods and down the groups of the periodic table
• how does electronegativity change going down a group ?

  • There is a decrease in electronegativity going down the group
  • The nuclear charge increases as more protons are being added to the nucleus
  • However, each element has an extra filled electron shell, which increases shielding
  • The addition of the extra shells increases the distance between the nucleus and the outer electrons resulting in larger atomic radii
  • Overall, there is decrease in attraction between the nucleus and outer bonding electrons
• how does electronegativity change across a period ?

  • Electronegativity increases across a period
  • The nuclear charge increases with the addition of protons to the nucleus
  • Shielding remains relatively constant across the period as no new shells are being added to the atoms
  • The nucleus has an increasingly strong attraction for the bonding pair of electrons of atoms across the period of the periodic table
  • This results in smaller atomic radii
• what makes a bond polar and non-polar ?

  • When two atoms in a covalent bond have the same electronegativity the covalent bond is nonpolar
  • When two atoms in a covalent bond have different electronegativities the covalent bond is polar and the electrons will be drawn towards the more electronegative atom
• what is the result of a colorant bond being polar ?

  • The negative charge centre and positive charge centre do not coincide with each other
  • This means that the electron distribution is asymmetric
  • The less electronegative atom gets a partial charge of δ+ (delta positive)
  • The more electronegative atom gets a partial charge of δ- (delta negative)
  • The greater the difference in electronegativity the more polar the bond becomes
• what is the dipole moment ?

  • The dipole moment is a measure of how polar a bond is
  • The direction of the dipole moment is shown by the following sign in which the arrow points to the partially negatively charged end of the dipole