• Electronegativity?is the ability of an atom to attract a pair of electrons towards itself in a covalent bond
• This phenomenon arises from the?positive?nucleus’s ability to attract the?negatively?charged electrons, in the outer shells, towards itself
• The?Pauling?scale?is used to assign a value of electronegativity for each atom

First three rows of the periodic table showing electronegativity values

• 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 electron density towards itself when covalently bonded to another atom

Electron distribution in the C-F bond of fluoromethane

Nuclear charge

• 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?increase?in?nuclear?attraction?for the electrons in the outer shells
• Therefore, an?increased nuclear charge?results in an?increased electronegativity

As the nuclear charge increases, the electronegativity of an element increases as well

Atomic radius

• 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

As the atomic radius increases, the nucleus has less of an attraction for the bonding electrons causing atom A to have a higher electronegativity than atom B

Shielding

• Filled?energy levels can?shield?(mask) the effect of the nuclear charge causing the outer electrons to be?less attracted?to the nucleus
• Therefore, the addition of extra?shells and subshells?in an atom will cause the outer electrons to experience?less?of the attractive force of 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

Filled inner energy levels mask the nuclear attraction from the outer bonding electrons