CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.3.1 Electronegativity

Electronegativity: Definition

  • 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

Chemical Bonding Electronegativity of Elements, downloadable AS & A Level Chemistry revision notes

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

Chemical Bonding Electronegativity of Fluorine, downloadable AS & A Level Chemistry revision notes

Electron distribution in the C-F bond of fluoromethane

Electronegativity: Affecting Factors

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

Chemical Bonding Nuclear Charge & Electronegativity, downloadable AS & A Level Chemistry revision notes

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

Chemical Bonding Atomic Radius & Electronegativity, downloadable AS & A Level Chemistry revision notes

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

Chemical Bonding Shielding & Electronegativity, downloadable AS & A Level Chemistry revision notes

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

 

Exam Tip

The nuclear charge, atomic radius and shielding are all linked to each other.

As nuclear charge increases, the nucleus has a greater attractive force on the electrons in shells given that the shielding doesn’t increase.

As a result of this, the atomic radius decreases.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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