Electronegativity & Bond Polarity | A-level Chemistry | OCR, AQA, Edexcel

Introduction

This tutorial will guide you through the concepts of electronegativity and bond polarity, essential topics in A-level Chemistry. Understanding these concepts is crucial for predicting how atoms interact in chemical bonds and the resulting molecular properties.

Step 1: Understand Electronegativity

• Electronegativity is the measure of an atom's ability to attract and hold onto electrons in a covalent bond.
• It is quantified on the Pauling Scale, developed by chemist Linus Pauling.
• Key points:
  • Higher electronegativity indicates a stronger attraction for electrons.
  • Fluorine is the most electronegative element, serving as a reference point.

Step 2: Measure Electronegativity

• The Pauling Scale provides numerical values for electronegativity.
• Common values include:
  • Fluorine (4.0)
  • Oxygen (3.5)
  • Chlorine (3.0)
  • Hydrogen (2.1)

Step 3: Recognize Trends in Electronegativity

• Electronegativity increases:
  • Across a period (from left to right)
  • Up a group (from bottom to top)
• Reasons for trends:
  • Across a period:
    • Increased nuclear charge (more protons) enhances the attraction for electrons.
  • Up a group:
    • Increased distance from the nucleus (more electron shells) reduces attraction.

Step 4: Identify Polar Bonds

• A polar bond occurs when two atoms with different electronegativities form a bond.
• Example: In a bond between chlorine (3.0) and hydrogen (2.1):
  • Chlorine pulls the shared electrons closer, creating a dipole.
• Key terms:
  • Permanent dipole: A charge difference that is always present.

Step 5: Explore Bond Types

• Bonds exist on a spectrum:
  • Ionic Bonding: High difference in electronegativity, one atom takes the electron from another.
  • Polar-Covalent Bonding: Small difference in electronegativity, unequal sharing of electrons.
  • Covalent Bonding: No difference in electronegativity, equal sharing of electrons.

Step 6: Differentiate Between Polar and Non-Polar Molecules

• Polar molecules have an overall dipole due to asymmetry:
  • Example: Water (H2O) is polar due to its bent shape.
• Non-polar molecules exhibit symmetry:
  • Example: Carbon dioxide (CO2) is non-polar despite having polar bonds because the dipoles cancel out.

Step 7: Practical Applications

• Understanding electronegativity and bond polarity helps predict molecular behavior in reactions, solubility, and interactions with other molecules.
• Use this knowledge in predicting the properties of substances, such as polarity and reactivity.

Conclusion

In this tutorial, you learned about electronegativity, how to measure it, the trends observed in the periodic table, and the implications of polar and non-polar bonds and molecules. Mastering these concepts is crucial for further studies in chemistry. As a next step, practice identifying electronegativity trends and predicting the polarity of various molecules based on their structures.