Grade 10 Chemistry Module 7: Electronegativity and Polarity

Grade 10 Chemistry Module 7: Covalent Bonding, Lesson 5: Electronegativity and Polarity

• Electronegativity: The tendency of an atom to attract bonding electrons towards itself. It influences bond type and polarity.

• Polar Covalent Bond: A covalent bond where electrons are not shared equally between atoms due to differences in electronegativity. One atom has a partial negative charge (δ⁻) and the other has a partial positive charge (δ⁺).

• Nonpolar Covalent Bond: A covalent bond where electrons are shared equally between atoms with identical electronegativities.

• Ionic Character: Covalent bonds can exhibit some ionic character, as the difference in electronegativity increases, the bond becomes more ionic.

• Electronegativity Trends: Electronegativity generally increases from left to right across a period and from bottom to top within a group on the periodic table. Fluorine (F) is the most electronegative element.

• Bond Length: The distance between the nuclei of two bonded atoms at the lowest potential energy.

• Bond Types:

  • Pure Covalent Bond: Atoms of identical electronegativities.
  • Polar Covalent Bond: Atoms of different electronegativities.
  • Ionic Bond: Atoms with a significant difference in electronegativity.

• Essentials Question:

  • How does electronegativity determine bond type?
  • How do polar and nonpolar covalent bonds compare?
  • What are the characteristics of covalently bonded compounds?

Starter Questions

• Group 1: Recall the definition of electronegativity and its position on the periodic table.

• Group 2: Analyze the relationship between electronegativity and ionic/covalent bond formation.

• Group 3: Critique how electronegativity values determine electron sharing in molecules.

Determining Bond Type

• Electronegativity Difference (ΔEN): The difference in electronegativity values between two bonded atoms.

• Bond Type Determination:

  • Zero ΔEN: Nonpolar covalent bond.
  • 0.4 - 1.7 ΔEN: Polar covalent bond.
  • ≥1.7 ΔEN: Ionic bond.

Polar and Nonpolar Covalent Bonds

• Symmetrical Shapes: Linear, trigonal planar, and tetrahedral molecular shapes can be nonpolar if the outer atoms are the same.

• Asymmetrical Shapes (Polar): Bent, trigonal pyramidal and other shapes are potentially polar; if the outer atoms are different, or there's a lone pair on the central atom.

Polar Molecules (criteria)

• Lone Pairs on Central Atom: Molecular shapes with lone pairs on the central atom tend to be polar.

• Unequal Outer Atoms: Molecules with different atoms surrounding the central atom (unequal electronegativity) might be polar.

• Solubility: Polar molecules usually dissolve in other polar substances ("like dissolves like").

Nonpolar Molecules

• Symmetrical Structure: Nonpolar molecules usually have symmetrical structures with identical surrounding atoms.

• Insolubility: Nonpolar substances generally dissolve in other nonpolar substances.

• Intermolecular Forces: Weak intermolecular forces like London Dispersion forces hold nonpolar covalent molecules together.

Intermolecular Forces

• Van der Waals Forces: Weak forces of attraction between molecules.
  • London Dispersion Forces: Weakest intermolecular force, temporary induced dipoles.
  • Dipole-Dipole Forces: Attraction between polar molecules.
  • Hydrogen Bonding: Strong dipole-dipole force, special case of attraction between a hydrogen atom bonded to N, O, or F and an electronegative atom on another molecule.

Properties of Covalent Compounds

• Low Melting/Boiling Points: Weak intermolecular forces lead to relatively low melting and boiling points.

• Soft Solids: Many covalent molecules are soft solids compared to ionic solids.

• Insoluble in Water (often): Nonpolar compounds do not dissolve readily in polar solvents like water.

• Solubility in Nonpolar Solvents (often): Often they do dissolve in similar substances – "like dissolves like".

Explore the concepts of electronegativity and polarity in covalent bonding through this quiz. Learn about polar and nonpolar covalent bonds, ionic character, and trends in electronegativity across the periodic table. Test your understanding of these key chemistry principles.