Covalent Bonding - The Basics and Bond Polarity

Covalent Bonding - The Basics and Bond Polarity

Introduction

  • Essential Question: What determines the covalent nature and properties of a substance?

Covalent Bonds

  • Definition: A covalent bond is the simultaneous electrostatic attraction between a pair of electrons and positively charged nuclei.

  • General Characteristics:

    • Typically form between two non-metals.

    • Electron pairs are shared to achieve a stable electron configuration known as the octet rule.

Types of Covalent Bonds

Single Covalent Bond

  • Example: Formation of the F-F bond in fluorine gas (F₂).

    • Involves the sharing of 1 pair of electrons.

Double Covalent Bond

  • Example: Formation of the O-O bond in oxygen gas (O₂).

    • Involves the sharing of 2 pairs of electrons.

Triple Covalent Bond

  • Example: Formation of the N-N bond in nitrogen gas (N₂).

    • Involves the sharing of 3 pairs of electrons.

Comparing Single, Double, and Triple Covalent Bonds

  • Data Comparison:

    • Bond Enthalpy Definition: The energy required to break one mole of a given type of bond, where stronger bonds require more energy to break.

Bond Type

Bond Length (nm)

Bond Enthalpy (kJ mol⁻¹)

Observations

Single

0.154

347

Bond strength increases with the number of shared electron pairs. Bond length decreases as bond strength increases.

Double

0.134

612

Bond strength increases with the number of shared electron pairs. Bond length decreases as bond strength increases.

Triple

0.120

838

Bond strength increases with the number of shared electron pairs. Bond length decreases as bond strength increases

Types of Covalent Bonds and Electronegativity

Definitions and Concepts

  • Electronegativity (EN): A property of an atom indicating its ability to attract electrons.

  • Measurement: Using the Pauling Scale, where values range from 0 to 4:

    • 0: No or little tendency to attract electrons

    • 4: Strong tendency to attract electrons

  • EN Definition: Defined as the measure of the tendency of an atom to attract a shared pair of electrons to itself.

  • Data Reference: Electronegativity values can be found in Table 9 of the Data Booklet.

Electronegativity Trends

  • General Trends:

    • Metals have lower electronegativity values; Non-metals have higher values.

    • Group 18: Noble gases exhibit no electronegativity.

  • Electronegativity Values: Examples include:

    • Fluorine (F): EN = 4.0

    • Bromine (Br): EN = 3.0

    • Lithium (Li): EN = 1.0

    • Potassium (K): EN = 0.8

Nature of Sharing in Covalent Bonds

Non-Polar Covalent Bonds

  • Characteristics:

    • Involve equal sharing of electrons between atoms of the same element.

    • Such atoms possess equal electronegativity (EN).

Polar Covalent Bonds

  • Characteristics:

    • Involve unequal sharing of electrons, resulting in the formation of dipoles (regions of partial charge).

    • Example: Hydrogen (H) with EN = 2.2 and Bromine (Br) with EN = 3.0.

    • The electron cloud shifts closer to the atom with the higher electronegativity, creating a dipole:

      • δ+ (partial positive) on H

      • δ– (partial negative) on Br.

    • Bond Dipole Representation:

    • Indicated by an arrow pointing toward the more electronegative atom.

Strength of Polar Covalent Bonds

  • Relation to Electronegativity Difference (ΔEN):

    • The strength of a bond is influenced by the ΔEN between the bonded atoms.

    • Sample ΔEN values:

    • Least polar bond: ΔEN = 0.4

    • Moderate polar bond: ΔEN = 0.9

    • Most polar bond: ΔEN = 1.9

    • Symbol Representation: The length of the symbol denotes the strength of the bond dipole.

The Bonding Continuum

  • Concept: Describes the spectrum of bond types based on ΔEN values ranging from non-polar to ionic.

  • Data Reference:

    • Non-polar covalent: ΔEN = 0.0

    • Polar covalent range: 0.0 < ΔEN < 1.7

    • Ionics: ΔEN ≥ 1.7

  • Covalent and Ionic Character %:

    • Increases in bond polarities from non-polar (100% covalent, 0% ionic) to ionic bonds (0% covalent, 100% ionic).

Application of The Bonding Continuum

  • Predict Bond Type: Using electronegativity values, students can predict the type of bond in the following pairs:

    • Mg + O

    • H + Cl

    • C + S

    • Cu + S

    • I + Br

    • N + N

  • Molecular Examples: For examination of bond type in given molecules:

    • CO₂

    • PCl₃

Bonding in Period 3 Oxides

  • Molecular Formulas and Bond Types:

    • Na₂O: ionic

    • MgO: ionic

    • Al₂O₃: giant covalent

    • SiO₂: giant covalent

    • P₄O₁₀: molecular covalent

    • P₄O₆: molecular covalent

    • SO₃: molecular covalent

    • SO₂: molecular covalent

    • Cl₂O₇: molecular covalent

    • Cl₂O: molecular covalent

Bonding in Period 3 Chlorides

  • Molecular Formulas and Bond Types:

    • NaCl: ionic

    • MgCl₂: ionic

    • AlCl₃: molecular covalent

    • SiCl₄: molecular covalent

    • PCl₅: molecular covalent

    • PCl₃: molecular covalent

    • S₂Cl₂: molecular covalent

    • Cl₂: molecular covalent