Covalent Bond

A covalent bond forms when nonmetal atoms share electron pairs. As the atoms approach, energy falls to a minimum at the bond length; too close, and repulsion rises again. Higher bond order means greater bond energy and shorter length, and electronegativity difference decides polar versus nonpolar. Here you change bond length and bond order to compare the energy curve and single, double, and triple bonds.

How Does a Covalent Bond Form?

Bond length3

💡 Analogy: Holding a Ball Together

①Two children sharing a ball (electron pair)

②Closer → lower energy (stable) — but too close repels

③Optimal distance = bond length (energy minimum)

④Unlike ionic, electrons are 'shared'

Single / Double / Triple Bonds

Bond order1

Bond Order and Properties

Bond order ↑ → bond energy ↑, bond length ↓

Triple > double > single (in strength)

🔍 Compare the Three Bond Types!

①Single: 1 σ bond (H₂, Cl₂)

②Double: σ + π (O₂, C=C)

③Triple: σ + 2π (N₂, C≡C)

④Higher order = shorter and stronger

Electronegativity and Polarity

Polar Covalent Bond

ΔEN > 0 → electron pair shifts to one side

ΔEN: difference in electronegativity

Nonpolar Covalent Bond

ΔEN = 0 → electrons shared equally

Same element bonded (H₂, O₂, N₂)

💡 A Continuous Spectrum of Bonds

①ΔEN = 0: nonpolar covalent (H-H)

②0 < ΔEN < 1.7: polar covalent (H-Cl)

③ΔEN > 1.7: ionic (Na-Cl)

④Bonds form a continuous spectrum, not a binary

Work It Out

Example 1

How do the two hydrogen atoms bond in a hydrogen molecule (H₂)? How many shared electron pairs are there?

Each H contributes one electron, so they share one electron pair (a single bond).

H· + ·H → H:H (H−H)

Count the shared electron pairs.

1 shared electron pair (single bond)

▸ single bond, 1 shared electron pair

By sharing one electron pair, each atom reaches a stable helium-like configuration.

Example 2

Find the bond type and the numbers of shared and lone (unshared) electron pairs in a nitrogen molecule (N₂).

Each N has 5 valence electrons and shares 3 of them, forming a triple bond.

N≡N (triple bond)

Count the shared pairs and the remaining lone pairs.

3 shared pairs, 2 lone pairs

▸ triple bond (3 shared, 2 lone pairs)

Each N keeps one lone pair (two total), and the triple bond makes N₂ very strong and short.

Summary

Covalent Bond

non-metal + non-metal → electron pair sharing

Forms between elements with small electronegativity difference

2023 KICE mock Chemistry I type, adapted

Which of the following molecules contains a double bond?

①H₂

②Cl₂

③O₂

④N₂

⑤HCl

▸ ③ O₂

Compare the bond order of each molecule (H₂·Cl₂·HCl single, N₂ triple).

Check the bond order of the remaining O₂.

O₂: O=O double bond (2 shared electron pairs)

🎯 Exam Points

①Covalent = non-metal + non-metal (sharing)

②Higher bond order → larger energy, shorter length

③σ = head-on overlap, π = side overlap

④Polar: ΔEN > 0; nonpolar: ΔEN = 0

⑤Coordinate bond: one atom donates both electrons (NH₄⁺)

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Ionic Bond

Molecular Structure

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