Meet Covalent Bonds

Two hydrogen atoms sharing electrons

Two hydrogen atoms share one electron pair to form H₂.

Atoms share electrons to stay stable

A covalent bond forms when two atoms share one or more pairs of electrons.

Example: In hydrogen gas (H₂) each H atom shares its single electron, so both feel a full first shell.

Key Points:

  • Covalent bond = shared electron pair.
  • Hydrogen + Hydrogen → H₂ by sharing one pair.
  • Sharing keeps both atoms electrically neutral.

Carbon’s Four Hands

Methane model showing four C–H bonds

Model of methane \(CH_4\)

Carbon Valency = 4

Carbon has four valence electrons, giving it a valency of 4.

By sharing each electron with a hydrogen atom, carbon forms methane, \(CH_4\).

Key Points:

  • Carbon’s valency is 4.
  • Methane \(CH_4\) proves this: carbon bonds with 4 hydrogens.

Single, Double, Triple

Bond multiplicity counts shared pairs. Goal: spot the difference between single, double and triple covalent bonds.

1

Single Bond

Atoms share one electron pair. Longest and weakest covalent bond.

2

Double Bond

Atoms share two pairs. Stronger and shorter than a single bond.

3

Triple Bond

Atoms share three pairs. Shortest and strongest covalent bond.

Pro Tip:

More shared pairs = stronger and shorter bond.

Diamond – A Hard Giant

https://cdn.mathpix.com/cropped/2025_06_26_a5c8b508ed279c540c23g-04.jpg?height=350&width=475&top_left_y=996&top_left_x=319

Tetrahedral network of carbon atoms

Diamond is an allotrope of carbon built from a continuous tetrahedral network.

Each carbon atom shares electrons with four others, forming strong covalent bonds in 3-D.

Key Points:

  • Pure carbon allotrope made only of C–C bonds.
  • 4 bonds per atom give a rigid tetrahedral lattice.
  • Endless 3-D lattice makes diamond the hardest natural material.

Graphite – Layers that Slide

https://cdn.mathpix.com/cropped/2025_06_26_a5c8b508ed279c540c23g-04.jpg?height=339&width=336&top_left_y=1004&top_left_x=819

Layered Structure & Properties

Graphite is an allotrope of carbon built from flat, hexagonal sheets stacked one above another.

Weak forces between the layered sheets let them slide easily, so graphite feels soft and writes smoothly.

Each carbon contributes one delocalised electron that moves within a sheet, giving the material good electrical conductivity.

Key Points:

  • Allotrope: Graphite has layered sheets of carbon atoms.
  • Layer sliding → softness; free electrons within a sheet → conductivity.

Diamond vs Graphite

Diamond

Hardest natural substance; resists scratching.
Electrical insulator; no free electrons.
Transparent, brilliant crystal lattice.

Graphite

Soft, layers slide easily; marks paper.
Good electrical conductor; delocalised electrons.
Black and shiny, layered structure.

Key Similarities

Both are pure carbon allotropes.
Strong covalent bonds give high melting points.

Saturated Chains

https://cdn.mathpix.com/cropped/2025_06_26_a5c8b508ed279c540c23g-06.jpg?height=414&width=608&top_left_y=1049&top_left_x=1234

Ball-and-stick model of ethane

Ethane: a Saturated Hydrocarbon

Ethane (C₂H₆) shows what “saturated” means.

Its two carbons share one single C–C bond; each carbon is filled by hydrogen.

Quiz: Propane has ___ carbon–carbon double bonds.

Key Points:

  • Only single bonds between carbon atoms.
  • Follow general formula \(C_nH_{2n+2}\).

Homologous Series

Homologous Series

A group of organic compounds with the same general formula. Each successive member differs by exactly one \(–\mathrm{CH_{2}}\) unit. This constant gap causes gradual changes in physical properties.

{% if context %}

{{ context }}

{% endif %}
{% if source %}

Source: {{ source }}

{% endif %}

Isomers of Butane

Straight-chain and branched isomers of butane

Straight-chain (n-butane) vs branched (iso-butane)

One formula, two shapes

Butane \( \mathrm{C_4H_{10}} \) exhibits structural isomerism.

It exists as a straight chain and a branched ‘T’, sharing the same formula but different atom arrangement.

Key Points:

  • Straight chain: CH3-CH2-CH2-CH3
  • Branched chain: (CH3)3-CH
  • Different shapes ⇒ different physical properties; branched boils lower.
  • Demonstrates how one formula can give multiple structures.

Name That Formula!

Practice your formula recognition: drag each alkane name onto its correct molecular formula.

Draggable Items

Methane
Ethane
Propane
Butane

Drop Zones

CH₄

C₂H₆

C₃H₈

C₄H₁₀

Tip:

Remember: the number of hydrogens is twice the carbons plus 2 for alkanes.

Key Takeaways

Recap: Carbon forms covalent bonds by sharing electrons.

It can make single, double, and triple bonds.

Catenation lets carbon build long chains and rings.

Different atom arrangements cause isomerism.

Network structures create diamond, graphite, and other allotropes.

Thank You!

We hope you can now recall the main points of carbon chemistry.