What is a Covalent Bond?

Covalent Bond

A covalent bond forms when two atoms share one or more electron pairs, so each attains a stable electronic configuration.

Why Does Carbon Form Covalent Bonds?

IMAGE_SEARCH: 'electron dot structure of carbon atom diagram for education'

Electron-dot structure of a carbon atom

Valence Electrons & Octet Drive

Electronic configuration: \(1s^2\,2s^2\,2p^2\); carbon holds 4 valence electrons.

Octet rule states atoms seek 8 electrons in their outermost shell for stability.

Losing or gaining 4 electrons is energy-intensive, so carbon shares electrons, forming covalent bonds to complete its octet.

Key Points:

  • 4 valence electrons → half-filled outer shell
  • Octet rule drives atoms toward 8 valence electrons
  • Sharing electrons is the most energy-efficient path for carbon

Formation of Methane (CH₄)

1

Carbon wants an octet

Carbon has four valence electrons and needs four more to reach eight.

2

Hydrogen needs a duet

Each hydrogen atom has one electron and seeks one more to fill its shell.

3

Electron sharing

Carbon shares one electron with each hydrogen, forming four single covalent \( \text{C–H} \) bonds.

4

Methane structure

The tetrahedral molecule \( \text{CH}_{4} \) forms; carbon attains an octet and each hydrogen a duet.

Pro Tip:

A single covalent bond always represents one shared pair of electrons between two atoms.

Double Bonds: Ethene (C₂H₄)

IMAGE_SEARCH: 'ethene molecule dot cross diagram for education'

Double Covalent Bond in Ethene

Ethene (\(C_2H_4\)) is the simplest alkene.

Two carbons share two electron pairs, forming a double bond; each carbon also shares one pair with two hydrogens, completing the octet.

Key Points:

  • Double bond = 2 shared electron pairs between carbons.
  • Each carbon forms three σ bonds: 1 C = C and 2 C–H.
  • Octet rule satisfied: 8 shared electrons per carbon.
  • Double bonds are the defining feature of alkenes.

Single vs Triple Bonds

Methane (Single Bond)

Example: CH4
One shared electron pair forms each C–H σ bond
Longer and weaker bond length ≈ 109 pm

Ethyne (Triple Bond)

Example: C2H2
Three shared pairs: one σ + two π bonds
Shortest and strongest C–C bond ≈ 120 pm

Key Similarities

Both are covalent; electrons are shared, not transferred
Carbon atoms complete the octet in each molecule
Form stable hydrocarbons important in organic chemistry

Properties of Covalent Compounds

Low Melting / Boiling

Weak intermolecular forces make most covalent solids or liquids melt and vaporise at relatively low temperatures.

Poor Conductivity

Absence of free ions or electrons means covalent compounds do not conduct electricity or heat.

Solubility Pattern

They are generally insoluble in water but dissolve readily in non-polar organic solvents.

Multiple Choice Question

Question

Carbon mainly forms covalent bonds because it:

1
readily loses four valence electrons.
2
shares four electrons to achieve an octet.
3
gains four electrons from metals.
4
already has a complete outer shell.

Hint:

Think about how atoms satisfy the octet rule through electron sharing.

Key Takeaways

Lesson recap: covalent bonds form when atoms share electron pairs.

Carbon shares four valence electrons to complete its octet instead of losing or gaining them.

Single, double, and triple carbon bonds share one, two, or three pairs—bond strength rises as length falls.

Covalent compounds usually have low melting points, are poor conductors, and often exist as gases or liquids.

Thank You!

We hope you found this lesson informative and engaging.