Definition: Covalent Bond

Covalent Bond

A covalent bond forms when two atoms share electron pairs, allowing each to reach a stable outer shell.

Carbon's Valency: 4

Valency of Carbon

Carbon possesses 4 valence electrons. To satisfy the octet rule it must obtain 4 more, so it shares, rather than gains or loses, electrons—forming four covalent bonds.

Key Characteristics:

  • 4 valence electrons (2s² 2p²).
  • Needs 4 more to complete its octet (8 electrons).
  • Sharing electrons is energetically favoured over gaining or losing 4.

Example:

In methane (CH₄) carbon shares one electron with each hydrogen, achieving an octet.

Methane: A Simple Covalent Molecule

IMAGE_SEARCH: 'Lewis structure methane CH4 diagram electron dot for education'

Lewis structure of methane (CH₄)

Electron Sharing in CH₄

Carbon shares one electron with each hydrogen, creating four C–H single covalent bonds.

These shared pairs complete carbon’s octet and each hydrogen’s duet.

Key Points:

  • Lewis structure: central C surrounded by four H; each bond shown by a pair of dots or a dash.
  • Each C–H bond is a single covalent bond formed by one shared electron pair.
  • Structure satisfies the octet rule for carbon and the duet rule for hydrogen.

Step-by-Step: Forming Methane

1

List Electron Configurations

Write carbon \(2,4\) and hydrogen \(1\), showing four unpaired electrons on carbon.

2

Match Unpaired Electrons

Pair each carbon electron with one electron from a hydrogen—this is the electron pairing process.

3

Draw C–H Single Bonds

Show four shared pairs as four C–H covalent bonds—completing the bond formation sequence.

4

Confirm Stability

Carbon now has an octet, each hydrogen a duet; methane \( \mathrm{CH_4} \) is stably formed.

Pro Tip:

Sequential sharing of electrons is why covalent bonds form and why methane is tetrahedral.

Covalent vs. Ionic Bonds

Covalent Bond

Electrons are shared between atoms.
No ions; discrete molecules form.
Example: methane \(CH_4\).

Ionic Bond

Electrons are completely transferred.
Opposite ions attract in a crystal lattice.
Example: sodium chloride \(NaCl\).

Key Similarities

Both use valence electrons to reach noble-gas stability.
Both create stable chemical compounds.

Electron Dot Equation for Methane

\[\text{C}^{\bullet\bullet} + 4\,\text{H}^{\bullet} \;\longrightarrow\; \text{H{:}C{:}H}\]

Variable Definitions

C Carbon atom
H Hydrogen atom
• Non-bonding electron
: Shared electron pair (covalent bond)

Applications

Dot-and-Cross Representation

Shows four shared electron pairs, meeting the octet rule for carbon.

Stoichiometric Equation

Balanced form — C + 2H2 → CH4 — tracks atoms in the dot diagram.

Source: NCERT Grade 10

Multiple Choice Question

Question

Identify the compound that is primarily covalent.

1
NaCl
2
CaO
3
CH4
4
MgCl2

Hint:

Covalent bonds usually form between non-metal atoms.

Key Takeaways

Covalent bond: two atoms share electrons to achieve full outer shells.

Carbon owns four valence electrons; therefore, its valency is four.

Methane \(CH_4\): carbon shares one electron with each hydrogen, creating four covalent C–H bonds.

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Thank You!

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