Chemical Bonding: Ionic, Covalent and Coordinate Bonds Explained

Why does common salt dissolve in water while diamond does not? Why is oxygen a gas but iron a solid? The answers lie in chemical bonding — the way atoms join together to form molecules and crystals. This chapter is one of the highest-weightage topics in CBSE, ICSE and Federal Board chemistry exams.

STEMBridge Learning thumbnail on chemical bonding, showing ionic, covalent, and coordinate bonds, Lewis structures, and molecular shapes in a clean educational layout without any person.

Why Do Atoms Form Bonds?

Atoms bond to achieve a stable electronic configuration, usually that of the nearest noble gas. This is known as the octet rule — atoms tend to gain, lose, or share electrons to complete eight electrons in their outermost shell (or two for hydrogen and helium).

Types of Chemical Bonds

1. Ionic (Electrovalent) Bond

Formed by the complete transfer of electrons from a metal to a non-metal. The resulting positive and negative ions are held together by strong electrostatic attraction.

Example: Na (loses 1 electron) + Cl (gains 1 electron) → Na⁺Cl⁻

Properties of ionic compounds:

High melting and boiling points.
Soluble in water; insoluble in non-polar solvents.
Conduct electricity when molten or dissolved in water.
Form crystalline solids.

2. Covalent Bond

Formed when two non-metal atoms share one or more pairs of electrons.

Single bond: One shared pair (H–H).
Double bond: Two shared pairs (O=O).
Triple bond: Three shared pairs (N≡N).

Properties of covalent compounds:

Low melting and boiling points.
Mostly insoluble in water; soluble in organic solvents.
Do not conduct electricity in pure form.
Exist as gases, liquids, or soft solids.

3. Coordinate (Dative) Bond

A special type of covalent bond in which both electrons of the shared pair come from one atom only. Common examples include NH₄⁺ and H₃O⁺.

Lewis Dot Structures

Lewis structures show valence electrons as dots around the element symbol. They help us visualise how atoms share or transfer electrons during bond formation.

Example

The Lewis structure of water shows oxygen sharing one electron pair with each of two hydrogen atoms, leaving two lone pairs on oxygen.

Polar and Non-polar Covalent Bonds

Non-polar covalent bond: Electrons are shared equally between identical atoms (e.g., H–H, O=O).
Polar covalent bond: Electrons are shared unequally due to a difference in electronegativity (e.g., H–Cl, H–O).

Bond polarity is determined by electronegativity difference:

0.0 – 0.4: Non-polar covalent
0.4 – 1.7: Polar covalent
Greater than 1.7: Ionic

Hydrogen Bonding

A special attractive force between a hydrogen atom bonded to a highly electronegative atom (N, O, F) and another electronegative atom. Hydrogen bonds explain why water has unusually high boiling and melting points and why ice floats.

VSEPR Theory and Molecular Shapes

The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shapes based on the repulsion between electron pairs around a central atom.

CH₄ → tetrahedral (109.5°)
NH₃ → pyramidal (107°)
H₂O → bent (104.5°)
CO₂ → linear (180°)

Metallic Bonding

In metals, the outer electrons are loosely held and form a "sea of electrons" surrounding the positively charged metal ions. This explains why metals conduct electricity, are malleable, and shine.

Common Mistakes Students Make

Drawing dot structures without checking octet completion.
Confusing ionic and covalent properties in MCQs.
Forgetting that hydrogen forms only a single bond, never double or triple.

Frequently Asked Questions

Q1. Why are ionic compounds solid at room temperature?
Because the strong electrostatic forces between oppositely charged ions hold them in a rigid crystal lattice.

Q2. Why do covalent compounds not conduct electricity?
Because they have no free ions or electrons to carry charge.

Q3. Is HCl ionic or covalent?
HCl is a polar covalent molecule, but in water it ionises completely to form H⁺ and Cl⁻.

Q4. What makes hydrogen bonding so important in biology?
It holds together the two strands of DNA and gives proteins their folded shapes.

Q5. Can the octet rule be broken?
Yes. Boron (BF₃) has only 6 electrons, while sulphur in SF₆ has 12 — these are called exceptions to the octet rule.

Key Takeaways

Atoms bond to attain stability. Metals transfer electrons to non-metals to form ionic bonds, while non-metals share electrons to form covalent bonds. Coordinate, metallic, and hydrogen bonding round out the picture. Understanding bonding is the gateway to understanding chemical reactions, structures, and the physical properties of every substance around you.