---
title: "Short note: chemical bond"
subject: "Civil Engineering Materials"
chapter: 1
key: "semester_3/civil_engineering_materials:chemical-bond"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/chemical-bond
site: BCT Engineering
---

# Short note: chemical bond

Civil Engineering Materials · Chapter 1: Introduction to Civil Engineering Material

- Asked in: 2070 Chaitra (old course), 4 marks
- Video: [Atomic Hook-Ups - Types of Chemical Bonds: Crash Course Chemistry #22](https://www.youtube.com/watch?v=QXT4OVM4vXI) — CrashCourse
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/chemical-bond
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-1

## Question

Write a short note on chemical bond.

## Short answer

Chemical bonds are forces holding atoms together. Primary bonds: ionic (electron transfer, hard/brittle), covalent (electron sharing, strong/directional), metallic (electron sea, ductile/conductive). Secondary van der Waals and hydrogen bonds are weak. Bond type determines properties like strength, conductivity, and melting point.

## Answer

A **chemical bond** is the force of attraction that holds atoms or ions together in a molecule or solid. Atoms bond to attain a stable (octet) electron configuration with lower energy. The type of bond decides the strength, melting point, ductility and conductivity of a material.

#### Primary (strong) bonds
1. **Ionic bond:** transfer of electrons from a metal to a non-metal, giving oppositely charged ions that attract each other (NaCl, MgO). Hard, brittle, high melting point, poor conductors in solid state.
2. **Covalent bond:** atoms share pairs of electrons (diamond, silica, polymers). Very hard and strong, directional, poor conductors.
3. **Metallic bond:** positive ions in a sea of free electrons (iron, copper). Ductile, malleable, good conductors.

#### Secondary (weak) bonds
- **Van der Waals and hydrogen bonds** between molecules. They are weak, found in polymers, bitumen, water and ice.

| Bond | Strength | Example material |
|---|---|---|
| Ionic | Strong | Ceramics, cement minerals |
| Covalent | Very strong | Silicates, diamond |
| Metallic | Moderate to strong | Steel, aluminium |
| Van der Waals | Weak | Plastics, bitumen |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. An ionic bond involves
   A. sharing of electron pairs
   B. a sea of electrons
   C. weak molecular attraction
   D. transfer of electrons from a metal to a non-metal
   Answer: D. NaCl, MgO. (Key point: Ionic)

2. A covalent bond involves
   A. sharing of electron pairs
   B. transfer of electrons
   C. free electron sea
   D. hydrogen attraction
   Answer: A. Diamond, silica. (Key point: Covalent)

3. Secondary bonds are
   A. the strongest
   B. weak, e.g. van der Waals and hydrogen bonds
   C. metallic
   D. ionic
   Answer: B. Found in polymers, bitumen. (Key point: Secondary)