Understand Covalent Bonding

In this worksheet, students will learn about covalent bonding, and how to show it on a dot and cross diagram.

Key stage: KS 4

Year: GCSE

GCSE Subjects: Chemistry: Single Subject, Chemistry: Combined Science, Physical Sciences, Component 2: Concepts in Chemistry: Single Subject, Component 2: Concepts in Chemistry: Combined Science,

GCSE Boards: AQA, AQA Trilogy, AQA Synergy, OCR 21st Century, OCR Gateway, Pearson Edexcel, Eduqas,

Curriculum topic: Bonding, Structure and the Properties of Matter, Interactions Over Small and Large Distances, Chemicals of the Natural Environment, Elements, Compounds and Mixtures, Key Concepts in Chemistry, Bonding, Structure and Properties

Curriculum subtopic: Chemical Bonds: Ionic, Covalent and Metallic Structure and Bonding Why is Crude Oil Important as a Source of New Materials? Bonding Covalent Bonding Bonding, Structure and Properties

Difficulty level:

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Worksheet Overview

Ionic bonding works brilliantly when a compound has a metal and a non-metal in it. The metal atom loses unwanted electrons, the non-metal takes electrons it does want, and everything works well.

What if there isn't a metal and a non-metal? We need other types of bonding - covalent bonding happens between two non-metal atoms.

It's easy to mix up ionic and covalent bonding, so watch out for the ways in which they are similar and different.

A lot of very important substances are covalently bonded, so make sure you can remember the names and formulas of these ones:

Name	Formula
Water	H₂O
Ammonia	NH₃
Methane	CH₄
Carbon dioxide	CO₂

If both atoms are non-metals, there isn't a source of spare electrons to complete electron shells, so ionic bonding can't happen.

For example, imagine having two fluorine atoms. Each atom has seven out of eight positions filled in its outermost shell, and neither atom is going to give up any of its electrons. To solve this problem, the two atoms share one electron each.

The shared electrons sit in parts of the shell between the two atoms. A tiny fairy sitting in the middle of each atom would see a complete outer shell, but this only works if the two atoms are exactly the right distance between each other, making a bond between the atoms. This type of bond is called a covalent bond, and we can draw a dot-and-cross diagram for this sort of bonding as well. The covalent bond is the part where the circles touch or overlap.

Fluorine atoms form a covalent bond to make a fluorine molecule

In this diagram, only the outermost shells are shown, but it's usually easier to work out the dot and cross diagram by drawing all the shells.

You can do the same thing with compounds. Carbon dioxide is carbon and oxygen, and they are both non-metals. Carbon needs another four electrons, and oxygen needs another two. To make carbon dioxide, each bond between carbon and oxygen has two electrons from the carbon and two from the oxygen. If you look round each oxygen, they both seem to have eight electrons, and if you look round the carbon, it seems to have eight electrons.

Covalent bond between carbon and oxygen

Be really careful not to mix up the different dot-and-cross diagrams.

Remember:

If it's a metal with a non-metal, you have ionic bonding. One or more electrons move to the non-metal, but the atoms stay separate.

If it's a non-metal with a non-metal, you have covalent bonding. Some electrons are shared, so the atoms are drawn touching or overlapping.

Let's move on to some questions now.

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