Covalent bonds
Forming a covalent bond
A A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons. is formed when two The smallest part of an element that can exist. share a pair of Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. Covalent bonding occurs in most Element that is a poor conductor of electricity and heat, and which forms acidic oxides. A substance made of one type of atom only., and in A substance formed by the chemical union of two or more elements. formed between non-metals.
These shared electrons are found in the outer shells of the atoms. Usually each atom contributes one electron to the shared pair of electrons.
Learn more on covalent bonding in this podcast.
Listen to the full series on BBC Sounds.
The slideshow shows how a covalent bond forms between a hydrogen atom and a chlorine atom, making hydrogen chloride.
Image caption, 1. A hydrogen atom with one electron and a chlorine atom with 17 electrons
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Molecules
Most covalently bonded substances consist of small A collection of two or more atoms held together by chemical bonds.. A molecule is a group of two or more atoms joined together by covalent bonds. Molecules of the same element or compound always contain the same number of atoms of each element.
The atoms in a molecule are always joined together by a covalent bond. Substances that are made up of ions do not form molecules.
Sizes of atoms and simple molecules
A small molecule contains only a few atoms, so atoms and small molecules have a similar range of sizes. They are very small, typically around 0.1 nm or 1 × 10-10 m across.
Individual atoms and molecules are too small to see even with the most powerful light microscope. Some electron microscopes can produce images of atoms and simple molecules.
A water molecule, H2O, is about 0.3 nm (3 × 10-10 m) across:
Formulae of substances with simple molecules
The chemical formula of a substance with small molecules shows the number of atoms of each element in one molecule of the substance.
| Substance | Formula | Number of atoms |
| Hydrogen | H2 | Two hydrogen atoms |
| Oxygen | O2 | Two oxygen atoms |
| Nitrogen | N2 | Two nitrogen atoms |
| Hydrogen chloride | HCl | One hydrogen atom and one chlorine atom |
| Water | H2O | Two hydrogen atoms and one oxygen atom |
| Ammonia | NH3 | One nitrogen atom and three hydrogen atoms |
| Substance | Hydrogen |
|---|---|
| Formula | H2 |
| Number of atoms | Two hydrogen atoms |
| Substance | Oxygen |
|---|---|
| Formula | O2 |
| Number of atoms | Two oxygen atoms |
| Substance | Nitrogen |
|---|---|
| Formula | N2 |
| Number of atoms | Two nitrogen atoms |
| Substance | Hydrogen chloride |
|---|---|
| Formula | HCl |
| Number of atoms | One hydrogen atom and one chlorine atom |
| Substance | Water |
|---|---|
| Formula | H2O |
| Number of atoms | Two hydrogen atoms and one oxygen atom |
| Substance | Ammonia |
|---|---|
| Formula | NH3 |
| Number of atoms | One nitrogen atom and three hydrogen atoms |
Question
State the number of atoms of each type in one molecule of methane, CH4.
A methane molecule is made up of one atom of carbon and four atoms of hydrogen.
Question
State the number and type of atoms in one molecule of chlorine, Cl2.
A chlorine molecule is made up of two chlorine atoms.
An explanation of covalent bonding