Atomicity
5 Minutes
Atomicity in chemistry for students: learn how atoms form molecules and how to calculate atomicity. A short science lesson in English.
- How chemical bonds join atoms to create molecules
- Homoatomic and heteroatomic molecules with examples
- Calculating atomicity for water, sugar, and coffee powder
What this lesson teaches
Atomicity is the total number of atoms present in a single molecule. While noble gas elements exist naturally as single unjoined atoms, atoms of other elements link together through chemical bonds to form molecules.
How atoms form molecules
There are 118 elements in the periodic table, and noble gases found in the final column exist on their own as single atoms. Except for these noble gases, atoms of elements join with two or more similar or different atoms to form molecules. The force that holds these atoms together is called an intramolecular force of attraction, also known as a chemical bond.
Types of molecules
- Homoatomic molecules are formed when atoms of the same element join together, including molecules like H2, O2, Cl2, and Br2.
- Heteroatomic molecules, which are also called compounds, are formed when atoms of different elements combine, such as sodium chloride, barium chloride, and water.
- Diatomic molecules contain two atoms, which can be homodiatomic when the atoms are identical or heterodiatomic when the atoms come from different elements.
- Triatomic molecules are made of three atoms, and molecules with even higher numbers of atoms are called polyatomic molecules.
Understanding atomicity
Atomicity refers to the total number of atoms present in a molecule. Because noble gases exist as single atoms, they are described as monoatomic and have an atomicity of one. When two atoms join, the molecule is diatomic and has an atomicity of two. Any molecule can have its atomicity calculated simply by counting all the atoms bonded within it.
Examples from the lesson
- A water molecule contains two hydrogen atoms and one oxygen atom, which gives it an atomicity of 3.
- Sugar has the formula C12H22O11, meaning all its carbon, hydrogen, and oxygen atoms add up to an atomicity of 45.
- The substance in coffee powder has the formula C8H10N4O2, giving it a combined atomicity of 24.
- Hydrogen chloride contains one hydrogen atom and one chlorine atom, making it a heterodiatomic molecule with an atomicity of 2.