Atoms, elements and compounds
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Electricity
Waves
Forces and motion
Energy
Earth and atmosphere
Acids and alkalis
Chemical reactions
Pure and impure substances
The periodic table and properties of materials
Atoms, elements and compounds
States of matter
Genetics and evolution
Interactions and interdependencies
Plants
Human reproduction
Human gas exchange systems
Human nutrition, digestion and health
Human skeleton and muscles
Explainer Video
Summary
Atoms, elements and compounds
In a nutshell
Atoms are the small building blocks of life. Atoms of two or more elements chemically bond together to form compounds.
Atoms
Definition
Atoms are the small particles which make up everything in the universe.
Elements
Definition
An element is a substance made up of only one type of atom.
Example
Sodium is an element. The element sodium is made up of sodium atoms only.
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Compounds
Definition
Substances made up of more than one type of atom are called compounds.
Compounds form when atoms of different elements react. The atoms of the different elements are held together by chemical bonds.
There is a fixed ratio of different atoms throughout a compound.
Example
Water is a compound. All water molecules are made up of two hydrogen atoms chemically bound to one oxygen atom.
Mixtures
Definition
If a substance contains atoms of different elements, but the atoms are not bonded together then it is not a compound, it is referred to as a mixture.
Chemical symbols
To avoid writing out the full name of elements, atoms of each element can be referred to using a one or two letter symbols known as a chemical symbol.
Example
= carbon, = silver and = nitrogen.
Chemical formulas
Compounds can be represented by formulas. Formulas are made up of chemical symbols and they display the proportions of each element in a given compound.
Formulas can contain brackets. Everything inside the brackets is multiplied by the small number outside of the bracket.
Example 1
Water is made up of two hydrogen atoms and one oxygen atom. The formula for water is .
Example 2
The formula for acetic acid is . Each molecule contains two carbon atoms, four hydrogen atoms and two oxygen atoms.
Example 3
The formula for magnesium nitrate is . Each molecule contains one magnesium atom, two nitrogen atoms and six oxygen atoms.
FAQs - Frequently Asked Questions
How do you calculate the number of neutrons an atom has?
To work out the number of neutrons an atom has, subtract the atomic number from the mass number.
What are chemical formulas?
Chemical formulas are made up of chemical symbols and display the proportions of each element in a given compound.
What are atoms?
Atoms are particles which everything is made up of.