# Atoms Revision

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1. What is an atom?
An atom is the smallest piece of a substance that is that is still a substance.
2. What are atoms made up of?
• Even smaller particles called subatomic particles.
3. What are atoms made up of?
Protons (P+) Neutrons (N) Electron (E-)
4. Protons (P+)
• Protons have a positive charge. (+)
• They sit at the very center of an atom in a heavy core called the nucleus.
5. Neutrons (N)
• Neutrons have no charge. So they are neutral (N).
• Neutrons are the heaviedt of all sub-atomic particles, being just a little heavier then a proton. Neutrons sit in the nucleus with the Protons.
6. Eletrons (E-)
• Electrons have a negaative charge (-).
• They are very light. They are only 1/2000th the mas of a proton.
• Eletrons spin around the nucleus at very high speeds.
• The region in which electrons spin is huge compared to the size of the nucleus.
• There are only electrons in this regions. These region are known as electron shells or energy levels.
7. All atoms are electrically neutral (they have no charge). This means the charge of every proton must be cancelled out by the charge of an eletron.
• Number of Protons
• =
• Number of Electrons
8. The number of protons in an atom is called its an atomic number. The atomic number gives an atom it's place in the periodic table. But because there are the same number of eletrons as there are protons you can find out the atomic number by finding ou the number of eletrons.
• Atomic Number
• = Number of protons
• =Number of electrons
• = Place in periodic table
9. Mass Number
The mass number of an atom is the total number of particles in its nucleus.
• Mass Number
• = Number of protons + Number of neutrons
10. Find out how many protons electrons and neutrons there are in an atom
• Protons = Atomic number
• Neutrons = Mass number - Atomic Number
• Electrons = Protons = Atomic number
11. Scientists short hand way of writing this information looks like this