1. There are three states of matter: gas, solid and liquid All matter is made of atoms An element is made up of one type of atom A molecule is a combination of two or more atoms. (They can be the same element or different elements)

2. All atoms have a central part called a nucleus The nucleus is made up of two structures, protons that have a positive charge and neutrons which have no charge Orbiting around the nucleus are structures called electrons. They carry a negative charge. They are the smallest of the three structures Most atoms have the same number of electrons and protons

3. + Nucleus Electrons Neutron (neutral) Protons Atom

4. Periodic Table He Helium 2 4.0 Symbol Element Name Atomic Number Atomic Weight

5. Periodic Table The atomic number represents the number of electrons and protons He Helium 2 4.0 Symbol Element Name Atomic Number Atomic Weight The number of neutrons is calculated by subtracting the Atomic number from the Atomic Weight 4-2 = 2 neutrons in a Helium atom