1. HELIUM ATOM + N N + - - proton electron neutron Shell

2. ATOMIC STRUCTURE Particle proton neutron electron Charge + charge - charge No charge 1 1 none Mass

3. ATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom He 2 4 Atomic mass Atomic number number of electrons = number of protons in a neutral atom

4. ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. 1 st shella maximum of 2 electrons 2 nd shella maximum of 8 electrons 3 rd shella maximum of 8 electrons 4 th shella maximum of 18 electrons

5. SUMMARY 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Mass Number of an atom = number of Protons + Neutrons in the nucleus. 3. We find the Mass Number by rounding the atomic mass to the nearest whole number 3. The number of Protons = Number of Electrons 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons.