1. PS-2.1 Compare the subatomic particles of an atom with regard to mass, location, and charge, and explain how these particles affect the properties of an atom (including identity, mass, volume, and reactivity).

2. The atom is composed of subatomic particles (protons, neutrons, and electrons) that affect the properties of an atom.

3. Protons and neutrons have about the same mass. One Atomic Mass Unit is equal to 1/12th the mass of one atom of Carbon-12. 1 Proton is approximately 1 a.m.u. 1 Neutron is approximately 1 a.m.u.

4. The mass of an electron is much less than the mass of protons and neutrons 1 Electron is approximately 0.0005 a.m.u.

5. Protons have a positive charge; know that neutrons have no charge. The net charge of the nucleus is positive and equal to the number of protons. Electrons have a negative charge. There is an attractive force between electrons and protons

6. There is a repulsive force between electrons and electrons, and between protons and protons Atoms are neutrally charged because the number of electrons is the same as the number of protons. Protons and neutrons are tightly bound in a tiny nucleus.

7. The nucleus is located in the center of an electron cloud.

8. The electron cloud is the space where electrons are moving erratically in areas of space called energy levels.

9. Energy levels are regions of space at increasing distances from the nucleus.

10. Home Work p. 549 #1-4