2. Aim: What is matter? I. Matter – anything that has mass and volume. A. Atoms - A unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. 1. Nucleus – contains protons (+ charge) and neutrons (neutral or no charge). 2. Electron cloud – contains electrons (- charge) that move (orbit) rapidly around the nucleus.

4. B. Element - A substance composed of atoms having an identical number of protons in each nucleus. Elements cannot be reduced to simpler substances by normal chemical means.

5. 1. Elements are classified according to the number of protons (atomic number) in the nuclei of the atoms. a. Hydrogen has only 1 proton. Oxygen has 8 protons. Carbon has 6 protons.

6. Understanding the Periodic Table Atomic Number: The number of protons in the nucleus of the atom Name of element Element Symbol: One or two letters, 1 st letter always capitalized, 2 nd always lower case Atomic Mass: Sum of protons and neutrons in the nucleus