2. Basic Chemistry Element: pure substance that cannot be chemically broken down into simpler kinds of matter. Atom: smallest unit of an element that retains all chemical properties of that element. Compound: a pure substance that is made of atoms from 2 or more elements that can exist in a free state. Molecule: the smallest unit of a compound that retains all chemical properties of that compound.

3. Atoms Contain a specific number of protons and neutrons within nucleus. Have the same number of electrons as protons in natural state. Therefore, they are electrically neutral. The atomic number = the number of protons. The atomic mass = the number of protons plus neutrons.

4. Isotopes and Ions Isotopes are atoms of the same element that have different numbers of neutrons. Therefore, their masses are unequal. Ions: atoms of the same element that have different numbers of electrons. Therefore, ions carry a charge. (atoms do not gain or lose protons under most natural conditions.)

5. Electron Configuration Electrons spin around the nucleus at different energy levels. The first energy level holds 2 electrons. The second and third hold 8. The number of electrons that an atom has determines its bonding ability. Draw configuration for, S, Br and F, Ca

6. Bonding Atoms with partially filled outer energy levels will bond with other atoms. Usually, if an atom lacks only one or two electrons OR has only one or two atoms in the outer level, it will form an ionic bond. If an atom needs OR can donate more than two electrons, it will form a covalent bond. Compare CH 4 and HCl.

7. Compounds and Formulas Compounds are made of molecules with several atoms. Molecules are represented by chemical formulas. The subscript means the number of atoms present in the molecule. A coefficient means the number of molecules that are present in a sample.

8. Examples of Compounds H 2 O has 2 hydrogen atoms and 1 oxygen HCl has 1 hydrogen atom and 1 chlorine C 6 H 12 O 6 has 6 carbon atoms, 12 hydrogen and 6 oxygen 2C 6 H 12 O 6 has 12 carbon, 24 hydrogen and 12 oxygen