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Atoms Atomic Structure and Models I. About Atoms A. B. C. Atoms are the building blocks of matter. Atoms are so small and numerous that we need to use indirect evidence to study them. The number of parts that each atom has determines its chemical properties. II. Dalton’s Atomic Theory 1. 2. 3. 4. 5. All matter is made of atoms. Atoms of the same element are the same. Atoms of different elements are different. Atoms combine to make molecules of compounds. Atoms cannot be created or destroyed (by physical or chemical processes). III. Parts of Atoms A. Protons 1. 2. 3. B. Located in the nucleus (central part of the atom) Have a mass of 1 atomic mass unit (amu) Have a positive charge Neutrons 1. 2. 3. Located in the nucleus Have a mass of 1 amu Have no charge (neutral) (Parts of atoms continued) C. Electrons Located outside of the nucleus Have a mass of 0 amu 1. 2. (actually 0.00055 amu but it’s so small that we ignore it) 3. Have a negative charge IV. Models of atoms A. Discoveries about atoms have changed how we picture atoms. V. Periodic Table & Atoms A. B. C. The Atomic number tells us how many protons are in an atom of a certain element. The Atomic number also tells us how many electrons are in a neutral atom. The Atomic mass is the total (on average) of the protons + the neutrons. “2 Rules to Remember” Atomic # = protons = electrons Atomic mass = protons + neutrons VI. Rule Breakers A. Ions 1. 2. 3. 4. 5. Ions have lost or gained electrons. They no longer have the same number of electrons as protons. Only the electron number can change (remember the electrons are on the outside) This means they have a net charge. Opposite charges attract, forming bonds between atoms. Rule Breakers (cont.) B. Isotopes 1. 2. 3. 4. Atoms of the same element can sometimes have extra or fewer neutrons than average. These different forms or weights of atoms are called isotopes. Isotopes that are heavier or lighter than “normal” can be radioactive. Radioactive atoms have nuclei that can change and give off energy in the process.