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Chapter 18 Atoms and the Periodic Table Section 1 (p. 544-549) Chemical Symbol: Shorthand way to write the name of the element. First letter capital letter Second letter lower case *Memorize Table 1, page 544 Atom: Smallest piece of matter that still has the properties of the element. Made up of Protons, Neutrons and Electrons Nucleus: Positively charged center of the atom. Contains 99.9% of the mass of the atom Size = 1/100,000 of the atom (like a golf ball in a football stadium) Protons Found in nucleus Positive 1 charge Mass = 1 a.m.u. Neutrons Found in nucleus Neutral (no charge) Mass = 1 a.m.u. Electrons: Found outside the nucleus Negative 1 charge Mass 1/1836 a.m.u. Quarks: Smaller particles that make up protons and neutrons Changing Atomic Model: See page 548 Democritus, 400 B.C.: Atoms make up all substances John Dalton, 1800’s: Proved that atoms exist Model of the atom went through many changes Electron Cloud Model: Current Model Electron Cloud Model: Electrons do not follow fixed orbits Electrons tend to occur more frequently in certain areas around the nucleus Electron Cloud: Area around the nucleus where atoms electrons are most likely to be found 100,000 x larger than the diameter of nucleus Contains different energy levels Ch. 18, Section 2 (p.550-553) Atomic Mass Unit (a.m.u.): The measurement used for atomic particles. Atomic Number: The number of protons in the nucleus of an atom. Specific for each element! Ex: Carbon atomic number 6 = 6 protons Ex: Oxygen atomic number 8 = 8 protons Ex: Sodium atomic number 11 = 11 protons Mass Number: Sum of the protons and neutrons in the nucleus of an atom. # neutrons = mass # - atomic # atomic number atomic mass Drawing Atoms 1. Begin by drawing the nucleus. Write in the number of protons and neutrons in the nucleus. 2. Place electrons in energy levels (remember number of electrons = number of protons in a neutral atom) 3. Fill in energy levels from inner levels to outer levels. 4. First energy level can hold up to 2 electrons. 5. Second and third energy levels can hold 8 electrons (for our class)