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Physical Science Parts of the Atom & The Periodic Table History of the Atom Democritus – first person to think of what matter is made of around 400 BC. Theory was that matter was made up of substances. Aristotle – disputed Democritus and came up with his own theory that matter was uniform throughout and NOT made of smaller particles. Theory was accepted for 2000 years!!! UNTIL… John Dalton – proved that smaller “atoms” existed proving Democritus right and Aristotle wrong. Changes in the Atomic Model Assignment Read p. 548 Sketch the five types atomic models and label each with the year and the name and discoverer. Place these sketches on white paper and put in the basket. Parts of the Atom Protons (p+) Electrons (e-) Neutrons (no) History of the Periodic Table The periodic table was discovered by Dmitri Mendeleev in the late 1800s. He arranged the elements in order by their atomic masses. The first periodic table was written on paper!! p.554 In 1913, Henry Moseley rearranged the periodic table by their atomic numbers instead of the atomic masses. p.555 Periodic Table Atomic # = electrons and protons Mass # = protons plus neutrons (average atomic mass) Isotopes - atoms with the same number of protons but different number of neutrons Practice Sheet Half – Life 1. 2. Def: the time it takes for half of the radioactive atoms to change into another element due to a change in protons p. 552: Problem-Solving Activity Look at the table. How long does it take uranium-238 to turn to lead-206? How long would it take for 75% to change? Solutions: 1. 4,460 years 2. 3,345 years Families on the Periodic Table Group 1 = Alkali Metals Group 2 = Alkaline Earth Metals Group 3-12 = Transition Metals Metalloids Bottom groups= Inner Transition Metals Group 13 = Boron Group Group 14 = Carbon Group Group 15 = Nitrogen Group Group 16 = Oxygen Group Group 17 = Halogens Group 18 = Noble Gases Masses of Atoms mass of protons and neutrons are about the same mass of an electron is very, very close to zero (like a cloud) # of neutrons = mass # - atomic # average atomic mass – the weighted average mass of the mixture of isotopes (like grades done by %) Electron Energy Levels There are a possible 7 energy levels for the periodic table. There are enough known elements to occupy only 4 of these energy levels. level 1 = 2 elevel 2 = 8 elevel 3 = 18 elevel 4 = 32 ep.558-559 Electron Dot Diagrams Valence electrons – outer energy level electrons that can make chemical bonds Valence electrons are the ONLY electrons used in dot diagrams. Once dot diagrams are made, then electrons are paired to make compounds. Compounds are made by two ways: Covalent bonding = sharing e- OR Ionic bonding = transferring e- (taking them). Electron Dot Diagrams The Bohr model shows ALL electrons in their orbitals or paths The Lewis Dot Diagram shows just the valence electrons Valence Electrons Across PT Notice that the transition metals (3-12) are skipped!! Let’s Practice!! How many valence electrons does potassium have? How many valence electrons does bromine have? How many valence electrons does xenon have? How many valence electrons does aluminum have?