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Explore the history of the atom and the periodic table, including the contributions of Democritus, Aristotle, and John Dalton. Learn about the different parts of the atom and their significance. Discover the development of the periodic table by Mendeleev and Moseley. Understand the concept of isotopes and the practice of half-life. Identify the families and groups on the periodic table. Master electron energy levels and electron dot diagrams.
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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 ModelAssignment • Read p. 548 • Sketch the five types atomic models and label each with the yearand 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 • 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 • Bottom groups= Inner TransitionMetals • Group 13 = Boron Group • Group 14 = Carbon Group • Group 15 = Nitrogen Group • Group 16 = Oxygen Group • Group 17 = Halogens • Group 18 = Noble Gases Metalloids
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 e- level 2 = 8 e- level 3 = 18 e- level 4 = 32 e- p.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 xenonhave? • How many valence electrons does aluminum have?
