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Mrs. Nielsen Chemistry
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The History of the Periodic Table By 1860, more than 60 elements had been discovered, but scientists had no way of organizing the elements. Dmitri Mendeleev’s first published periodic table A spiral periodic table
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Developed by Henry Moseley in 1911 Elements are organized by increasing atomic number Elements with similar properties occur at regular intervals
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Rows = “periods” Properties vary across a period Columns = “groups” or “families” Similar bonding capabilities Elements in a compound may be replaced by other elements in the same family.
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Families of Elements Group 2: Alkaline Earth metals Highly reactive Group 3-12: Transition metals Group 17: Halogens Very reactive, often react with alkali metals Group 18: Noble Gases Unreactive, already “happy” Group 1: Alkali Metals Highly reactive, not found as free elements in nature Why are Br and Hg a different color?
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Metals (“downstairs”) good conductors of heat and electricity malleable ductile tensile strength luster Non-Metals (“upstairs”) poor conductors of heat and electricity Metalloids (on the stairs) semi-conductors of heat and electricity
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Use the white boards with periodic tables to complete the following tasks. Put a star around the alkali metal that has 3 protons. Shade in the noble gas that is in the 4 th period. Circle the halogen that is a liquid at room temperature. Put a square around the transition metals. Label the Lanthanide series with an L. Label the Actinide series with an A. Draw a triangle around 2 of the metalloids. Put an “X” through the non–metal in Group 14. Draw a over the alkaline earth metal with an atomic # of 20.
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The Periodic Table as a REFERENCE TOOL
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29 Cu 63.55 Average Mass = a weighted average based on how common an isotope is. Element Symbol Atomic # = # of protons How do I use the periodic table as a reference tool?
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Examples: 1) You have 100 marbles. 25 marbles have a mass = 2.0g 75 marbles have a mass = 3.0g 2) There are 2 forms of naturally occurring copper. Copper – 63 (69.17%) = 62.929598 amu Copper – 65 (30.83%) = 64.927793 amu.6917 (62.929598) +.3083 (64.927793) = 63.55 amu.25 (2.0g) +.75 (3.0g) = 2.75 g
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The mass of an element can be used to determine either the atomic mass or the molar mass. Atomic Mass Molar Mass Units: Atomic mass unit (amu) = the mass of 1 atom of any element. One helium atom has a mass of 4.002 amu Units: grams per mole (g/mol) = the mass of 1 mole of atoms of any element. One mole of sulfur atoms has a mass of 32.066 g/mol
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What do these new units mean? Atomic Mass Units (amu) 1 amu = 1.660504 x 10 -24 g Carbon – 12 is set as the standard measurement at 12 amu. Therefore, the atomic mass of any element is found by comparing its mass with Carbon-12. Grams per Mole (g/mol) How many items are in 1 mole? Yes indeed! There are 6.02 x 10 23 items in 1 mole.
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The current world population is approximately 7 billion people. If everybody in the world was working together to count one mole of atoms, and each person is counting at a rate of 1 atom/second, it would take over 2.7 MILLION YEARS to count all of the atoms in one mole! Conclusion: 6.02 x 10 23 is a REALLY BIG number!
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