3-5 organizing the elements
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Warm – Up• Is flammability a physical or chemical
property? Why?– Chemical property because burning a
substance is combining with oxygen and creating a new substance
• What happens to the composition of matter during a physical change?– The substance does not change only shape
or some other physical change takes place.
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3-5 Organizing Elements• Objectives
– Describe how Medeleev arranged the elements in his table.
– Explain how the predictions helped verify the usefulness of his periodic table.
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Why do we classify/organize?• How are most library books classified?
• Why is this classification useful?
• How do Biologist classify living organisms?– Domain, Kingdom, Phylum, Class, Order,
Genus, Species.
• Why do we classify/organize?– Easier to find and identify.
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Searching For Order• Until 1750, only 17 elements were known.• Most identified were metals.• In 1789, Lavoisier grouped atoms into 4
types.– Metals, nonmetals, gases and earths.
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John Newlands• 1st & 8th elements, 2nd & 9th
had similar properties, and so on.
• Law of octaves• Organized the first 14
“known” elements.– Pattern stopped
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Mendeleev’s Periodic Table• In 1860, he used solitaire to help him
organize the known 63 elements– Wrote element on a card– Looked at the elements properties.– Lined the cards up in increasing mass.– He saw a pattern that repeated.– Rearranged to create columns of similar
properties.
• Properties repeat from row to row.
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Questions• What does periodic mean?
– Occurring at regular intervals.
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Mendeleev’s Predictions• He couldn’t complete his table because of
gaps in the elements.
• Those elements had not been discovered.
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Other Systems• In 1829, Dobereiner proposed a law of
triads.– It is a group of 3 similar elements.– The middle element has properties between
the other two.– Example
• Li – 6.941• Na – 22.990• K – 39.098• Average (6.941+39.098)/2 = 23.02
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Evidence for Mendeleev’s Table• He named missing elements after the same
group.• I.E. Element below Al, he named eka-
aluminum.• He predicted it would be a soft metal with
low melting point and a density of 5.9 g/cm3.• French chemists actually discovered it in
1875. • Gallium (Ga) is a soft metal with 29.7oC
M.P. and a density of 5.91 g/cm3.
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Questions• How was Mendeleev’s table organized?
– Elements are arranged in order of increasing mass.
• How do the properties repeat?– Row to row.– New columns are created for each set of
similar properties
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• http://education.jlab.org/elementflashcards
• http://www.webelements.com/
• http://pearl1.lanl.gov/periodic/