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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Page 1: 3-5 Organizing The Elements

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.

Page 2: 3-5 Organizing The Elements

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.

Page 3: 3-5 Organizing The Elements

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.

Page 4: 3-5 Organizing The Elements

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.

Page 5: 3-5 Organizing The Elements

John Newlands• 1st & 8th elements, 2nd & 9th

had similar properties, and so on.

• Law of octaves• Organized the first 14

“known” elements.– Pattern stopped

Page 6: 3-5 Organizing The Elements

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.

Page 7: 3-5 Organizing The Elements

Questions• What does periodic mean?

– Occurring at regular intervals.

Page 8: 3-5 Organizing The Elements

Mendeleev’s Predictions• He couldn’t complete his table because of

gaps in the elements.

• Those elements had not been discovered.

Page 9: 3-5 Organizing The Elements

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

Page 10: 3-5 Organizing The Elements

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.

Page 11: 3-5 Organizing The Elements
Page 12: 3-5 Organizing The Elements

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

Page 13: 3-5 Organizing The Elements

• http://education.jlab.org/elementflashcards

• http://www.webelements.com/

• http://pearl1.lanl.gov/periodic/