chemical periodicity. chemists used properties of elements to sort them into groups 1829, j.w....
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ChemicalPeriodicity
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• Chemists used properties of elements to sort them into groups
• 1829, J.W. Dobereiner’s classification system -elements in triads
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Dmitri Mendeleev• In 1869, Mendeleev’s table based on
increasing atomic mass.• Later same year, Lothar Meyer published a
very similar table• Elements with similar chemical properties are
in the same column.• Provided space for elements unknown at the
time.
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• In 1913, Henry Moseley identified an atomic number for each known element.•Modern periodic table
arranged by atomic number
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The Periodic Law• Elements in a group have similar properties• Properties of elements in a period change as
you move left to right• Pattern of properties in a period repeats as
you move from one period to the next• When elements are arranged in
order of increasing atomic number, there is a periodic repetition of their physical and chemical properties
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Three Classes of ElementsMetals, Nonmetals, Metalloids
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Alkali Metals• very reactive• good
conductors• end in s1
• need to lose 1e- to have noble gas configuration
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Alkaline Earth Metals
• end is s2
• Less reactive than alkali metals.
• need to lose 2e- to have noble gas configuration
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Halogens• combine easily
with alkali metals
• e- conf. ends in p5
• need to gain 1e- to achieve noble gas configuration
• “salt-formers”
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Noble Gases
• Full outer electron shell• Not likely to
form compounds
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Transition Metals
• Electrons are added to the d orbitals• Good
conductors of electricity• High luster
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Inner Transition Metals• Electrons are
added to the f orbitals• Rare Earth
elements
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Blocks on the Periodic Table
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