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“periodic”= regular, repeated pattern
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Dmitri Mendeleev Russian Chemist Studied phys. Properties of elements
Created PT in 1869 Arranged in order of increasing atomic mass Predicted undiscovered elements
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Mendeleev’s PT published 1869
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Henry Moseley English physicist who studied under Rutherford
Improved PT by arranging in order of increasing atomic #
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PERIODS Rows across the PT Atomic # increases from left to right Physical & Chemical properties change in predictable patterns Numbered 1 to 7 down side
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Period # = number of energy levels/electron shells
Lithium Period 2 Sulfur Period 3
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Groups/ Families Elements in same column (up & down)
Numbered 1-18 across top of PT Share similar physical & chemical properties
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Group # = # of valence electrons
Magnesium Group 2 = 2 valence e- Neon Group 18 = 8 valence e-
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