09 - Chapter 12 9/10/09 Dobereiner observed several groups...

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Chapter 12 9/10/09 Dobereiner observed several groups of three elements (triads) and noted that the atomic mass of 1 of the elements in the triad was the average of the other two: Cl, Br, I; S, Se, Te; Ca, Sr, Ba; Li, Na, K\ Newlands organized elements from lightest to heaviest in octaves compared them to music Introduced long periods, when an element didn’t fit in place he left a blank spot, & improved measures of atomic weights Still probs: atomic weights didn’t always give insight into placement in the table: Mendeleev ordered elements by reactivity and assigned numbers 1-92 1912 Mosley discovered that frequency of X-rays emitted from elements correlated with atomic number, not atomic weight (When atoms are bombarded with electrons, it is possible to eject electron from the inner shells; when an electron drops down from an outer shell, an X-ray is emitted) Mosley paved way for construction of mod periodic table based on atomic # # of protons in nucleus Rows are based on principle quantum number
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09 - Chapter 12 9/10/09 Dobereiner observed several groups...

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