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Hope you had a great weekend! Test on Friday – Start studying a little each night. Isotopes are atoms of the same element with different numbers of _________ which results in different _______ numbers. What are three isotopes of Hydrogen? When you’re done with the warm-up, look over the element math worksheet from last Thursday because we’re going to start class with a quiz.

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Chemistry!! Unit Two, Day Three Kimrey 10 September 2012

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Suppose that there were two isotopes of Sodium. 28% of the naturally occurring sodium atoms had a mass of 22, and 72% atoms had a mass of 23. What would the average atomic weight of sodium be?

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28% =.28 72% =.72 (.28 x 22 ) + (.72 x 23 ) = 22.72 amu

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Suppose that there were two natural isotopes of Copper. 80% of the atoms had a mass of 63, and 20% of the atoms had a mass of 65. What would the average atomic weight of copper be?

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80% =.80 20% =.20 (.80 x 63) + (.20 x 65) = 63.4 amu

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Suppose that a new element (E) were discovered that existed as three natural isotopes. 25% of the atoms had a mass of 278, 38% had a mass of 281, and the remainder had a mass of 285. What would be listed as the atomic weight of this element?

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25% =.25 38% =.38 100% - (25% + 38%) 37% =.37 (.25 x 278) + (.38 x 281) + (.37 x 285) = 281.73 amu

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