# periodic table question

Discussion in 'Earth Science' started by nlewis, Sep 16, 2002.

1. ### nlewisRegistered Member

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3
do you round the atomic weight of an element in the periodic table. For example oxygen has an atomic weight of 15.9994, do you round that to 16 especially if you are trying to find the amount of neutrons.

3. ### NenarTronianTeenaged TranshumanistRegistered Senior Member

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1,083
Yes. That 15.994 is an average number, dealing with isotopes (which you might not have learned ofyet) 15.994 is the average of Oxygen-16 and Oxygen-15, something like that. But when finding neutrons, round up, always.

5. ### James RJust this guy, you know?Staff Member

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30,812
The atomic weight is a weighted average of the atomic weights of the various isotopes of an element. Often, but not always, the most abundant isotope of an element will have a mass number which is the closest whole number to the atomic weight.

7. ### GiftedWorld WandererRegistered Senior Member

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2,113
It's also the weight in grams of a mole.