Atomic structure

  • Thread starter Jadaav
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  • #1
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I got a question :

Why is the nucleon of Chlorine 35.5 ? Why is is not a whole number ?
 

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  • #2
Borek
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35.5 is not an atomic mass, it is atomic weight of the element.
 
  • #3
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What's the difference between atomic mass and atomic weight of an element ?
 
  • #4
Borek
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Have you ever heard about google and wikipedia?
 
  • #5
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Yeah, I searched in Wikipedia.
 
  • #6
Borek
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And you still don't know what is a difference between the two? Can you quote or write - in your own words - one line definitions of both?
 
  • #7
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Atomic mass is the mass of 1 atom comprising of its protons, neutrons and electrons.

Atomic weight is the average mass of all the atoms of an element that exist to 1/12 of the mass of an atom of Carbon - 12.

Am I right here ?

Wikipedia says this:

"The atomic mass is the total mass of protons, neutrons and electrons in a single atom (when the atom is motionless)"

Why does it specify when the atom is motionless ? Does it make a difference if its in motion ?

"Atomic weight (symbol: Ar) is a dimensionless physical quantity,..."

What is a dimensionless physical quantity ?
 
Last edited:
  • #8
Borek
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Am I right here ?
Yes.

Now, get back to your question and see if you can answer it.

Why does it specify when the atom is motionless ? Does it make a difference if its in motion?
Yes - moving objects get heavier (although for the effect to be observable their speed must be real high). Google for "relativistic mass".

What is a dimensionless physical quantity ?
One that has no units. Mass has units of kg (pound, stone...), length has units of m (feet, cable...), atomic weight has no units.
 
  • #9
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Now I got the answer to my question. It is not a whole number because it is the average mass of the element. When making averages, we often encounter decimals.
 
  • #10
Borek
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Wasn't that hard :smile:
 
  • #11
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Yeah, thanks to you:smile:
 

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