itchyfruit
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Itroduction/pure element mass/size
Hi everyone,
I've been reading bits from this forum for a few weeks now(mainly in beginnings)and allthough i have and allways have had quite a passion for
chemistry i'm really not very good at it, i mention this because i hope this will explain why i ask what most of you would probably consider to be
stupid questions, so if you could just be patient with me at least till i catch up a bit/a lot!!
seemingly obvious question No1
I'm sure theirs a fairly simple formula to work this out (i even think we had it explained to us at school) but i can't remember it and allthough i've
looked i can't seem to find it. As an element collector i'm now at the point where most of the elements i need are getting expensive, so i would like
to be able to work out how many grams of a element i would need to get a reasonable size sample in cubic cm/cm3. I realise you probably can't be
bothered to explain this, but if you could just point me to a thread or site that does it would be a great help.
great site btw.
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itchyfruit
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opps
Sorry i forgot the n in introduction. Not a good start.
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Mr. Wizard
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You just need to look at the density of the element. This is the ratio of how much the element weighs compared to a one cubic centimeter water sample,
who density is 1 at a certain temperature. Thus if you had an element of density 6.2 you would need 6.2 grams of it to make a one cc sample.
Here is a wicki link to Sodium:
http://en.wikipedia.org/wiki/Sodium
A one cc sample would have a weight of 0.968 grams. This varies somewhat with temperature and allotrope of the element.
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itchyfruit
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Thanks Mr Wizard
That has certainly solved my how many grams of a element i need problem,just look it up on wikipedia, simples!!
Now for seemingly obvious question No2
Is their a way to calculate this from the information on the periodic table, if so does it have something to do with the carbon 12 scale (which i'm
currently trying to get my head round) if so i'm sure it will all become clear once i've learnt how to do the somewhat difficult (to me at least)
calculations. If not could i get another pointer?
Last silly question for today i promise  )
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Mr. Wizard
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I'm not sure exactly what you are asking. Are you asking if the size of a sample can be determined by the Atomic Number (AN), which is the number of
Protons inside a nucleus? The atomic number is how the atoms are roughly arranged in the periodic table. The number of Protons is exactly matched by
the number of Electrons circling the nucleus. The Protons exert influence on the Electrons and determine the chemical properties of the element. Thus
the AN determines the chemical properties.
Now for a complication. There are Neutrons also inside the nucleus. They weigh about the same as a Proton. They don't have a net charge, but they help
stabilize the nucleus and add weight to it. In fact almost all the weight or mass of an element is due to the combined weight of the Protons and
Neutrons in the element's nucleus. This is the Carbon 12 scale you were referring to. Normal Carbon has 6 Protons and 6 Neutrons giving it an Atomic
Weight (AW) of 12. Every element has an average AW. When you weigh out an element you have to keep the AW in mind.
A very smart Italian named Avagadro determined that it takes 6.023 x 10^23 atoms of a substance to equal it's Atomic Weight in grams. This number of
atoms is called a Mole. This lets you count atoms with a scale. This is quite a great tool for a chemist, and is a key concept for anybody doing any
chemistry.
http://en.wikipedia.org/wiki/Avagadro
Unfortunately the answer to your question about calculating the exact volume of a sample from its AN isn't easily done. If it is, maybe somebody else
can give you further guidance. In a general sort of way you can say that elements get more dense as they get bigger Atomic Numbers, but there are
exceptions.
[Edited on 15-6-2009 by Mr. Wizard]
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itchyfruit
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Thanks again
You did seem to get the question i was asking(despite the fact that i didn't really ask it that well) and your answer has certainly made things a
little clearer. I've just spent the last couple of hours looking up the volume of every single element on wikipedia and writing the weight in grams
per cm3 on my periodic table to see if any sort of pattern formed and to a certain extent their was, but as you said their are exceptions. So i've
concluded that it is indeed unlikely that the grams per cm3 can be worked out by a simple formula using the AN and would most likely have to be done
by displacement. I'm of to the science museum tomorrow to spend the day trying to get a better understanding of all this. Hopefully when i get back
i'll be a bit cleverer!!
thanks again for your explanation.
I don't know how that funny looking face appeared at the end of my last post it was supposed to be a smiley face!!
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entropy51
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For the periodic variation of atomic volume with atomic number see pages 77-78 and figure 4.8 of this book
http://books.google.com/books?id=ApD5nxhPzI4C&pg=PA77&am...
In their nomenclature density = RAM/atomic volume, where RAM is molar mass
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itchyfruit
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Thanks entropy51
I can see that this contains the sort of information i'm looking for, I don't actually fully understand it yet, but i'm going to keep reading it until
i do!!
Just incase anyone's interested i went to the science museum today and it was rubbish(from a chemistry point of view at least ) it didn't even have a
periodic table picture let alone samples and not a single model of a Atom in sight. useless
I think i'm going to have to get a scientific calculator and a book on scientific equations 
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The Fountain of Discordia
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Actually, in my (quite) limited experience, a pen and paper are quite sufficient for calculation purposes. I'm no genius in the maths either so.. Just
something to think about before spending money on a calculator.
Chemistry is art by other means.
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itchyfruit
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Your probably right but i need all the help i can get. I suppose a book that explains what all the little symbols and things like X over Y and to the
power of and so on and so forth would be more important, I still don't understand E=MC2 (i probably shouldn't mention that they'll probably chuck me
of the forum for not knowing that)
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entropy51
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I think the threshold for being chucked from the forum is rather higher than that!
Here is a link to an ancient but free book on chemical calculations that might get you started:
http://www.archive.org/details/chemicalcalculat017154mbp
If you google phrases such as "math for chemistry" more modern texts that you might want to eventually borrow or buy will come up.
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itchyfruit
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Thanks again for the handy link i will be studying it cover to cover
EEEEXCELLENT
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