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rjb93 rjb93
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Posts: 11
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11 years ago
I have been given a question for my level 3 pharmacy test giving me the atomic mass of an atom and the number of neutrons, and asking how many electrons this atom has. I have searched high and low for a way of calculating this but everything I come across says you need an atomic number to work it out, which I don't. There must be a way as when I selected answer 'It's impossible to tell', it came back from the examiner as incorrect.
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wrote...
11 years ago
atomice mass = no of protons + no. of neutrons in an atom
if u subtract atomic mass and no. of neutrons like this:-
atomic mass - no. of neutrons = no. of protons

now as u know the no. of protons and electrons in an atom are SAME
so if u know the no. of protons , then u will automatically knw the number of electrons Slight Smile
wrote...
11 years ago
You can figure out the atomic number from the information given.

Most of an atom's mass is in the nucleus.  Electrons don't have much mass.  Multiply mass of a neutron by # of neutrons in atom.  Subtract from atomic mass.  You get mass of protons in the atom.  Divide by mass of a proton.  You should get something very close to a whole number.  This is the number of protons in the atom and thus your atomic number.

P.S.  There seem to be some people who do not like my instructions for working out the atomic number.  If there is an error, please let me know.
wrote...
11 years ago
atomic mass = number of protons + number of neutrons
thus
number of protons = atomic number =  atomic mass - number of neutrons

number of protons = number of electrons
wrote...
11 years ago
The question is checking your understanding of atomic terms and definitions

Atomic mass = number of protons + number of neutrons -  You have the atomic mass
You have the number of neutrons.

Therefore: Number of protons = atomic mass- number of neutrons.

The number of electrons is equal to the number of protons.

So you are able to work out the answer.



.
wrote...
11 years ago
atomic mass=mo.of neutrons+no.of protons

if you know the atomic no.of that element it will become easy to find not only the no.of electrons but  
also it's E.C(electronic configuration)

Ian giving you a hint:
find your answer through this formula :



1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d
6s 6p
7s


Thankyou
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