Solving Ge-Si Alloy & Doping P in Si - Question 6

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Homework Statement


Question 6. Germanium forms a substitutional solid solution with silicon.
(a) Compute the number of germanium atoms per cubic centimetre for a Ge-Si alloy that contains 25 w/o Ge and 75 w/o
Si.
(b) If, instead, phosphorus is added to Si to dope the material n-type at a doping of 1018/cm3, determine both the w/o and
a/o of P in the Si.

I have no idea how to do this question, what the question wants me to do, or w/o and a/o even mean. Can anyone can please put me on the right track, or even a track for starters, as this stuff is completely new to me and I have no idea. Not even where to start. Any help much appreciated, I have callister 7ed. if anyone knows where to find it, in that book.
 

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Weight percent and atomic percent, presumably. That's all in Callister
 
You can find the mass density of the elements. You know Avogadro's Number.

Use the density definition of mass over volume.
 
ok, i got told this today... sorry i have no idea what avagadros number is... i looked it up, and something to do with chem... I've never done this before... ok, density is mass over volume, yes... mass am i meant to know this? get it from the table of elements? ge is 32 and si is 14... is that their mass? in that atomic u unit? then how am i meant to find the volume?? are they in a box or something?? I just don't know... could you maybe tell me, where in the book, i mite find examples of this? because our lec notes are awful, very vague... and i have no prior knowledge of chem what so ever.
 
If you have Callister, read the first chapter. Atomic percent is the number of atoms of the solute divided by the total number of atoms. Weight percent is the weight of the solute divided by the total weight. The atomic mass is the number of grams per mole of an element (i.e., per Avogadro's number of atoms of the element).