# Finding number of atoms and volume

fernanhen

## Homework Statement

The mass of a copper atom is 5.30 10-25 kg, and the density of copper is 8 920 kg/m3 .
(a) Determine the number of atoms in 1 cm3 of copper.

_______Cu—atom/cm3

(b) Visualize the one cubic centimeter as formed by stacking up identical cubes, with one copper atom at the center of each. Determine the volume of each cube.

_______cm3/Cu—atom

(c) Find the edge dimension of each cube, which represents an estimate for the spacing between atoms.

_________cm

## Homework Equations

Density=mass/Volume

## The Attempt at a Solution

Well, the book the book we are using for this class "Physics for Scientists and Engineers" by Serway has no right being used in an Introductory Physics class.

I re-read the relevant chapter THREE times and still haven't figured out how to solve this.

Therefore, I used my intuition alone.

Using the info I have:

3.06*10^(-25)kg= (8,920kg/m^3)*1cm^3 = M=D*V

I cancelled the volumes but that won't left over any missing variables.

I googled for alternatives and my textbook absolutely does not point us in any direction regarding this question. Please help.

## Answers and Replies

Homework Helper
Gold Member
You need the answer from a) to do b) and c). So focus on that first. It is essentially a unit conversion problem.

fernanhen
You need the answer from a) to do b) and c). So focus on that first. It is essentially a unit conversion problem.

Yes, I just figured that this morning. Thanks.

But now I am having trouble with that.

I equated:

(8920kg/m^3)*(m/cm)*(cm-atom)/kg=Cu-atom/cm^3

Then 8920/m^3*1m/100*5.24*10^(-27)=Cu-atom/cm^3

But now what? Does my setup even look right?

Homework Helper
Gold Member
I equated:

(8920kg/m^3)*(m/cm)*(cm-atom)/kg=Cu-atom/cm^3

Then 8920/m^3*1m/100*5.24*10^(-27)=Cu-atom/cm^3

But now what? Does my setup even look right?

Not really. You need to inventory all of your unitary conversion factors and apply them correctly.
1 = 1 Cu atom / 5.30 10-25 kg
1 = 1m3 / 1x106 cm3
1 = 8920 kg / 1m3

You are trying to convert 1 cm3 [of Cu] to Cu atoms. If you had a unitary conversion factor
in the form of:
1 = X Cu atoms / Y cm3 you would be close to being finished with part a). Can you try this using the above unitary factors?

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