Finding the volume of one water molecule

  • Context: Chemistry 
  • Thread starter Thread starter Niles
  • Start date Start date
  • Tags Tags
    Molecule Volume Water
Click For Summary

Discussion Overview

The discussion revolves around the challenge of calculating the volume of a single water molecule, with participants exploring different approaches and methods. The scope includes theoretical reasoning, mathematical reasoning, and homework-related inquiries.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant, Niles, initially suggests using the molar mass and densities of hydrogen and oxygen to find the volume of one water molecule, but encounters issues with the calculation.
  • Another participant advises starting with the density of water and calculating the number of molecules in a given volume, arguing that summing the volumes of individual atoms is likely to yield incorrect results.
  • Niles acknowledges a mistake in the units of volume, clarifying that the volume should be in cubic meters (m³) instead of kilograms (kg³).
  • A later reply emphasizes that the approach of adding atomic volumes is flawed due to the overlapping volumes of atoms when they bind, and mentions that calculating molecular volume from atomic volumes is complex and not straightforward.
  • Niles concludes that using the density method is the appropriate approach to determine the volume of the water molecule.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method for calculating the volume of a water molecule, with multiple competing views on the validity of different approaches remaining throughout the discussion.

Contextual Notes

Participants express uncertainty regarding the generalizability of methods for calculating molecular volume from atomic volumes, noting that overlapping volumes complicate the process. There is also a lack of clarity on the assumptions necessary for different methods.

Niles
Messages
1,834
Reaction score
0

Homework Statement


Hi guys

I know the molar mass (i.e. g/mole) of H and O, but from this, then how do I find the volume of 1 water molecule? I know the densities of H and O as well, from which I can find the volume of H and O. Do I just add these, one of V_oxygen and two of V_hydrogen (I know the correct value is 2.99E-29 kg^3)? I tried doing this, but it did not give me the correct value.


Niles.
 
Physics news on Phys.org
You better start with water density (1g/mL) and calculate how many molecules in 1mL. Assuming final volume of a molecule is a sum of volumes of atoms is a sure way of getting it wrong.

How come final answer is in kg3? You sure you didn't mean m3?

--
 
I mixed it up - the volume is of course in m^3. Regarding the density, then what I wanted was a general way of doing it, because I might not always know the density of the molecule as a whole, but only each atomic-part of the molecule.

So, how should I do it? I can find V_H and V_O, but adding them as 2V_H + V_O doesn't give me the correct result.
 
Niles said:
So, how should I do it? I can find V_H and V_O, but adding them as 2V_H + V_O doesn't give me the correct result.

That's because this is a faulty approach. When atoms bind their volumes partially overlap.

And I am not aware on any general method that will let you calculate volume of the molecule from the volumes of atoms involved. It just doesn't want to be that easy. You can try to calculate molecule shape using Schroedingers equation and quantum chemistry methods, but it is not an easy task.
 
Ok, then the "density-method" is the way to go. Thanks!Niles.
 

Similar threads

  • · Replies 21 ·
Replies
21
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 2 ·
Replies
2
Views
9K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 9 ·
Replies
9
Views
3K