- #1
gracy
- 2,486
- 83
Why the moment of inertia of a molecule about the bond axis is small enough to ignore ?
I really don't have any idea.Please guide me.Simon Bridge said:Try calculating it and see.
throughout the atom.But being more technical i think where center of mass is present.Bystander said:Where is the mass of an atom located?
"?" Back up. Describe the structure of an atom.gracy said:throughout the atom
sorry i think the nucleus contain all mass as electrons have negligible mass.Bystander said:"?" Back up. Describe the structure of an atom.
I normally calculate moment of inertia as total mass multiplied by distance square.Simon Bridge said:How do you normally calculate the moment of inertia?
What would the distribution of mass in a diatomic molecule look like - roughly?
about 1.75 fm.Bystander said:Better. What's the diameter of a typical nucleus, or has that been covered for you at all?
Sorry I didn't understand.Nuclear mass would depend on atom of which element we are taking.Bystander said:What's nuclear mass x 1/2 of that squared?
squared of what?Bystander said:1/2 of that squared?
Pick an atom.gracy said:Sorry I didn't understand.Nuclear mass would depend on atom of which element we are taking.
"What?" The nuclear diameter. That's an end point of a bond axis.gracy said:squared of what?
Sorry i am talking about a molecule.Here x-axis is bond axis.Bystander said:That's an end point of a bond axis.
Bystander is correct, the axis you have as your x-axis is one with a non-negligible moment of inertia. There would also be one perpendicular to this and the axis along the bond, which also has a non-negligible moment of inertia, this is why diatomic gases have two rotational degrees of freedom. The bond axis is that which joins the two nuclei.Bystander said:No, that is one of three rotational axes directed at right angles to one another through the center of mass of the molecule; the bond axis is the line connecting the nuclei of the two atoms, and is the one axis of the three that you're interested in for this problem.
No, your black line (the bond) is (lies along) the bond axis.gracy said:[QUOTE="Bystander, post: 4940685, member: 50"the bond axis is the line connecting the nuclei of the two atoms,
View attachment 76453
Now is x-axis bond axis?
That's what i mean. Is black line bond axis?Vagn said:No, your black line (the bond) is (lies along) the bond axis.
The black line joining the two blue atoms is the bond axis. Your diagram is confusing as the arrow suggests your x-axis is vertical and perpendicular to the bond.gracy said:That's what i mean. Is black line bond axis?
Vagn said:The black line joining the two blue atoms is the bond axis. Your diagram is confusing as the arrow suggests your x-axis is vertical and perpendicular to the bond.
That's better.gracy said:View attachment 76455
Right?
Now how to proceed further in order to get the answer .Vagn said:That's better.
here (in the image i have given)there are two atoms( after all i am referring to diatomic molecule)nuclear mass of which one?Bystander said:What's the maximum distance of the nuclear mass from that axis?
Bystander said:Both of them. How far are they from the axis you've drawn?
Sorry but i am not getting this post.Bystander said:This is the point of asking you what nuclear dimensions are; so, calculating moments of inertia for the three rotational axes of a molecule about its center of mass, you have two that square something of the same order of magnitude as the bond length (not half in general, because not all diatomic molecules are homonuclear), and a third moment that squares a distance the order of nuclear dimensions.