Question

Which characteristic is given by the principal quantum number?
a. orbital size
b. orbital mass
c. orbital shape
d. orbital orientation

Answer 1

This may help
http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Quantum_Mechanics/10%3A_Multi-electron_Atoms/Quantum_Numbers

Answer 2

I'd vote for a) because the principal quantum number n describes the "orbital shell" you're in. For example hydrogen: nlm = |100> while for i.e. Lithium the possible nml = |1 0 0>, |2 0 0>, |2 1 -1>, |2 1 0>, |2 1 1>
or in a maybe more familiar chemical notation hydrogen: 1s while Lithium is 1s2 2s1

The principal number n in this case marks the "size" of the shell (its energy lvl to be precise) while the angular quant. num. l determines the shape. The magnetic quantum number m would describe the projection of angular momentum on z axis and thus definitively set the orientation of the orbital.

For hydrogen solutions these orbitals look like:
http://3.bp.blogspot.com/-jq0Ock6-yAk/Uwo3ot5qGPI/AAAAAAAAC6A/QIXbgrp0ZMs/s1600/Screen+Shot+2014-02-21+at+9.32.42+AM.png

of course hydrogen itself only has the first |0 0 0> configuration in ground state.

Answer 3

ah, I said why not the shape and orientation, but forgot to comment why not mass.
b) is also semi-possible if you take it means the mass of the electron and not the orbit per say. Then yes because the mass of the electron is tied to its energy levels by the deBroglie relationship.

However the question asks specifically why "orbital mass" and I don't know what that is so I think it's just a "distraction" answer

Answer 4

I think it's a. I think that this is how the radius of the hydrogen atom was/is calculated, but putting the principal quantum number equal to 1 for a 1 proton 1 electron system - ie hydrogen. Orientation is dealt with in the sub shells.
http://perendis.web.com

Answer 5

The bloke whose name is associated with previous entry is Niels Bohr, Danish Nobel physicist. His name is also given to the "Bohr radius" which is the value when the principal quantum number is. I think.
In terms of orientations, in the subshells they can point along the xyz axes, of they can point at angles to all three axes. I think that that is the m value.