AP Chemistry Help NEEDED Right away please?

D

The answer is D.

Why? Because, electrons move so fast around the nuclei that its hard to see this electron cloud and determine just exactly how big the atom is.

d
the electron cloud surrounding the nucleus are not fixed and therefore there is no definite outer edge

The answer IS.....D.  

But lets clarify why.   We know them electrons zip around too fast for anyone to see.  It makes a cloud in fact.  But the real reason we can't DETERMINE the outer edge of an atom is because the tool we use (Atomic Force Microscope) is inherrently blurry.  Its like this......rub your finger across your arm.......notice much?  Probably not, cause your finger is so big it cancels out all the quantum jitteriness, as well as thermal jitteriness, so you just feel a somewhat "smooth" arm.  But for an AFM which has a finger the size of one atom, when we bring this within the very very very tiny distance away from our isolated atom, we get electonic and magnetic events that occur.  And you know how magnets can cause electricty, which then causes more magnetics, which then causes more electricity, which then causes more magnetics, etc., etc....well to the computer trying to interpret the data from the AFM finger, there is always some static that results from this electromagnetic interference.  Thats why atom pictures always look smeary, or fuzzy and stretched.  Maybe you can figure out how to fix that one day.   It has alot to do with the fact that we have to use a vacuum environment to use AFM.

Sure, we CANNOT call an electron fixed, but its ORBIT sure is.....What do you think Schrodinger's Equation generalizes?  or Dirac's correction?  Quantum Mech says the orbitals have BOUNDARY surfaces, distances beyond which the probability of findind an electron is soooooooo small it IS zero.  So, we COULD say atoms are as big as earth, cause the unfixed electron can, via quantum tunneling, end up near the moon, but that's just going too far.  We cannot determine atomic size DEFINITIVELY because our vacuum environment, Atomic Force Probes, cannot accurately recreate the detected positions of the electron, or I should say Model them, due to interference.  A 3s Orbital is a 3s orbital, and we can calculate its dimensions, but we cannot DIRECTLY MEASURE IT, but it is still there.  Its like saying Just cause my hair stands on end when your finger is electrified, that my head has no shape!!!!!!   yes it does.  You just cant determine it due to something "wrong" with your finger (too much electrostatic charge)/