So electrons that are near the nucleus behave this way or all electrons at all times?
electrons are quantummechanical objects, and hence will reveal a behaviour depending on the experiment they're subjected to: this is a consequence of the wave/particle dualism.
Choose an experiment where the "particle type" side of their nature is forced (for example, a cathode-ray tube) , and you might even generate TV-pictures from that
Choose a different experiment, for example the vicinity of an atom's nucleus, and the wave-type behaviour will be forced
Choose a mixed experiment, and mixed behaviour will result (i.e. fire single electrons from a cathode - ray tube at a double slit experiment: though you will observe single, located "hits" at the detector, nevertheless with several shots their local distribution will show a wave-interference picture
Now if you will, pretend I am a small child. (...)
If I had to explain this to a child, I usually would use a picture (of which I know that it's not completely correct, but will reveal the gist of the effect nevertheless) or "experiment" like this: I would show the child a coin, and make it look at the two different pictures backside and front.
The child will agree that each of the pictures can be recognized clearly, and that they are different from each other, but nevertheless are "two sides
of the same coin": it will accept that things can have "two natures", depending of the way
we observe them.
Then I will take that coin, put it upright on a table, and make it turn very fast. I then will ask the child what it sees, esp. which of the two pictures it will see, and the answer will be: none of the pictures (as it's turning too fast)
That's how I teach "dualism" to the child: its like a fast turning coin, and insofar "undecided" with respect to either side. Only if we "force" the coin to make a decision (i.e. if it falls down flat) it will reveal one of its two natures, depending on the physics in the moment it falls down.
Finally, where can I find the mathematical formula for an electrons location?
In the classical sense, you can't, if it came to electrons in atoms, as under the influence of this experiment they become undefined both in space and time (though the "time" part usually is neglected in discussion, as this is even more strange than the "place" part. However, you can even see
this in experiments, as electrons in a certain sense "seem to know" the experiment they will be subjected to
in a future, that however still didn't happen (in our "human" sense), beforehand. Very strange, disturbing and mind boggling, I agree )
... and if you wish to find the mathematical formula for
the equivalent for a "location" with wavefunctions, you'll need to look into quantum mechanics, or even quantum electro dynamics (if you wish to learn about this under relativistic conditions)
maybe you'll find something, that in your perception will satisfy for a "location" there
I didn't
ref. literature: Wikipedia might give you a first impression of what you're up to and against, if you wish to go for it anyway, and has a lot of usefull notes and references at the end, as usual
http://en.wikipedia.org/wiki/Quantum_mechanicshave fun, study, do research ... and maybe come up with something more usefull for the next generations than the what we old farts could provide to you
regards
Ingo