# Chapter 15 - Electrons in atoms

In the classical model of an atom, why can't electrons escape from the nucleus, or fall into it?
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- The three spatial quantum numbers act as the polar coordinates for the orbital, labelling it and telling us what shape it is.
> "n" is the radial quantum number, and tells us which shell an electron is in.
> "l" is the angular quantum number, which tells us which orbital an electron is in. (0 = s orbital, 1 = p orbital, 2 = d orbital, 3 = f orbital)
> "m" is also an angular quantum number, and it tells us which direction an orbital is pointing in. If there is a 3p orbital where m=0 and another where m=1, these two orbitals are pointing in opposite directions.

- "s" is the spin quantum number, which measures the time evolution of the wave.
As a general rule, the more maxima and minima that an orbital has (and therefore the more nodes), the shorter the wavelength and the higher the energy.

- For a wave in a one-dimensional box, each allowed wave has (n-1) nodes.
- For a wave on a circle, each allowed wave has l nodes.
- For a wave localised in an atom (ORBITALS), each allowed orbital has a total of (n-1) nodes; l angular nodes and (n-l-1) radial nodes.

This means that an electron in a higher shell will have more energy than one in a lower shell, as "n" will be higher so the number of nodes will be also.