Question

Why do they say quantum numbers are like an address?

Answer 1

Let's look at a regular address as an example:

1009 South Main
Apt. 21
Houston, TX
77531

There are four quantum numbers.

The first quantum is the "n" number. It is called the principal quantum number and corresponds to the size and energy of the orbital. It is the "ring". If you are referring to the energy level of electrons closest to the nucleus, your 1st quantum number is 1. Second energy level = 2, etc. Thus the city (Houston, TX)

The second quantum number is the "l" number and refers to the shape of the atomic orbital. The "l" number is the angular momentum quantum number. Here's how this number breaks down:
s = 0
p = 1
d = 2
f = 3 etc.
This is like the zip code. The "l" quantum number specifies the shape of the orbital.

The third quantum number, (m l), is related to the orientation in space relative to the other orbitals (ex: along the x, y, or z axes). This quantum number can range from -l through 0 to + l. In an address, this could be the street address.

The fourth quantum number represents spin. When you have paired electrons, they have opposite spins. Scientists have assigned +1/2 or -1/2 as spins. (sometimes called spin up or spin down). This could be like the apartment number above.

Good luck!!