# Quantum Numbers

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Slides 02 Chemistry Basics Le Gresley v02.pdf
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Okay, so let's talk about quantum numbers in a little bit more detail. We introduced the concept in the last lecture, where we talked about their importance in understanding where electrons were. But when we are building up electrons within the periodic table, and we are moving from left to right, and we are adding electrons, as we increase the groups, we go up the group from sodium on one side to the noble gases on the other, what we need to do is understand more about where the electrons are for each individual atom. So I introduced the idea of the principle quantum number, which has the letter n associated with it; the orbital quantum number, l; and also the magnetic quantum number, m. Okay? So what we are going to be doing now is to better understand how electrons are filling these orbitals as we go across the periodic table and also as we go down the periodic table. So we have a picture of where electrons need to go: obviously, nowhere near the nucleus; that's the preserve of the neutron and the proton. And we know how many electrons there should be in any atom of any element. But we now need to understand some way of telling us where the electrons will go. And there are three rules that we are using in this case to understand how this happens: the Pauli exclusion principle, the Aufbau principle, and also Hund's rule. And each of these will enable you to predict the electron configuration of any atom or ion. The Pauli exclusion principle states that in any atom, no two electrons may have a set of quantum numbers with the same values. But there is a problem. In a 1s orbital, there can be two electrons, so...

The lecture Quantum Numbers by Adam Le Gresley, PhD is from the course Chemistry: Introduction. It contains the following chapters:

• Quantum numbers
• The Aufbau Principle
• Hund's Rule
• Valence Electrons
• Formation of Ions
• Covalent Bonds

### Included Quiz Questions

1. -2,-1, 0, 1, 2
2. -1, 0, 1
3. 0
4. 1
5. -3, -2, -1, 0, +1, +2, +3
1. 1s2 2s2 2p6 3s2 3p6 4s2 3d6
2. 1s2 2s2 2p6 3s2 3p6 4s0 3d8
3. 1s2 2s2 2p6 3s2 3p6 3d6 4s2
4. 1s2 2s2 2p6 3s2 3p6 4s2 3d4 4p2
5. 1s2 2s2 2p6 3s2 3p6 3d4 4s2
1. CaCl2
2. CH3Cl
3. N2H4
4. CO2
5. AgCl