# Quantum Number and Electron Configurations The arrangement of

Quantum Number and Electron Configurations The arrangement of electrons in an atom

Quantum Numbers n n Scientists use quantum number to describe the probable region for finding an electron There are 4 quantum number.

The Principle Quantum Number n n Symbolized by n Indicates the main energy level occupied the electron (the ring away from the nucleus) Values of n are positive integers (1, 2, 3, 4) As n increases, so does the distance from the nucleus as well as the electron’s energy.

Angular Momentum Quantum Number n n n Represented by l Represents the shape or type of orbital that corresponds to a particular suborbital l=n-1, n-2, n-3, up to n-n So, if n = 3, l can equal 2 , 1 and 0 Each of these numbers is given a letter. We will only deal with the first four letters. 0=s, 1=p, 2=d, 3=f

Magnetic Quantum Number n n n Represented by m This a subset of l Indicates the number and orientations of orbitals around the nucleus It is equal to all of the integers from –l to +l So, if l = 2, then m = -2, -1, 0, 1, 2

The shapes that result are on Page 96

Spin Quantum Number n n n Symbolized by +1/2 and -1/2 or and Indicates the orientation of the electrons’ magnetic field Also known as spin

How many electrons can each level hold? n The formula used to calculate the number of electrons each level can hold is 2 n 2 Level # 1 2 3 4 5 6 7 Theoretical 2 8 18 32 50 72 98 Practical 2 8 18 32 32 18 8

So, those are the Quantum Numbers But what do they mean? The answer is in something called electron configurations

Aufbau Principle n n How did you decide where to send the people at the Hotel Californium? “Each electron occupies the lowest energy orbital available” n Lowest Energy s 1 p 3 Highest Energy d 5 f 7

Orbital Filling Sequence and Energy Levels From Glencoe – Chemistry: Matter and Change

Pauli Exclusion Principle n n “One person to a bed” “A maximum of two electrons may occupy a single orbital sublevel, but only if the electrons have opposite spins”

Hund’s Rule n n The Family Situation “Single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital. ”

What does that mean in English? n n Much like the family at Hotel Californium, electrons will space each other out as much as possible before occupying spaces close to other electrons. Here’s another way to think about it: How do strangers sit on a bus as it fills up?

With all this talk about electrons, here is a review question? Where can we find out how many electrons an atom has?

Now we know the rules and the number of electrons, what do we do with them?

Remember this from earlier? Example: Chlorine Electrons? 17 Electron configuration: 1 s 2 2 p 6 3 s 2 3 p 5 Lowest Energy to Highest Energy From Glencoe – Chemistry: Matter and Change

So, if you had the orbital filling sequence, can you fill in the electrons? n 1 s, 2 p, 3 s, 3 p, 4 s, 3 d, 4 p, 5 s, 4 d, 5 p, 6 s, 4 f, 5 d, 6 p, 7 s, 5 f, 6 d, 7 p Let’s take Cl again. Cl has 17 electrons. 1 s 2 s 2 p 3 s 3 p Writing it without the boxes: 1 s 2 2 p 6 3 s 2 3 p 5 Orbital diagram Electron Configuration

How can I remember all of those numbers and letters? s 1 2 3 4 5 6 7 p d f The Diagonal Rule X X 2 3 4 5 6 7 X X 3 4 5 6 7 X 1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p 5 s 4 d 5 p 6 s 4 f 5 d 6 p 7 s 5 f 6 d 7 p X 4 5 6 7 X X 5 6 7 7

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