Quantum Number and

Electron Configurations

The arrangement of electrons in an atom

Quantum Numbers

Scientists use quantum number to describe the probable region for finding an electron

There are 4 quantum numbers.

The Principle Quantum Number

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 Represented by l Represents the shape or type of orbital

that corresponds to a particular suborbital

Each of these numbers is given a letter. We will only deal with the first four letters.

s, p, d, f

Magnetic Quantum Number

Represented by m Indicates the number and orientations

of orbitals around the nucleus This will tell us how many boxes to

make for each type of orbital when completing orbital diagrams

The shapes that result are on Page 96

Spin Quantum Number

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? The formula used to calculate the number

of electrons each level can hold is 2n2

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

How did you decide where to send the people at the Hotel Californium?

“Each electron occupies the lowest energy orbital available” Lowest Energy Highest Energy

s p d f1 3 5 7

Orbital Filling Sequence and Energy Levels

From Glencoe – Chemistry: Matter and Change

Pauli Exclusion Principle

“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

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?

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?

In other words…

SPREAD THEM OUT!!!

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?

From Glencoe – Chemistry: Matter and Change

Example: Nitrogen

Electrons? 7

Electron configuration:

1s2 2s2 2p3

Lowest Energy to Highest Energy

So, if you had the orbital filling sequence, can you fill in the electrons?

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

1s 3s2p2s 3p

Now, let’s take a look at Cl.

Cl has 17 electrons.

Writing it without the boxes: 1s2 2s2 2p6 3s2 3p5

Orbital diagram

Electron Configuration

How can I remember all of those numbers and letters?

1

2 2

3 3 3

4 4 4 4

5 5 5 5 5

6 6 6 6 6 6

7 7 7 7 7 7 7

s d fpThe Diagonal Rule

2s1s 2p 3s

4d 5p 6s

3p 4s 3d 4p 5s

4f 5d 6p 7s 5f 6d 7p

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X

X

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