Chapter 5

Quantum Numbers

Part 1

Quantum Numbers

• There are four quantum numbers that describe the properties of an electron and the “orbital” that it occupies within an atom.

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What are orbitals?

• The main division of energy for an electron within an atom is called the energy level or shell.

• The energy level (shell) is subdivided into distinct areas called sublevels (subshells).

• The sublevels are divided into orbitals. The orbitals are where the electrons are found.

• Each orbital can hold no more than a pair of electrons.

Four Quantum Numbers describe the following:

1. distance from the nucleus

2. shape of the orbital

3. 3-dimensional positioning of the orbital

4. direction of electron’s spin within the orbital

The First Quantum Number The Principal Quantum Number

• Abbreviated as “n”• n = 1,2,3...• Represents the

distance of an electron from the nucleus & the main energy level of the electron.

What else does the Principal Quantum Number (n) tell us?

• n = number of sublevels in the energy level.

What else does the Principal Quantum Number (n) tell us?

• n2 = number of orbitals in the energy level.

What else does the Principal Quantum Number (n) tell us?

• 2n2 = maximum number of electrons possible in the energy level.

n Energy level

# of sublevels

# of orbitals

Max # of electrons

1 1 1 1 2 2 2 2 4 8 3 3 3 9 18 4 4 4 16 32

The Second Quantum Number (Types of Sublevels)

• The second quantum number identifies the type of sublevel that the electron occupies.

• There are four types of sublevels in atoms.

• The sublevels are identified by the letters: s, p, d, f

“s” sublevel and “p” sublevel

p orbitals have a dumbbell shape

a s orbitals have a spherical shape

Types of sublevels

• There are four types of sublevels in atoms.• The sublevels are designated s, p, d, f.

n Energy level

# of sublevels

Sublevel types

1 1 1 1s 2 2 2 2s, 2p 3 3 3 3s, 3p, 3d 4 4 4 4s, 4p, 4d, 4f

The Third Quantum Number

• The third quantum number identifies the orbital that the electron is in.

• An orbital is an area within a sublevel that can hold up to two electrons.

An “s” sublevel has one orbital

A “p” sublevel has three orbitals

A “d” sublevel has five orbitals

An “f” sublevel has seven orbitals

The 4th Energy Level

• n = ?

The 4th Energy Level

• n = 4

The 4th Energy Level

• How many sublevels are present and what type are they?

• Four sublevels: s, p, d, f

The 4th Energy Level

• How many orbitals are present?

• n2 = (4)2 = 16

The 4th Energy Level

•What is the maximum number of electrons?•2n2 = 2(4)2 = 32

The Fourth Quantum Number “s”

• Also called the spin quantum number.

• Can be either +1/2 or -1/2.

• Specifies the direction of spin of the electron on its axis.

• Spins are designated up or down.

Electron Spin

• Opposite spins produce opposite magnetic fields.

+1/2 -1/2

What sublevel is the first to be filled with electrons?

O

Which sublevel listed contains orbitals of the highest energy? O

Finish Video

• Electron Arrangement and Bonding.

Homework

• Complete Chapter 5 Worksheet 1