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Subshells and Orbitals

Timberlake LecturePLUS 2000

Quantum Mechanics

Describes the arrangement of electrons in atoms in terms of:

- Main or principal energy levels (n)
- Energy subshells
- Orbitals (space occupied within the atom)

Timberlake LecturePLUS 2000

Principal Energy Levels (n)

Contain electrons that are

- Close in energy
- Similar distance from nucleus
- Have values of n = 1, 2, 3, 4, 5, 6…..
- Maximum number of electrons = 2n2

n =1 2(1)2 = 2

n =2 2(2)2 =8

n=3

Timberlake LecturePLUS 2000

Energy Levels (Shells)

- A group of electrons in an atom all having the same principal quantum number (n)

n = 1, 2, 3, …

- The first shell (n = 1) is lowest in energy, 2nd level next and so on 1<2<3<4
- The number of electron in each shell is limited to 2n2

n = 1 2n2 = 2

n = 2 2n2 = ____

Timberlake LecturePLUS 2000

Energy Levels for Electrons

Some possible electron transitions for the first three energy levels are shown below. The negative value means that the electron in the atom has a lower energy than a free electron

Energy Level Energy, E

n=3 ___________________ (-) 2.420 x 1019 J

n=2 __________________ (-) 5.445 x 1019 J

n=1 __________________ (-) 2.178 x 1018 J

Timberlake LecturePLUS 2000

Learning Check S1

A. What energy change (J) takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?

B. What energy change (J) takes place when the electron moves from the third shell to the second shell?

Timberlake LecturePLUS 2000

Solution S1

A. What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?

1.634 x 10-18 J of energy must be absorbed.

B. What energy change takes place when the electron moves from the third shell to the second shell?

(-5.445 x 10-19J)-(2.2420 x 10-19 J) = -3.025 x 1019J will be emitted as electron falls from a higher to a lower energy state

Timberlake LecturePLUS 2000

Subshells

- Energy sublevels within energy level
- All electrons in a subshell have the same energy
- Designated s, p, d, f ..
- Sublevel energy: s

Timberlake LecturePLUS 2000

Electron Locations

Main

Energy

Levels Sublevels

n=4 4s, 4p, 4d, 4f

n=3 3s, 3p, 3d

n=2 2s, 2p

n=1 1s

Timberlake LecturePLUS 2000

Electrons Allowed

- All electrons in the same sublevel have the same energy.
- All 2s electrons have the same energy. All 2p electrons have the same energy which is slightly higher than the energy of the 2s electrons

s sublevel 2 electrons

p sublevel 6 electrons

d sublevel 10 electrons

f sublevel 14 electrons

Timberlake LecturePLUS 2000

Electron Configuration

- List of subshells containing electrons
- Written in order of increasing energy
- Superscripts give the number of electrons

Example: Electron configuration of neon

number of electrons

1s2 2s2 2p6

main shell subshell

Timberlake LecturePLUS 2000

Order of Filling

- Total energy of a subshell =

energy of the main shell + the subshell

- The 4s energy < 3d energy

4p ___

3d ___ (finishes the n=3 shell)

4s ___ (starts the n=4 shell)

3p ___

3s ___

2p ___

2s ___

1s ___

Timberlake LecturePLUS 2000

Writing Electron Configurations

H 1s1

He 1s2

Li 1s2 2s1

C 1s2 2s2 2p2

S 1s2 2s2 2p6 3s2 3p4

Timberlake LecturePLUS 2000

Periodic Table and Electron Configuration

- Find the element on the periodic table
- Use the order of filling indicated across each period

Groups 1-2 = s level

Groups 3-8 = p level

Transition = d level

Lantanides = f level

Timberlake LecturePLUS 2000

Learning Check S2

Indicate if each configuration is (1) correct or (2) incorrect for potassium. Give an explanation for selection of 1 or 2. Explain

why or why not?

A. 1s22s22p63s1 1 or 2

B. 1s22s22p63s23p6 1 or 2

C. 1s22s22p63s23p64s1 1 or 2

D. 1s22p83s1 1 or 2

E. 1s22s22p63s23p7 1 or 2

Timberlake LecturePLUS 2000

Solution E2

For phosphorus, indicate if each configuration is (1) correct or (2) incorrect. Explain why or why not.

A. 2, 2, 8, 5 2

B. 2, 8, 3 2

C. 2, 8, 5 1

D. 2, 6, 7 2

Timberlake LecturePLUS 2000

Learning Check S3

Using the periodic table, write the complete electronic configuration for each:

A. Cl

B. Sr

C. I

Timberlake LecturePLUS 2000

Solution S3

Using the periodic table, write the complete electronic configuration for each:

A. Cl

1s2 2s2 2p6 3s2 3p5

B. Sr

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2

C. I

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5

Timberlake LecturePLUS 2000

Learning Check S4

A. The final two notations for Co are

1) 3p64s2

2) 4s24d7

3) 4s23d7

B. The final three notations for Sn are

1) 5s25p24d10

2) 5s24d105p2

3) 5s25d105p2

Timberlake LecturePLUS 2000

Solution S4

A. The final two notations for Co are

3) 4s2 3d7

B. The final three notations for Sn are

2) 5s2 4d10 5p2

Timberlake LecturePLUS 2000

Orbital

- A 3 dimensional space around a nucleus in which electrons are most likely to be found
- Shape represents electron density (not a path the electron follows)
- Each orbital can hold up to 2 electrons.

Timberlake LecturePLUS 2000

p subshell contains p orbitals

Timberlake LecturePLUS 2000

d orbitals

Timberlake LecturePLUS 2000

Learning Check S5

A. Number of electrons in a p orbital

1) 1e 2) 1e or 2e 3) 3e

B. Number of orbitals in a p subshell

1) 1 2) 2 3) 3

C. Number of orbitals in 4d subshell

1) 1 2) 3 3) 5

D. Number of electrons (maximum) in a 3d subshell

1) 2e 2) 5e 3) 10e

Timberlake LecturePLUS 2000

Solution S5

A. Number of electrons in a p orbital

2) 1e or 2e

B. Number of orbitals in a p subshell

3) 3

C. Number of orbitals in 4d subshell

3) 5

D. Number of electrons in a 3d subshell

3) 10e

Timberlake LecturePLUS 2000

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