C. Johannesson IV. Electron Configuration (p. 105 - 116, 128 - 139) Ch. 4 - Electrons in Atoms

C. Johannesson

IV. Electron Configuration(p. 105 - 116,

128 - 139)

Ch. 4 - Electrons in Atoms

Pauli Exclusion Principle

1. Principal # 2. Azim(Ang. Mom.) # 3. Magnetic # 4. Spin #

energy level

sublevel (s,p,d,f)

orbital

electron

No two electrons in an atom can have the same 4 quantum numbers.

Each e- has a unique “address.”

A. General Rules

Pauli Exclusion Principle

Each orbital can hold TWO electrons

with opposite spins.

Spin is the only difference between

these two electrons’ quantum states.

O 8e-

Orbital Diagram: shows all the electrons in an atom as arrows. Each box is an orbital. Joined orbitals are sublevels.

B. Notation

1s 2s 2p UP arrows have a ms of +1/2

DOWN arrows have a ms of -1/2

C. Johannesson

A. General Rules

Aufbau Principle

Electrons fill the lowest energy orbitals first.

“Lazy Tenant Rule”

RIGHTWRONG

A. General Rules

Hund’s Rule

Within a sublevel, place one e- per orbital (spin-parallel) before pairing them.

“Empty Bus Seat Rule”

1s1Just one electron in the 1s sublevel.

1

2

3

4 5

6

7

C. Electron Configuration

Gives the energy state for ALL the electrons in an atom.

Hydrogen’s configuration is simplest and shortest because H only contains one electron.

1s2

C. Electron Configuration

Gives the energy state for ALL the electrons in an atom.

Lithium contains 3 electrons: 2 in the 1s

(#1 & #2) 1 in the 2s

(#3) 2s1

1 23

1s2Sulfur’s last 4 electrons are in 3p.

C. Electron Configuration

Gives the energy state for all the electrons in an atom.

Sulfur’s configuration needs to include ALL 16 of its electrons.

1 23 4 5 6 7 8 9 10

11 12 13 14 15 16

2s22p63s23p4

All e-configs start at 1s.Powers should add up to atomic #

(2+2+6+2+4=16)

C. Johannesson

O 8e-

Orbital Diagram

Electron Configuration

1s2 2s2 2p4

B. Notation

1s 2s 2p

C. Johannesson

Shorthand (Noble Gas) Configuration

S 16e-

Valence ElectronsCore Electrons(up to previous Noble)

S 16e- [Ne-10] 3s2 3p4

1s2 2s2 2p6 3s2 3p4

B. Notation

Longhand Configuration

C. Johannesson

1

2

3

4

5

6

7

C. Periodic Patterns

Aufbau Principle: electrons always fill in order from lowest energy to highest energy.

Atomic numbers on the periodic table count electrons in the order they fill, so the order is always the same.

Don’t forget where the f-block goes!

C. Periodic Patterns

Aufbau Series: the order in which electrons fill energy levels & sublevels.

3p64s21s2 2p63s2 4p63d102s2

…5p6 6d10

4d10...4f146s2 5d10

5s2

7p66p6 7s2 5f14

C. Periodic Patterns

Orbital diagrams show the same information as electron configuration in a different way.

The Aufbau Series still applies!

1s2

C. Electron Configuration

Example – Nickel (Ni #28)

Ni

1 2

2s22p63s23p64s23d8

3 4 5 6 7 8 91011 12 13 14 15 16 17 18

19 20 21 22 23 24 25 26 27 28

2+2+6+2+6+2+8 = 28

C. Johannesson

1

2

3

4

5

6

7

C. Periodic Patterns

Shorthand Configuration Core e-: Start with the noble gas from

the previous period. Valence e-: On the next row, fill in the #

of e- in each sublevel.

C. Johannesson

[Ar-18]

1

2

3

4 5

6

7

4s2 3d10 4p2

C. Periodic Patterns

Example - Germanium

C. Johannesson

C. Periodic Patterns

Period # energy level (remember d & f don’t line

up with s & p!)A/B Group #

total # of valence e-

Column within sublevel block # of e- in sublevel

C. Johannesson© 1998 by Harcourt Brace & Company

s p

d (n-1)

f (n-2)

1234567

67

C. Periodic Patterns

C. Johannessons-block1st Period

Hydrogen: 1s11st column of s-block

1

2

3

4 5

6

7

C. Periodic Patterns

Elements in the same column have similar valence configurations.

s-block5th Period

[Kr-36]5s11st column of s-block

1

2

3

4 5

6

7

C. Periodic Patterns

Rubidium (Rb #37)

C. Johannesson

Full energy level

1

2

3

4 5

6

7

Full sublevel (s, p, d, f)Half-full sublevel

D. Stability

C. Johannesson

Electron Configuration Exceptions

Copper

EXPECT: [Ar] 4s2 3d9

ACTUALLY: [Ar] 4s1 3d10

Copper gains stability with a full d-sublevel.

D. Stability

C. Johannesson

Electron Configuration Exceptions

Chromium

EXPECT: [Ar] 4s2 3d4

ACTUALLY: [Ar] 4s1 3d5

Chromium gains stability with a half-full d-sublevel.

D. Stability

C. Johannesson

1

2

3

4 5

6

7

D. Stability

Ion Formation Atoms gain or lose electrons to become

more stable. Isoelectronic with the Noble Gases.

C. Johannesson

O2- 10e- [He] 2s2 2p6

D. Stability

Ion Electron Configuration

Write the e- config for the closest Noble Gas

EX: Oxygen ion O2- Ne