Electron Configuration

Electrons in Atoms

General Rules

Pauli Exclusion Principle

Each orbital can hold TWO electrons

with opposite spins.

General Rules

Aufbau Principle

Electrons fill the lowest energy orbitals first.

“Lazy Tenant Rule”

Energy levels overlapExpected order:

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f...Actual order:

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f...

RIGHTWRONG

General Rules

Hund’s Rule

Within a sublevel, place one e- per orbital before pairing them.

“Empty Bus Seat Rule”

Shorthand Configuration

S 16e-

Valence Electrons

Core Electrons

S 16e- [Ne] 3s2 3p4

1s2 2s2 2p6 3s2 3p4

Orbital Notation

Longhand Configuration

Orbital Notation

Shows the arrangement of electrons in orbitals within a sublevel. Use squares to represent orbitals. Arrow up represents 1 electron. Arrow up and arrow down represents 2

electrons.

O

8e-

Orbital Diagram

Electron Configuration

1s2 2s2 2p4

Orbital Notation

1s 2s 2p

© 1998 by Harcourt Brace & Company

sp

d (n-1)

f (n-2)

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67

Periodic Patterns

1

2

3

4

5

6

7

s

d

p

s

f

Electron Filling in Periodic Table

Li

2s1

H

1s1

He

1s2

C

2p2

N

2p3

O

2p4

F

2p5

Ne

2p6

Na

3s1

B

2p1

Be

2s2

H

1s1

Al

3p1

Si

3p2

P

3p3

S

3p4

Cl

3p5

Ar

3p6

K

4s1

Ca

4s2

Sc

3d1

Ti

3d2

V

3d3

Cr

3d5

Mn

3d5

Fe

3d6

Co

3d7

Ni

3d8

Cu

3d10

Zn

3d10

Ga

4p1

Ge

4p2

As

4p3

Se

4p4

Br

4p5

Kr

4p6

Rb

5s1

Sr

5s2

Y

4d1

Zr

4d2

Nb

4d4

Mo

4d5

Tc

4d6

Ru

4d7

Rh

4d8

Pd

4d10

Ag

4d10

Cd

4p1

In

5p1

Sn

5p2

Sb

5p3

Te

5p4

I

5p5

Xe

5p6

Cs

6s1

Ba

6s2

Hf

5d2

Ta

5d3

W

5d4

Re

5d5

Os

5d6

Ir

5d7

Pt

5d9

Au

5d10

Hg

5d10

Tl

6p1

Pb

6p2

Bi

6p3

Po

6p4

At

6p5

Rn

6p6

Fr

7s1

Ra

7s2

Rf

6d2

Db

6d3

Sg

6d4

Bh

6d5

Hs

6d6

Mt

6d7

Mg

3s2

Ce

4f2

Pr

4f3

Nd

4f4

Pm

4f5

Sm

4f6

Eu

4f7

Gd

4f7

Tb

4f9

Dy

4f10

Ho

4f11

Er

4f12

Tm

4f13

Yb

4f14

Lu

4f114

Th

6d2

Pa

5f2

U

5f3

Np

5f4

Pu

5f6

Am

5f7

Cm

5f7

Bk

5f8

Cf

5f10

Es

5f11

Fm

5f14

Md

5f13

No

5f14

Lr

5f14

La

5d1

Ac

6d1

1

2

3

4

5

6

7

s

d

p

s

f

Periodic Patterns

Period # energy level (subtract for d & f)

A/B Group # total # of valence e-

Column within sublevel block # of e- in sublevel

s-block

1st Period

1s11st column of s-block

Periodic Patterns

Example - Hydrogen

1

2

3

4

5

6

7

Periodic Patterns

Shorthand Configuration Core e-: Go up one row and over to the

Noble Gas. Valence e-: On the next row, fill in the #

of e- in each sublevel.

[Ar] 4s2 3d10 4p2

Periodic Patterns

Example - Germanium

Full energy level

1

2

3

4 5

6

7

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

Stability

Electron Configuration Exceptions

Copper

EXPECT: [Ar] 4s2 3d9

ACTUALLY: [Ar] 4s1 3d10

Copper gains stability with a full d-sublevel.

Stability (Honors Only)

Electron Configuration Exceptions

Chromium

EXPECT: [Ar] 4s2 3d4

ACTUALLY: [Ar] 4s1 3d5

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

Stability (Honors Only)

Stability

Ion Formation Atoms gain or lose electrons to become more stable. Isoelectronic with the Noble Gases. (No charge)

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

Stability

Ion Electron Configuration

Write the e- config for the closest Noble Gas

EX: Oxygen ion O2- Ne