Chapter 5 NotesElectron Models

Evolution of Electron Models• The first model of the electron was given

by J.J. Thompson—the electron’s discoverer. His was the “plum pudding” model.

The Rutherford Model• With Rutherford’s discovery of the

nucleus of an atom, the atomic model changed.

The Bohr Model• Niels Bohr introduced his model, which

answered why e- do not fall into the nucleus.

• e- orbit the nucleus in energy levels similar to the way the planets orbit the sun.

Bohr Model and Energy Levels• energy levels are like the rungs of a ladder—

you cannot be between rungs, just like an e- cannot be between energy levels.

• A quantum of energy is the

amount of energy it takes

to move from one energy

level to the next.

Quantum Mechanical Model• In 1926, Erwin Schrodinger used the new

quantum theory to write and solve mathematical equations to describe e- location.

The Quantum Mechanical Model, cont.• Previous models were based on physical

models of the motion of large objects.

• This model does not predict the path of e-, but estimates the probability of finding an e- in a certain position.

Where are the electrons?• In an atom, principal energy levels (n) can

hold e-. These principal energy levels are assigned values in order of increasing energy (n=1,2,3,4...).

• Within each principal energy level, e- occupy energy sublevels.

• There are as many sublevels as the number of the energy level (i.e., level 1 has 1 sublevel, level 2 has 2 sublevels, etc.)

Where are the electrons?• There are 4 types of sublevels (s,p,d and f).

• Inside the sublevel are atomic orbitals that hold the e-. Every atomic orbital can hold 2 e-.

Principle Energy Levels: 1, 2, 3, 4 ...

Sublevels: s, p, d, f

Orbitals: 1 for s, 3 for p, 5 for d, 7 for f.

Electrons: 2 for each orbital.

Orbital Shapes

s orbital = s sublevel (spherical)

+ +

px orbital py orbital pz orbital

= p sublevel(peanut)

D orbitals – fyi only(daisy)

Where are the electrons?• So how many electrons can each energy level

hold?

– Level 1 has an s sublevel=2 e-

– Level 2 has an s and a p sublevel=8e-

– Level 3 has an s, p and d sublevel=18e-

– Level 4 has an s, p, d and f sublevel=32e-

Electron Configuration

Electron Configuration• In the atom, electrons and the

nucleus interact to make the most stable arrangement possible.

• The ways that electrons are arranged around the nucleus of an atom is called the electron configuration.

Aufbau Principle• Electrons occupy orbitals of the lowest

energy first.

Pauli’s Exclusion Principle• An atomic orbital may have no more than two

electrons.

Hund’s Rule• When electrons occupy the same kind of

sublevel, one electron goes in each orbital before the second one goes in.

• Pauli Exclusion Principle

–Each orbital can hold only TWO

electrons with opposite spins.

Aufbau Principle

“Sports Spectator Rule” (fill the lower stands first)

Electrons fill thelowest energy orbitals first.

RIGHTWRONG

• Hund’s Rule “Empty Bus Seat Rule”

Within a sublevel, place one electron per orbital before placing a second electron.

Heisenberg Uncertainty Principle• Heisenberg concluded that it is impossible to make any

measurement on an object with out disturbing the object (at least a little).

• The principle states:

“It is fundamentally impossible to know precisely both the velocity and the position of a particle at the same time.”

O

8e-

»Orbital Diagram

• Electron Configuration

1s2 2s2 2p4

B. Notation

1s 2s 2p

• Abbreviated

S 16e-

S 16e- [Ne] 3s2 3p4

1s2 2s2 2p6 3s2 3p4

• Unabbreviated

© 1998 by Harcourt Brace & Company

sp

d (n-1)

f (n-2)

1234567

67

C. Periodic Patterns

s-block

1st Period

1s11st column of s-block

C. Periodic Patterns• Example - Hydrogen

1

2

3

4

5

6

7

C. 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

C. Periodic Patterns• Example - Germanium

• Electron Configuration Exceptions

– CopperEXPECT: [Ar] 4s2 3d9

ACTUALLY: [Ar] 4s1 3d10

D. Stability

Cr - [Ar]4s1 3d5Cu - [Ar]4s1 3d10

Valence Electrons• Electrons in the atom’s

outermost orbitals. • These are the electrons

that determine the atom’s chemical properties.

• The fewer valence electrons an atom holds, the less stable it becomes and the more likely it is to react.

Octets•When an atom has 8 electrons in its largest energy level it is said to have an octet. •This is the most stable and least reactive atom.

Lewis Dot Structures• An atom’s dot structure consists of the element’s

symbol, (represents the atomic nucleus and inner-level electrons), surrounded by dots representing the atom’s valence electrons.

• G. N. Lewis devised this method while teaching a college chemistry class in 1902.

• Example: Lithium • Atomic Number: 3• Electron Configuration: 1s22s2

• Electron Dot Structure: Li·

Practice• Carbon:

• Fluorine:

• Neon:

F:..

.C

::..Ne