Dalton Model

1803 – John Dalton believed that an atom was an indestructible particle with no internal frame.

(Billiard Ball Model)

Thomson Model

1897 – J.J. Thomson discovers the electron. He believed electrons were embedded in positive charge sphere.

(Plum pudding Model)

Rutherford Model

1911 – Ernest Rutherford discovers that there is a dense, positively charged nucleus. Electrons go around the nucleus.

Bohr Model

1913 – Niels Bohr enhances Rutherford’s model by having electrons move in a circular orbit at fixed distances from the nucleus.

The Evolving Atomic Model

Electrons in an Atom• According to the Bohr Model, electrons

(e-) can only orbit the nucleus in specific, allowed pathways.

• They move toward and away from the nucleus by “steps” or discrete amounts of energy (a quantum) that are released or absorbed.

• e- farther from the nucleus have more energy. Those closer to the nucleus have less energy.

• Very similar to a ladder. Just as you cannot step on the air between the rungs, an electron cannot exist between the levels.

• Ground state: the lowest energy of an atom

• Excited state: higher potential energy state

• Energy absorbed e- moves to higher state

• Energy emitted e- moves to lower state

Higher excited state

Excited state

Ground state

Excited state

Ground state

EnergyEnergy

Hydrogen’s Line Emission Spectrum

Excited State

Ground State

Energy (Light)

Turn this sideways and it looks like a ladder

Quantum Mechanical Model

• In 1926, Erwin Schrödinger developed an equation that described the behavior of an e- :

Eψ(x) = [-(h2/8π2m)d2/dx2 + V(x)] ψ(x)

(Don’t worry, you don’t need to know this!!!)

• He believed:– Electrons are found in discrete

energy levels (as Bohr believed)

– BUT, the electron does not move around the nucleus in a fixed orbit

Ex: propeller blade

This all led to the modern quantum theory …

Modern Atomic TheoryModern Atomic Theory1. Orbitals describe the three dimensional

space that electrons occupy.

2. The location of an electron can only be described by probability. (ex. You in this classroom and your parents are looking for you.)

3. Orbitals give shape to the atom.

• These properties allow us to describe electrons in terms of their energy and position.

• Ahhh Yes….. Quantum Mechanics!

OrbitalNot anOrbit

Quantum MechanicsQuantum Mechanics….Sounds Scary!!!!

Think of it this way…

It is the “address” of an electron

Did you ever mail a letter?• Where do you live? (4 things)

- State

- City

- Street Name

- House Number

• Electrons are identified the same way (4 things)…

- Principle (identified by 1,2,3,4)

- Orbital (identified by s, p, d or f)

- Magnetic

- Spin

Abby Lehman346 W. Palm Street

Los Angeles, CA 13543

Four Quantum Numbers1. Principle Quantum Number

• Indicates the main energy level occupied by the e- (distance from the nucleus)

• Shell Number (1st shell is closest to nucleus, 2nd is further, and so on …)

• Values of n can only be positive integers (1, 2, 3, etc.)

2. Orbital Quantum Number • Indicates the shape of the orbital (actual 3D space

where the probability of finding e- is greatest)

• Sublevel of n

• Designated s, p, d, f

s

p

d

1 2 3

• s sublevel

– Spherical shaped

– One orbital

– Holds two e-

• p sublevel

– Peanut or dumbbell shaped

– Three orbitals

– Holds six e-

• d sublevel

– Double peanut shaped

– Five orbitals

– Holds ten e-

• f sublevel

– Flower shaped

– Seven orbitals

– Holds fourteen e-

There are a few rules that help us represent the arrangement of electrons in atoms

address• Aufbau (“building up”) principle: an electron

occupies the lowest energy possible

• Hund’s rule: orbitals of equal energy are each occupied by one electron before accepting a second electron

• Pauli exclusion principle: no two electrons in the same atom will have the same set of quantum numbers (no two fans have the same seat)

e-

How do you write this address How do you write this address for the electron?for the electron?

To write electron configurations, you need to know:

1. Period # 1 – 7 (exception for d orbitals – 1 less)

2. Subshell letter (e.g. s, p, d, f…)

3. Atomic # is # of e- as an exponent

Electron Configurations – Quick addressElectron Configurations – Quick address

ss dd pp

ff

Example

Sulfur = 1s22s22p63s23p4

Study guide for chp. 4 and 5Atomic structure notes

-Know how to calculate atomic mass

-Know how to draw bohr modelReview worksheets 4.1-4.3Know what ion an element will formQuantum mechanics notesKnow how to write long hand electron configurationBe able to explain the behavior of electrons (i.e., what did you learn from the flame lab?)Review worksheets 5.1-5.2

Need to add

Relate outer shell to lewis dot and oxidation states