1. Models of the Atom
Foothill Chemistry

2. Let’s Talk About Models
When things are too large, too complex, too expensive, or unable to be studied at actual size.
Help us to understand what we want to know.

3. Rutherford’s Model
Rutherford’s Model could not explain the photoelectric effect or chemical properties of atoms

4. Bohr Model
Electrons are not found just anywhere surrounding the nucleus, but in specific circular paths, or orbits around the nucleus.

5. Bohr Model
Each possible electron orbit in Bohr’s model has a fixed energy.
The fixed energies an electron can have are called energy levels.
A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level.
Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced.
The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level.

6. Electron Cloud Model
Erwin Schröedinger used mathematical models to develop it.

7. Quantum Mechanical Model
The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.
Heisenberg Uncertainty Principle – It is impossible to determine simultaneously the position and velocity of an electron or any other particle.
The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.

8. Atomic Orbitals
An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron.
Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.
Orbital shapes have different letters – s, p, d, and f

9. Atomic Orbitals
An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron.
Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.
Energy sublevels are represented by letters - s, p, d, and f
Each sublevel has a different shape. The different shapes are represented by corresponding numbers 0-3

10. s and p Orbitals
Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped.

11. d Orbitals
Four of the five d orbitals have the same shape but different orientations in space

12. Energy Sublevel Configurations
The number and kind of atomic orbitals depend on the energy sublevel
Principal Energy Level
Number of Sublevels
Type of Sublevel
n=1 1
1s (1 orbital)
n=2 2
2s (1 orbital), 2p (3 orbitals)
n=3 3
3s (1 orbital), 3p (3 orbitals), 3d (5 orbitals)
n=4 4
4s (1 orbital), 4p (3 orbitals), 4d (5 orbitals), 4f (7 orbitals)

13. Electrons and Orbitals
Each orbital can only hold a maximum of two electrons
Energy Level n
Maximum Electrons 1 2 8 3 18 4 32

14. Quantum Numbers Principal Quantum Number
Represented by n
Energy level occupied by the electron
Number of orbitals in the energy level = n2; number of electrons = 2n2
Angular Momentum Quantum Number
Represented by l
Shape of the orbital
Numbers 0 to 3 corresponding to s, p, d and f respectively.
Magnetic Quantum Number
Represented by m
Orientation of the orbital around the nucleus
-l to +l
Spin Number
Only 2 values +1/2, -1/2

15. Pauli Exclusion Principle
No two electrons can have the same set of four quantum numbers.
Therefore, no more than two electrons can occupy an orbital, and these two must have opposite spins

16. Aufbau Principle
An electron occupies the lowest energy orbital that can receive it.

17. Hund’s Rule
Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in a singly occupied orbital must have the same spin state.
The arrangement of electrons with the maximum number of unpaired electrons is the most stable arrangement.

18. Electron Configuration
The arrangement of electrons in an atom
Ground-State Electron Configuration – The lowest energy arrangement for each element
Hydrogen - 1s1
Helium – 1s2
Noble Gas Configuration
Lists the noble gas immediately preceding the element to represent the electron configuration of that noble gas
The electron configuration continues with the next orbital following the noble gas configuration
Be [He]2s1

19. Electron Configurations

20. Orbital Notation
Can use boxes or underlines