1. Electrons in Atoms
Chapter 5

2. Atomic Timeline

3. Models of the Atom
Rutherford’s atomic model could not explain the chemical and physical properties of elements
Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus
Each possible electron orbit has a fixed energy called energy levels
Quantum of energy is the amount of energy required to move an electron from one energy level to another energy level

4. Bohr Model
The energy level closest to the nucleus has the lowest energy
As you move away from the nucleus the energy increases
The amount of energy an electron gains or loses is not always the same
The energy levels of an atom are not evenly spaced
The higher energy levels are closer together
It takes less energy to move from one energy level
to another, the further away from the nucleus
Hydrogen

5. Quantum Mechanical Model
Electron cloud
Schrodinger
Determines the allowed energies an electron can have and how likely it is to find the electron in various locations around nucleus
Like the Bohr model, the quantum mechanical model DOES restrict the energy of electrons to certain values (Energy Levels)
The cloud is more dense where the
probability of finding the electron is high.

6. Atomic Orbitals
Region of space in which there is a high probability of finding an electron
Orbitals are found within each energy level
Energy levels are also called principal quantum numbers (n)
n=1, n=2, n=3, up to n=7
Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found
s orbital: spherical
p orbital: dumbbell-shaped
d orbital: clover leaf shape
f orbital: more complicated

8. Cross sections of atomic orbitals

9. Atomic Orbitals

10. Electron Configurations
How electrons are arranged in various orbitals around the nucleus of an atom
Three rules tell you how to find the electron configuration of atoms
Aufbau Principle
Pauli Exclusion Principle
Hund’s Rule

11. Aufbau Principle
Electrons occupy the orbitals of lowest energy first

12. Pauli Exclusion Principle
Atomic orbital can hold a maximum of 2 electrons
Electrons in one orbital must have opposite spins
Clockwise and counterclockwise

13. Hund’s Rule
Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible
Electrons DON’T double up until they have to

14. Electron Configuration Diagrams

15. Relate to Periodic Table
Period number on periodic table = the energy level
Exception: Transition metals (n-1)
Exception: Inner transition metals (n-2)
Elements can be sorted into noble gases, representative elements, transition metals, or inner transition metals based on their electron configurations.
Representative elements:
Groups 1A-7A

16. Orbital Blocks of Periodic Table

17. Electron Configurations

18. Exceptions Rule Breakers!
Half-filled sublevels are not as stable as filled sublevels, BUT are more stable than other configurations
Common examples: Copper and chromium
Rule Breakers!

19. Light Light behaves as a particle and as a wave
Amplitude: wave’s height
Wavelength: distance between crests
Frequency: number of wave cycles to pass a given point per unit time
Cycles/second = Hertz (Hz) or s-1
c = speed of light
c = 3.00 x 108 m/s

20. Waves

21. Electromagnetic radiation: radio waves, microwaves, infrared waves, visible light (roygbiv),ultraviolet waves, x rays, and gamma rays
All electromagnetic waves travel in a vacuum at a speed of X 108 m/s.

22. Atomic Emission spectrum
The frequencies of light emitted by an element separate into discrete lines to give the atomic emission spectrum of the element.
Fingerprint of the element

23. Explanation
In the Bohr model, the lone electron in the hydrogen atom can have only certain specific energies.
When the electron has its lowest possible energy, the atom is in its ground state.
Excitation of the electron by absorbing energy raises the atom from the ground state to an excited state.
A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level.
Light emitted is also called a photon.

24. Energy of electrons
The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.
E= h x v where h=6.626 x Js
E= hc/λ where c= x 108 m/s
c= v x λ

25. Hydrogen’s spectrum
The three groups of lines in the hydrogen spectrum correspond to the transition of electrons from higher energy levels to lower energy levels.
n=1 Lyman series
n=2 Balmer series
n=3 Paschen series

26. Quantum Mechanics
Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves.
All objects have wavelike behavior
The Heisenberg uncertainty principle states that it is impossible to know exactly both the velocity and the position of a particle at the same time.

27. Heisenberg Uncertainty Principle