1. Arrangement of Electrons in Atoms
Chapter IV

2. Properties of light Electromagnetic radiation Electromagnetic spectrum
A form of energy that exhibits wavelike behavior as it travels through space.
Electromagnetic spectrum
All the forms of electromagnetic radiation
X-rays, ultraviolet, infrared light, visible light, microwaves, and radio waves
Wavelength (λ)
Is the distance between corresponding points on adjacent waves.

3. Cont….
Frequency (v)
The number of waves that pass a given point in a specific time, usually one second.
Expressed waves/second
One wave/second is called a hertz (Hz)
Named for Heinrich Hertz
Frequency and wavelength have a mathematical function
C=λv

4. The photoelectric effect
The emission of electrons from a metal when light shines on the metal
Explained by Max Planck
Said light emits energy in small, specific amounts called quanta.
A quantum
The minimum quantity of energy that can be lost or gained by an atom

5. Math….
Plank proposed the relationship between quantum and frequency of radiation
E=hv
E is the energy in joules
V is the frequency of the radiation emitted
h is a fundamental physical constant
Known as Plank’s constant
h=6.626x 10 −34 J*s

6. Einstein
Albert Einstein expanded on Planck's theory by saying light acts like a particle and a wave.
Photon
A particle of electromagnetic radiation having zero mass and carrying a quantum of energy.
Ephoton=hv
Electromagnetic radiation absorbed by matter in whole numbers
Single photon possessing at least the minimum energy required to knock the electron loose must strike the material.
Energy is equal to frequency
So electrons in different metals require different minimum frequencies to exhibit photoelectric effect.

7. The Hydrogen-Atom Line-Emission Spectrum
When current is passed through a gas at low pressure, the potential energy of some of the gas atoms increase.
Some of this energy is given off as visible light
This is what makes neon lights glow
Ground state
Lowest energy state of an atom
EXCITED STATE
A state in which an atom has a higher potential energy than it has in its ground state

8. Cont…
When a current is passed through a vacuum tube with hydrogen gas at low temp it emits a pinkish glow.
When that light is then focused through a prism, it separated into a series of specific frequencies of visible light. This is hydrogen’s line-emission spectrum
Scientists expected to see a continuous spectrum so this result needed to be explained.
This explanation is a new theory of the atom called quantum theory.

9. Bohr Model
Niels Bohr proposed a model of the hydrogen atom that linked the atom's electron with photon emission.
According to this model electrons fell into orbits
Orbits are fixed energy levels that circle the nucleus.
The electron in the hydrogen atom must then occupy the space nearest the nucleus.
Lots of empty space between the orbits.
Higher the electrons energy the farther from the nucleus the orbital it resides in is.
So what Bohr says is that when an electron is excited it is in a higher orbit and wants to return to the lowest orbit. To do this it must release energy, in this case light.
Bohr used math to show his ideas fit with the observed lines.
End 4-1

10. The Quantum Model of the Atom
Since light behaves as both particle and wave the idea was proposed that an electron could act this way as well.
De Broglie pointed out that in many ways the behavior if Bohr’s quantized electron orbits was similar to the know behavior of waves.
So he proposed electrons act like wave in the orbits.
He was confirmed by experiments
Diffraction is when light bends as it passes though an object (think of the bent straw in a glass of water)
Interference occurs when waves overlap.
Both of these affects were seen when using beams of electrons.

11. The Heisenberg Uncertainty principle
The idea of electrons having dual wave-particle nature troubled scientists.
If both then where are they?
Hiesenberg came up with the idea to detect electrons by bumping them with photos of light. But the photon knocks the electron off course.
The Heisenberg uncertainty principle
It is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

12. Schrodinger wave equation
Assumed light acted like a wave.
Only waves of specific energies, and therefore frequencies, provided solutions to the equations.
Together with the Heisenburg uncertainty principle the foundation was laid for the modern quantum theory
Quantum theory
Describes mathematically the wave properties of electrons and other very small particles.
Replaced obits with orbitals
An orbital
A three-dimensional region around the nucleus that indicates the probable location of an electron.

13. Orbitals and Quantum numbers
A quantum number specify the properties of atomic orbitals and the properties of electrons.
Easy way to describe electrons
Quantum numbers
Principal quantum describes the energy level of the electron
Angular momentum quantum number
Describes the shape of an orbital

14. CONT Magnetic quantum number Spin quantum number
Symbolized by m indicates the orientation of an orbital around the nucleus
Spin quantum number
Two values
+1/2
-1/2
Ways the electrons spin.
End 4-2

15. Electron principles Aufbau principle Pauli exclusion principle
Electrons occupies the lowest-energy level that can receive it.
Pauli exclusion principle
No two electrons in the same atom can have the same set of four quantum numbers
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 singly occupied orbitals must have the same spin.

16. Elements of the second period
There are two orbitals in the second period
2s and 2p
The highest occupied level is the electron-containing main energy level with the highest principal quantum number
Inner-shell electrons
Electrons that are not in the highest occupied energy level.

17. Elements of the 3rd period
Now we can use noble gas notation
Sulfur
[Ne] 3s2 3p4

18. Elements of the 4th and 5th
Now have the d orbitals
Represents the metals
Has one lower orbital number

19. 6th and 7th Now we have an f orbital
Two quantum numbers lower than the period
Represents the lanthanides and actinides