1. Arrangements of Electrons in Atoms
Chapter 4
Arrangements of Electrons in Atoms

2. Objectives
-Define the following terms: quantum, photon, photoelectric effect, frequency, wavelength
-Be able to explain the dual wave-particle nature of light
-Describe Bohr’s model of an atom

3. Structure of the Atom -Things we know:
Atoms are made up of 3 subatomic particles
The nucleus holds the _________ & _________
The electrons are located ____________
We know this thanks to Thomson (electron) Rutherford (proton & nucleus) , Chadwick (neutron)

4. Models of Atom -Thomson’s “Plum Pudding” model: -Rutherford’s Model:
Problem with model-
Didn’t explain exactly where electrons could be found in the atom

5. Properties of Light

6. Electromagnetic Spectrum
-the range containing all of the possible
frequencies and wavelengths of
electromagnetic radiation
Relationship between light and electrons
Research on light helped determine new model of atom
Light once thought of just as wave
Types of electromagnetic radiation

7. Electromagnetic Spectrum
In order of increasing wavelength: Gamma Rays, X-Rays, Ultraviolet Rays, Visible Rays, Infrared, Microwaves, Radio Waves
-Visible Light:
the light WE can see

8. Parts of a Wave

9. Dual Wave/Particle Theory
Waves have dual wave-particle properties.
Light can act as a wave or as a particle.

10. Properties of Light -Wave description of Light
- light exhibits wavelike behavior as it travels through space.
Wavelength (λ): distance between two peaks; unit of measure – meter, cm, nanometer
Frequency (f): number of waves that pass a given point in a specific time; unit of measure – Hertz (Hz)
Speed of light (c ): c= λf c=3.00 X 108 m/s

11. Wave Description of Light
Calculate the wavelength if the frequency of radiation is 5.10x1014Hz.

12. Properties of Light Particle description of light:
light can be thought of as being composed of particles (Planck)
Photon: particle of light. Has zero mass and a quantum of energy (Einstein)
Quantum: minimum quantity of energy that can be lost or gained by an atom

13. Photoelectric effect
Photoelectric effect- refers to the emission of electrons from a metal when a light of sufficient energy shines on the metal
Wave theory of light couldn’t explain this effect
With high energy and low wavelength electrons are ejected

14. Properties of Light
Therefore, light has dual wave- particle properties
- It behaves like a wave AND a particle

15. E = hf
E - energy in Joules of a quantum of energy h - Planck’s constant = x J·s f – frequency (Hz)

16. Problems
Find the energy in a quantum of light that has a frequency of 1.7 x 1014 Hz

17. Light Equations Practice
1. Find the wavelength of a photon of light with an energy of 3.26 x J. 2. Hydrogen has a red emission line at 656.3nm. What is the energy and frequency of a photon of this light?

18. H atom Line-Emission Spectra
When you pass a current through a gas, at low pressure, the energy of some of the gas atoms increases.
Ground State - lowest energy state for an atom.
Excited state - An atom that has a higher potential energy

19. The Two Different Sides of the Spectrum
Prism
Screen
Slit
White light source
Gas discharge tube
CONTINUOUS SPECTRUM
FROM WHITE LIGHT SOURCE
VARIOUS COLORS BLENDED TOGETHER
DISCONTINUOUS SPECTRA
FROM EXCITED ATOMS
DISTINCT SEPARATED, ONLY A FEW COLORS

20. 2

21. If an electron in the n = 1 level of an H atom absorbs enough energy to move to the n = 4 level. How much energy is absorbed? n 4
If an electron in the n = 4 level of an H moves to the n = 2 level. How much energy is emitted? 3 2
Light of what wavelength is emitted in
a transition from n = 4 to n = 2?
Energy 1

22. Rydberg Formula E = 2.178x10-18(1/n2)
Or if there is a change in energy levels:
ΔE = 2.178x10-18(1/n2f – 1/n2i)
Ex. 1
What wavelength, in nanometers, is predicted by the Rydberg equation when an electron drops from the n=6 to the n=2 state?

23. Rydberg Formula
Ex. 2 What is the minimum wavelength of light that is capable of removing an electron from the 4th energy level of a hydrogen atom?

24. “Neon Lights”

25. Electron -Is a particle & also has wave properties
-Bohr’s Model of Atom:
-Electrons circle around
nucleus in allowed paths (orbits)
-Electrons placed in different
orbits based on energy levels of the electron
-One electron can not be in two orbits at once and can not be between orbits
*** Bohr’s model still has shortcomings… we will discuss later)

26. Take Home Message -Science is CONSTANTLY changing
-New research may disprove old findings
-New models and thoughts may be created as a result

27. Review 1) Name the two properties that light has.
2) What is the type of light that we can see called?
3) Visible light is found on the _________ spectrum.
4) A particle of light that has zero mass and a quantum of energy is called a ________.
5) The distance between two peaks is called_____
6) Name the model of an atom that said electrons circle around nucleus in allowed paths based on energy level.
7) The number of waves that pass a given point in a specific time is called ________
8) The minimum quantity of energy that can be lost or gained by an atom is a____________.
9) The ______________ refers to the emission of electrons from a metal when a light of sufficient energy shines on the metal

28. Electron -Is a particle & also has wave properties
-Bohr’s Model of Atom:
-Electrons circle around
nucleus in allowed paths (orbits)
-Electrons placed in different
orbits based on energy levels of the electron
-One electron can not be in two orbits at once and can not be between orbits
*** Bohr’s model still has shortcomings… we will discuss later)

29. Electron “Detection”
Electrons are detected with interaction with photons
Photons can knock an electron off its course
Heisenberg Uncertainty Principle:
It is impossible to determine simultaneously both the position and velocity of an electron or any other particle

30. Quantum Model - Schrödinger: wave equation Quantum Theory:
Electrons can exist in atoms only at specific energy levels
Wave equations only tell us probability of finding electron in certain position
Currently it is believed:
Electrons do not travel in orbits, but orbitals
Orbital: 3-D region around nucleus. Indicates probable location of finding an electron

31. Section 1&2 Review What properties do light and electrons share?
The emission of electrons from a metal when a light of sufficient energy shines on the metal refers to the ____________ effect.
The minimum quantity of energy that can be lost or gained by an atom is called______.
How is Bohr’s model different from the Quantum model of an atom?
What is the principle called that says it is impossible to determine simultaneously both the position and velocity of an electron or any other particle?
How is an orbital different from an orbit?
Which has a higher energy level, n=1 or n=5?

32. Objectives
-List the total number of electrons needed to fully occupy each main energy level
-State the Aufbau principle, Pauli exclusion principle, and Hund’s Rule
-Draw the electron configuration and orbital notation to show the location of electrons in an atom.

33. Electron Configuration
- Electron configuration: the arrangement of electrons in an atom
Rules for electron filling of orbitals:
Aufbau Principle: e- will occupy the lowest energy level orbital available
Pauli Exclusion Principle: no two e- in the same orbital can have the same spin
Hund’s Rule: orbitals of equal energy will fill singularly before a second e- can occupy the same orbital

36. Electron Configuration
Electron configuration shows the energy level number, the orbital sublevel, and the number of electrons in each orbital
# of e- are represented by a superscript
e- config for carbon:
1s22s22p2
Energy
level
Number of
electrons
Orbital
sublevel

37. Electron Config Practice
1. Write the e-config for fluorine.
1s22s22p5
2. Write the e-config for potassium.
1s22s22p63s23p64s1
3. Write the e-config for nickel.
1s22s22p63s23p64s23d8

38. Review
What rule says orbitals of equal energy will fill singly before a second e- can occupy the same orbital?
What rule says that e- will occupy the lowest energy level orbital available?
What rule says that no two e- in the same orbital can have the same spin?

39. Orbital Notation - Orbital notation shows e- in their orbitals
First write the electron configuration
Lithium
1s s1
Arrows must be up and down on each line – represents electrons with opposite spins –Pauli Exclusion Principle
Remember Hund’s Rule

40. Orbital Notation -Draw the orbital notation for aluminum.
-Draw the orbital notation for phosphorus

41. Objectives Write the noble-gas notation of a given element
Determine the element given the electron configuration or orbital notation.
Determine the highest energy level that is occupied and the last orbital that is filled of a given element.

42. Noble Gases Gases like helium, neon, and argon
Where are these on the periodic table?
Group 18
The outer shell is completely filled with 8 electrons
We can use their electron configuration to abbreviate the e- config. of other elements

43. Noble Gas Configuration
The electron configuration of Manganese is:
1s22s22p63s23p64s23d5
Manganese is in period 4…. What is the noble gas in the previous period? (period 3)---
Argon
Argon’s e- config. is:
1s22s22p63s23p6
We can shorten the e- config of Mn by writing:
[Ar] 4s23d5

44. Practice
- Write the Noble Gas Configuration of Na, Sr, and P

45. Identify the following elements
1s22s22p63s23p3
[Ar]4s1
1s22s22p1
[Ne]3s2

46. Review
What is the last orbital occupied by an electron in the elements: He Al
What is the highest energy level occupied by the following elements: Ca Be