1. Atomic Structure/ Periodic Table

2. The Structure of the Atom
In the beginning all that was known was that matter was made of something
Dalton: One part of his atomic theory named the small neutral particle that everything was made of an “atom”
It was represented as a sphere
J. J. Thomson used a cathode ray tube to prove that atoms could be made to release negative particles.

4. A New Atomic model
Rationale: If the atom contains negative particles and the entire atom is neutral then it must also contain something positive to counterbalance the electron charges…
The atom was therefore thought to be a positive mass with negative particles imbedded in it. The Plum Pudding Model

5. The Plum Pudding Model Equal # of protons and electrons
Overall charge is neutral
First to identify protons and electrons
JJ Thomson

6. Rutherford set out to test Thomson’s hypothesis
Alpha Particles are positively charged particles that are released from radioactive material (like uranium, plutonium, etc…)
Rutherford’s experiment was to shoot alpha particles at a piece of gold foil.
He thought that the alpha particles would go straight through and maybe occasionally be deflected a tiny bit by the positive mass of the atoms.

7. Rutherford’s Gold Foil Experiment

8. Rutherford was surprised!
Most of the particles went straight through, a few of them bounced back.

9. Rutherford proposed the nuclear model of the atom.
1. Atoms are mostly empty space.
2. Atoms have a small, massive nucleus.
3. The nucleus is positively charged.
4. Surrounding the nucleus are electrons, which have very little mass.
Note: Rutherford’s experiment does NOT say what the nucleus is made of or what the electrons are doing around the nucleus.

10. Bohr’s model: Orbits
Bohr realized that atoms could be made to emit light.
His explanation was that electrons are assigned to energy levels outside the nucleus
The electrons within these energy levels orbit at certain distinct distances from the nucleus.
In order to change it’s orbital pattern the electron must loss or gain energy. This happens in the form of light.

11. Bohr’s model

12. Bohr Atom & Light
Photon
The ground state of an electron is the lowest state of energy for that electron.
Photons contain radiant energy or “packets of light”.

13. Bohr Atom & Light
The excited state occurs when an electron absorbs the energy.
Electron jumps to a higher
energy level.
Electrons do not stay in the excited state for very long.

14. Bohr Atom & Light
The electron falls down to the ground state and emits energy in the form of light.

15. Atoms and Light
When an atom absorbs energy - in the form of heat, light- it re-emits that energy as light.
Every atom emits light in different colors (wavelength).

16. Continuous Spectrum

17. Emission Spectrum
If we separate the light by passing it through a prism, we can observe the atom’s emission spectrum.
No two elements have the same emission spectrum because the spacing of energy levels is different for each atom.

18. Spectroscopy Lab

19. Light measured… C = ν 
Speed of light (3 x 108 m/s) = frequency x wavelength
Hertz (Hz) or
Wave/sec
Meters

20. Energy E = h ν E: Enery in joules
h: Plank’s constant = x J*s
ν: Frequency

21. Electromagnetic Spectrum
Diagram showing the total range of electromagnetic radiation.
Energy (radiant energy) moves in waves.
Radio waves have lowest energy and lowest frequency.
Gamma waves have highest energy and highest frequency.

23. Light Equations Speed of light equation:
Speed of light = Frequency x Wavelength

24. Different Theories of the Atom
Model we will use
Current Model
90%probability

25. Atoms, Ions, and Isotopes
Made of electrons, protons, & neutrons
Smallest unit of an element
Neutral charge
Ion:
Atom that has lost or gained electrons
Has a + or - charge
Isotope:
Atoms of the same element that have differing numbers of neutrons

26. Isotopic Nomenclature
X = elemental symbol
A = Mass # (p + n)
Z = atomic # (p)

27. Isotopic Nomenclature Practice
Write the following in isotopic form:
Cl with 20 neutrons
C with 8 neutrons
How many neutrons do each of the following elements have?
2016S
1713Al

28. Isotopic Shorthand
C with 8 neutrons is
Cl with 20 neutrons is

29. Average Atomic Mass
The atomic mass is the weighted average of all isotopes of that element. |
A Weighted average reflects: 1) Mass (p + n) 2) Relative Abundance (%)
The mass on the periodic table is known as the average atomic mass.

30. Calculating Average Atomic Mass
If chlorine has 2 isotopes: Cl-37 at 20% and Cl-35 at 80%, then average atomic mass is