1. The Atom
Section Notes

2. Some videos… http://www.youtube.com/watch?v=caYxrueCHiQ
You might be giants - Elements

3. History of Atomic Models
Democritus (~400BC)
atomos = small, solid, indestructible particles of different shapes & sizes
These were just ideas, not truly science…
Dalton’s Atomic Theory
Billiard Ball Model - small solid sphere
Developed notion of conservation of mass and that atoms combine in specific ratios

4. History of Atomic Models
J.J. Thomson
Plum Pudding Model - positive and negative particles dispersed throughout the atom
Used Cathode Ray tubes to discover the electron - first subatomic particle discovered!

5. Cathode Ray Tube
A tube that contains a stream of electrons going from a negative disk (cathode) to a positive disk.
Deflected stream showed that electrons are negative.

6. Rutherford Nuclear Model
Discovered dense positively charged nucleus of the atom while working with alpha particles
Gold Foil Experiment

8. History of Atomic Models
Neils Bohr -
Also Solar System Model
Electrons travel in specific, circular orbits
Schrodinger & Heisenburg -
Quantum Mechanical Model
Dense nucleus w/ protons & neutrons
Electrons exist in ‘clouds’ called orbitals w/ specific energy levels
Mathematical predictions for probability of finding electrons
Electrons have particle and wave properties

9. What do you already know about atoms?
Brainstorm about what you already know (or are pretty sure of…) about atoms.
Write it down on your paper, then we’ll discuss.

10. How big is the nucleus?!?
Go to atoms videoclip

11. Comparing subatomic particles…

12. sToP & tHinK
If an atom has 2 protons and 2 neutrons, what is its atomic mass in atomic mass units (amu)?
What is the charge on an atom that has 7 protons and 7 electrons?

13. Atomic Number # of protons # of electrons in a NEUTRAL atom
Always a whole number

14. Mass Number # of protons + neutrons in atomic mass units (amu)
Isotopes - atoms of the same element with different masses
differ in number of neutrons
Examples: Carbon-13 & Carbon-14, Boron-10 & Boron-11
Element-mass#

17. Calculating # of neutrons
Subtract atomic # from mass #
Example:
Aluminum
13 protons
27-13 = 14 neutrons

18. sToP & tHinK What element has the atomic number 8?
How many protons, neutrons, and electrons are in a neutral atom of Potassium (K)?
How many protons, neutrons, and electrons are in a neutral atom of Boron-11?

19. Average Atomic Mass & Molar Mass
Average mass of all the atoms of a sample for an element
In amu’s for individual atom
In grams for a mole of that element = molar mass

20. Relative Abundance
The atomic mass on the PT is the average of the isotopes for that element.
Example: Lithium has two isotopes, one has a mass of 6 amu & one has a mass of 7 amu. Lithium-7 occurs 92.5% of the time…
Multiply the mass by the abundance
Add the two together to get the atomic mass for the element
What is Lithium’s average atomic mass?

21. sToP & tHinK
The published average atomic mass of phosphorus is If it has two isotopes, phosphorus-30 and phosphorus-31, which one is more abundant. Explain.

22. sToP & tHinK
An element has two isotopes. One has a mass of 24 amu and represents 70% of the atoms of the element, the other has a mass of 25 amu and represents 30% of the atoms of the element.
What is the average atomic mass?