1. Structure of the Atom
2. The Greeks (400 BCE)
a. 4 elements: air, earth, fire, water
b. Atoms made of elements in ratios
c. Differ in shape, position, arrangement
d. Can be rearranged to made new material
3. Lavoisier (1782)
a. Perfected quantitative method
b. First effective definition of element
c. Introduced logical nomenclature
d. First table of elements
e. Observed reactions in sealed containers
f. Total mass remained same
g. Conservation of matter:
i. Matter neither created or destroyed, just rearranged
4. Proust (1799)
a. Measured masses of elements in compounds
b. Always found same proportion by mass
c. Law of definite proportions
5. Dalton (1803)
a. Formed theory to explain results of Lavoisier, Proust, and others
b. All matter is made of atoms
c. Atoms of an element are unique
d. Key feature is atomic weight (mass)
e. Defined 1 amu as mass of H
f. Cannot be destroyed by chemical means
g. Did not recognize elements as molecules
h. Combine in simple ratios to make compounds
i. Can be broken apart and rearranged
6. Law of Multiple Proportions
a. Dalton formed from atomic theory
b. Same number of atoms present before and after
c. Ratio of atoms in a compound can be expressed in small whole numbers
7. Berzelius (1816)
a. Experimental verification of Dalton
b. First accurate table of atomic weights
c. Originated alphabetic symbols
8. Definitions
a. Hypothesis: a testable explanation or description based on observations (fact)
b. Theory: an explanation that has been tested
c. Law: a description that has been tested
9. Extension: Guy-Lussac (1808)
a. Experimentally developed and proved the law of multiple proportions for gases
10. Extension: Avogadro (1811)
a. Experimentally determined equal volumes of gases have same number of molecules (6.022 x 1023)
11. Discovery of Electron (e-)
12. Thompson
a. Experimented with cathode rays
b. Found rays were affected by magnetic and electric fields
c. Must be matter
d. Used force to determine charge to mass ratio (1.759 x1011 coulomb/gram)
13. Milikan
a. Found charge and mass of electron
b. Oil drop experiment:
i. Used electric charges to balance gravity
ii. Charge depended on mass of drop
iii. Always multiple of same value
iv. -1.6 x10-19 C
14. Milikan
a. Mass of electron
i. Divide charge by charge mass ration
ii. 9.10 x 10-31 kg
15. Discovery of Proton (p+)
16. Goldstein
a. Found positive rays coming from anode
b. Travel opposite direction as cathode rays
17. Thompson
a. Showed they were particles
b. Magnitude of charge same as e- but positive
c. Mass: 1.67 x 10-27kg (1836 times that of electron)
18. Atomic Model
a. Large positive sphere of protons
b. Embedded electrons
c. Same number of protons and electrons
19. Rutherford: Gold Foil Experiment
a. Shot alpha particles at foil
b. Expected all to pass through
c. Some bounced back
d. Should not have happened with large nucleus
20. New Model
a. Small positive nucleus
b. Electrons around the nucleus
c. Atom mostly empty space
21. The Neutron
a. Thompson discovers isotopes of Ne
b. Rutherford postulates a neutral particle with same mass as proton
c. Put in nucleus with proton
d. Discovered by Cavendish in 1930
22. Atomic Mass (A)
a. Number of mass units present
b. Roughly sum of protons and neutrons
c. Determined by mass spectrometer
23. Mass Spectrometer
a. Element converted to gas and given charge
b. Path of particle bent by magnetic field
c. Mass calculated from field strength, velocity and path
d. Weighted average in periodic table
24. Atomic Number (Z)
a. Number of protons
b. Counted by x-ray diffraction
c. Number of protons determines identity of element
d. Matches number of electrons
25. Where are the electrons
26. Problems with Model
a. Electrons do not spiral to nucleus
b. Atoms radiate in discrete steps
27. Spectrum Experiments
a. Elements emit only specific frequencies
b. White light passing through elemental gas loses specific frequencies
c. Frequencies emitted and absorbed are same
d. Spectrum serves as fingerprint
28. Max Planc: Background
a. Based theory on study of line spectra
b. Frequency of light related to temperaturen (KE)
c. Total amount of energy was finite
29. Max Plance: Quantum Theory
a. Electron could have only discrete units of enery
b. Units of energy called quanta
c. Energy related to frequency
i. E=nhf
ii. f = frequency
iii. h = 6.6 x 10-34J•s
iv. n = Principle quantum number
30. Nils Bohr
a. Emitted energy corresponds to change in electron energy
b. Absorbed or emitted in whole quanta
c. Orbit of electron determined by energy
d. Ground state: orbit of least energy
31. New Model
a. Small positive nucleus
b. Electrons orbit
c. Energy determines radius of orbit
d. Accurate only for H2
i. Number of particles complicates
32. Schrödinger et al
a. Wave equation: probable location
b. Uncertainty: unable to know p and x
c. Exclusion: each electron unique
33. Standard Model
a. Small positive nucleus
b. Electrons act as cloud
c. Energy level determines radius
d. Bohr radius most probable (bell curve)
34. Valence Electrons
a. Outer energy level
b. Involved in chemical reactions
35. Lewis Diagrams
a. Show only outer level electrons (s and p)
b. Symbol in middle
c. 1 dot for each outer electrons
d. Distribute evenly around symbol