1. ATOM Rich -Paradis Early Thoughts Aristotle-- Continuous theory
Matter can be divided indefinitely
Greeks
matter is made up of particles--4 elements
4 elements --air--fire--water--- earth
Democritus --Discontinuous theory
Matter can not be divided indefinitely
Atoms-indivisible
Rich -Paradis

2. Dalton’s Atomic Theory
ATOMIC THEORIES
Dalton’s Atomic Theory
• All elements are composed of individual atoms.
•All atoms of a given element are identical
• Atoms of different elements are different.
•Compounds are formed by the combination of atoms of different elements (Law of Definite Proportions)
Reactions are rearrangements of atoms
Sphere
Uniform density
Fire ball

3. Cathode Tube -cathode rays are a form of radiation that
contain an electrical charge
-rays move from negative to positive
-rays are negative (electrons)
Cathode ray
Negative
electrode
Positive
electrode

4. JJ Thomson’s Model
used the cathode ray tube to show one of the smaller units (particle) that make up the atom
Thomson theorized that an atom contains small negatively charged
particles electrons
His model is the “Plum Pudding”
Negative electrons float around
Bulk of the atom is positive
Still uniform density

5. Hypothesis Rutherford’s Gold Foil Experiment
Alpha emitter
(positvie charge)
screen
Gold foil
Hypothesis
Because the atom has uniform density, the alpha particles will pass straight through with little to no deflection.
Like a bullet through a stick of butter.

7. Results Conclusion Rutherford’s Gold Foil Experiment
The atom does not have uniform density.
*Because the alpha particles passed through, there must
be empty space.
*Because the alpha particles were bounced back, they must
have hit something dense.
*Because the alpha particles were deflected, the dense part
must have a positive charge.

8. Rutherford’s model Mostly empty or unoccupied space Dense positive
center
Electrons float around randomly in the empty space

9. Chadwicks -discovered the neutron
-when doing studies, he found that the atom often weighed twice as much as he anticipated with the number of protons
-he determined that there must be some other particle with the same mass as a proton but had no charge
-neutrons are located in the dense positive center (nucleus)

10. X Particle Symbol Charge Mass Location proton p + 1 nucleus neutron n
Subatomic
Particle
Symbol
Charge
Mass
Location
proton p
+ 1
1 amu
nucleus
neutron n
electron e
- 1
1/1836 mass of a proton
shell
nucleons
Protons
And
neutrons
Nuclear charge
# of Protons X A Z
Mass number = # of protons + #of neutrons
Atomic number =#of protons

11. K I-131 Se I Calculate the number of protons, neutrons, and electrons.39 19
I-131 Se 79 34
Mass #
Rewrite: I
131 53
P- N- E- 34
P- N- E- 19 45 20
P- N- E- 53 34 19 78
When an atom is neutral (no charge),
the number of electrons will equal the protons. 53

12. -has a charge (pos or neg)
Ion
-has a charge (pos or neg)
Gain electrons = negative ion
17Cl - 35 P- 17 N- 18 E- 18
Lose electrons = positive ion
20Ca2+ 40 P- 20 N- 20 E- 18

13. Isotope C 14 6
-Atoms with the same atomic number, but different mass number
-same bottom, different top
-differ in the number of neutrons C 12 6

14. Atomic Mass
-is the weighted average of all naturally occurring isotopes.
-based on the percent abundance and mass
1. Write percent as decimal.
2. Multiply decimal by the mass #.
3. Add them up.
4. Units will be atomic mass units
(amu)
75% Cl-35
25% Cl-37
.75 x 35 = 26.25
.25 x 37 = 9.25
35.50 amu

15. 2(n2) 2-8-8 1st level 3rd level 2nd level 1 2(12) 2 2 2(22) 8
•proposed a model of the atom showing a dense nucleus with electrons found in surrounding orbits.
•Bohr model shown shows a nucleus surrounded by electrons in circular orbits.
•Each electron must posses just the right amount of energy to keep it in
place around the nucleus.
energy levels
principal energy levels
shells
2(n2)
Energy level
Energy level Max # of e’s
(12) 2
(22) 8
the distribution of the electrons in an atom
(32) 18
2-8-8
(42) 32
1st
level
3rd
level
In theory
We will assume
only 32 per level
2nd
level
(52) 50
(62) 72
(72) 98

16. represents atom from the nucleus to the valance shell
are electrons in the outer energy level of
the atom
quantum-- a discrete amount of energy
-- each energy level represents a specific quanta
-- to move from one level to another, you must use that much energy
Excited state
when an electron
absorbs energy and
jumps to a higher level
can’t stay there
pattern skips 2-7-1
NOT on periodic table
WAS: 2-8 (moved 1 e- to the next level)
Ground state
all electrons are in the
lowest possible level
will follow the pattern:
2-8-18
Pattern on periodic table
Electrons can not stay excited, when electrons drop to a lower level, energy is released in the form of light(photon). Each element gives off a specific color and spectrum.

17. R O Y G B I V •each element gives off their own bright
continuous spectrum
bright line spectra
R O Y G B I V
•each element gives off their own bright
line spectrum
•each line represents an electron
dropping to a lower level
•fingerprint of an element
•white light through a prism or a
diffraction gradient
•shows all the colors in the visible spectrum
•diffraction gradient separates the light

18. Modern Theory -- Wave (Quantum) Mechanical Model
electron cloud
electrons don’t travel in fixed paths but are located in regions of space called orbitals
we don’t know the exact location of the electron but can guess where it is most likely located
based on probability