Upload
byron-hunt
View
220
Download
3
Embed Size (px)
Citation preview
2
History of Atomic Theory
Democritus (from about 440 BC)coined the term atom which means uncuttableHe felt that if you kept cutting matter smaller and
smaller eventually you will no longer be able to cut any further.
2
3
John Dalton (1766-1844)3
Felt that an atom was indivisiblespherical in shapeModel: SphereAnalogy: Billiard ball
Dalton’s Postulates
Atoms are tiny, indivisible particles.Atoms of the same element are identical.Atoms of different elements can chemically
combine.Chemical reactions occur when atoms are
separated, joined or rearranged. Atoms of one element can never be changed to
atoms of another element.
4
Size of an atom
Pure copper coin the size of a penny = 2.4X1022 atoms
Earth’s population is about 6 X 109 people
5
6
JJ Thomson (1856-1940)
Discovered electronsFelt that an atom was negatively charged
particles floating in a positive soupModel: Charges floating aroundAnalogy: Raisin bun or Plum Pudding
6
77
Ernest Rutherford (1871-1937)
Discovered the nucleus, the proton and first split an atom
Model: An atom was a small positively charged nucleus surrounded by electrons orbiting around it.
Analogy: A beehive
88
Rutherfords Famous Experiment
Called the Gold Foil Experiment Alpha particles were fired at thin gold foil A detector encircled the foil and lit up when hit with
alpha particles. If the plum pudding model were true it was expected
most particles would go straight through the foil with only slight deflection.
However, in the experiment, some particles were deflected back at a sharp angle proving the existence of a small, dense, and positively charged nucleus.
9
Text
Plum pudding expected results. Particles go through.
Actual results. Some are deflected back due to a nucleus
Rutherfords results
1111
Niels Bohr
Worked out details of atomic structure. Notably orbital layers. Solved problems related to Rutherfords model.
Model: Electrons orbit in rings at different distances from the nucleus.
Analogy: Planets orbiting the sun
1212
Erwin Schroedinger (1887-1961)
Major discoveries in quantum mechanics. Nature of electrons in atoms.
Model: Electrons exist in a probability distribution around the atom. Kind of like a cloud.
Analogy: A spinning fan blade.
13
Quick Quiz: Historical Atom
1. What did Dalton say an atom was like?
2. What did JJ Thomson say an atom was like?
3. What did Rutherford say an atom was like?
4. What are the 3 parts of an atom?
1. A billiard ball, or a pool table ball
2. Raisin bun
3. A beehive
4. Proton, Neutron, Electron
13
15
Parts of the Atom15
The Nucleus
ElectronsMass=0Charge=-1
ProtonsMass=1Charge=+1
NeutronsMass=1Charge=0
Atomic Structure
An atom is considered electrically neutral.
Electrically neutral means the number of protons (+) = the number of electrons (-)
4 red protons4 red protons = = 4 blue electrons4 blue electrons
You must know how to find:A. # of protons = atomic number
B. mass # = # of n0 + # of p+ (atomic #) What’s in the nucleus of the atom
C. # of electrons = # of protons (in a neutral atom)
Boron
5
B10.811
atomic number
atomic mass(Not the same as the mass #)
Nuclear Symbol
16. What is the mass number?
The mass of the entire atom!The sum of the protons and neutrons in an atom.Electrons are not included (too small)
17. What is the atomic mass?
The weighted average of the masses of all naturally occurring isotopes.
How to write a Nuclear Symbol
B11
5
Mass Number
= p+ + n0
Atomic Number
= p+
-3
Charge if ionElement Symbol
22
To Determine Other Numbers 22
To find Do this
Proton # same as atomic number
Electron #same as atomic number for
neutral atoms
Neutron # =atomic mass-atomic number
Mass =Prot # + Neut#
Mg12
27 +2
Nuclear Symbol Examples
Atomic Number Mass NumberNumber of
ProtonsNumber of Neutrons
Number of Electrons
12 1227 15 10
Cl17
35
Atomic Number Mass NumberNumber of
ProtonsNumber of Neutrons
Number of Electrons
17 1735 18 17
+2
Nuclear Symbol Examples
Ca20
40
Atomic Number Mass NumberNumber of
ProtonsNumber of Neutrons
Number of Electrons
20 2040 20 18
O8
17 -2
Atomic Number Mass NumberNumber of
ProtonsNumber of Neutrons
Number of Electrons
8 817 9 10
Ions - an atom that has lost or gained an electron(s)
The charge on an ion indicates an imbalance between protons and electrons.
If the atom GAINS electrons it will have a negativenegative charge. (more e- than p+)
If the atom LOSES electrons it will have a positivepositive charge. (more p+ than e-)
BProtons = Electrons =
B+2
Protons =
Electrons =
5
11
5
11
Isotopes are atoms of the same element that have the same # p+, but different mass numbers.
Isotopes have different masses because they have a different number of neutrons.
Boron
5B10.811
atomic number
(average) atomic mass
Isotopes
19. How are isotopes written?
The element name with its mass number after it:Carbon-12Carbon-13Carbon-14
Learning Check
Naturally occurring carbon consists of three isotopes, C-12, C-13, and C-14. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C 13C 14C 6 6 6
# p _______ _______ _______
#n _______ _______ _______
#e _______ _______ _______ #