history & development of atomic theory...history of atomic theory cathode ray tube electricity...
TRANSCRIPT
GC History of the Atom Notes.notebook
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October 21, 2011
Aug 2810:34 AM
History & Development of Atomic Theory
Aug 201:35 PM
History of Atomic Theory
The Alchemists ~ 300 BC to 300 AD
Experiment:
Beliefs:
Pseudoscience influenced by Aristotle,concerned with...
Using chemistry to change cheap metal to gold.Finding an eternal life elixir.
• All matter was made up of a combination of four elements; fire, air, earth, water
Aristotle
GC History of the Atom Notes.notebook
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October 21, 2011
Aug 201:58 PM
Experiment:
History of Atomic Theory
Dalton ~ early 1803 English School Teacher
Studied chemical reactions, recorded his observations and took measurements. From his results he developed the following theory...
John Dalton
Developed the first "official" atomic theory.
Aug 231:23 PM
Five Principles-Dalton's Atomic Theory
1. All matter is made of indestructible atoms.2. Atoms of the same element are identical in their physical and chemical properties.3. Atoms of different elements have different physical and chemical properties.4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.5. In chemical reactions, atoms cannot be subdivided, created, or destroyed. They are combined, separated, or rearranged.
Atomic Model: Sphere-Billiard Balls
Which principles remain true today?
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October 21, 2011
Aug 203:07 PM
Experiment:
Discoveries:
Model:
J.J. Thomson ~ 1897 English Physicist
History of Atomic Theory
Cathode Ray TubeElectricity is passed through a glass tube filled with gas. The gas beam can be bent with a magnet.
• Atoms consist of charged particles• The negatively charged particles are called electrons (1897)• The positively charged particles are called protons (1920)
Plum Pudding or Chocolate Chip CookiesJoseph John Thom
son
The chocolate chips represent negatively charged electrons stuck in positively charged dough.
Aug 203:19 PM
History of Atomic Theory
Experiment:
Model:
Discoveries:
Rutherford ~ 1911 English Physicist (a student of Thomson)
Gold Foil Experiment
Positively charged alpha particles are shot at a piece of thin gold foil. Most alpha particles had little deflection. Some were deflected at large angles.
• A positively charged core of an atom called the nucleus• Electrons surround the nucleus• The rest of the atom is empty space
Nuclear atom
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October 21, 2011
Aug 203:30 PM
History of Atomic Theory
Discoveries:
Model:
James Chadwick ~ 1932 English Physicist (Student of Rutherford)
• The nucleus contains another particle with no charge (neutral) and a mass equal to that of a proton.• Called this particle the neutron.
Sir James Chadwick
Same as Rutherford
Sep 167:33 AM
Rutherford's Model Revisted
The Nuclear Atom:• Atoms have a positively charged nucleus containing protons (+) and neutrons (0). Electrons (-) are located outside of the nucleus.
The Problem:According to the laws of physics, with nothing holding the electrons in place, the negatively charged particles would spiral into the positively charged nucleus (- and + charges attract) and Rutherford's atom would collapse.
GC History of the Atom Notes.notebook
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October 21, 2011
Sep 167:45 AM
Niels Bohr ~ 1913 Danish Physicist • student of both Thomson & Rutherford
He studied the light spectrum of hydrogen gas in an attempt to more accurately explain the role of electrons in the atom.
The Experiment:
Sep 167:29 AM
Also known as... electromagnetic radiation:What Is Light?
• form of energy• produced by electrically charged particles (like electrons!)• exhibits wave like behavior
Wavelength - the distance from one peak to another
Frequency - the number ofwaves that pass a particularpoint per second
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October 21, 2011
Sep 167:31 AM
The Electromagnetic Spectrum
Low Energy Light = longer wavelength & lower frequency red light = low energy light
High Energy Light = shorter wavelength & higher frequencyblue light = high energy light
Sep 167:59 AM
Light Spectrums
Hydrogen Spectrum
Helium Spectrum
• Bohr observed when energy (light or heat) was added to a sample of hydrogen gas a distinctive color was given off.• When he looked at the light through a prism, only certain color lines could be seen, instead of the whole rainbow like he expected.•
Hydrogen Spectrum
Helium Spectrum
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October 21, 2011
Sep 167:27 AM
Bohr's Atomic Model• Thought the atom contained energy levels which kept the electrons from falling into the nucleus.• Individual elements each have a unique arrangement of electrons in those energy levels. • When an atom absorbs energy the electrons enter into an "excited state" by jumping up to higher energy levels.• The excited state is unstable, so the electrons release the excess energy in the form of colored light.
• The color of the light observed is determined by the amount of energy released by the electrons.
Sep 169:41 AM
Important Vocabulary:
ground state-
excited state-
all electrons in their lowest possible energy levels
electrons absorbed energy & jump to a higher energy level
GC History of the Atom Notes.notebook
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October 21, 2011
Sep 167:59 AM
Bohr's Model: Solar System Electrons "orbit" around the nucleus in certain paths (energy levels).
Similar to the way the planets in our solar system orbit around the sun.The energy levels prevent the electrons from falling into the nucleus.
Sep 169:50 AM
The Problem with Bohr's Model???
It worked well for hydrogen, but not for elements containing more than 1 electron.
GC History of the Atom Notes.notebook
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October 21, 2011
Aug 204:21 PM
History of Atomic Theory
Experiment:
Discoveries:
Quantum Mechanics
Scientisits: Schrodinger & Heisenberg
NONE! Model is based on a mathematical calculation ONLY!
Erwin Schrodinger
• Mathematical model that deals with the probability of finding an electron within a given space around the nucleus. • These probability maps are called orbitals (or electron clouds)• There are four orbitals with different shapes: s p d f• These orbitals can be related to the periodic table
Aug 258:00 PM
Orbital Shapes
s - orbitals are spherical p - orbitals are dumbbell shaped
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October 21, 2011
Sep 76:48 PM
Orbital Shapes
d-orbitals are clover shaped f-orbitals
Sep 107:54 PM
Electron Configurations:
The Rules:
1. Aufbau Principle: An electron will occupy the lowest possible energy level.
2. Pauli Exculsion Principle: Each orbital cannot contain more than two electrons, and those electrons must have opposite spin.
3. Hund's Rule: Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all single electrons must have the same spin
Represent the arrangement of electrons in an atom.
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October 21, 2011
Sep 108:32 PM
Aug 234:09 PM
Using the Periodic Table to Write Configurations.
• Each row on the periodic table represents an energy level.
• The s, p, d and f-orbitals are represented by different "blocks" on the periodic table.
• The d-orbitals are located 1 energy level lower than the s & p orbitals in the same row.
• The electrons configuration for a particular element is determined by the location of that element on the table.
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October 21, 2011
Aug 234:16 PM
Examples...
HC
MgFe
AgBr
superscript = number of electrons in that orbital(# of spaces over on table)
Hydrogen:1s1
coefficient = energy level(row on periodic table) letter = orbital type
(periodic table block)
Configurations of Ions: Add or remove the number of electrons gained or lost to the end of the configuration.
Examples:Mg:Mg+2:
N:N-3:
NeS
HC
MgFe
AgBr
Aug 234:42 PM
Final Few Notes on Configurations:• Most ions have electron configurations identical to a noble gas. • Noble gases are stable. Therefore when ions form they lose or gain electrons in order to have stable electron configurations as well.
• Valence electrons - electrons in the highest energy level of an atom.Example: How many valence electrons does phosphorus have?
Examples: Mg:Mg+2:
S:S-2:
Compare to Neon's Configuration:1s22s22p6
1s22s22p6
Compare to Argon's Configuration: 1s22s22p63s23p6
1s22s22p63s23p6
1s22s22p63s2
1s22s22p63s23p4