Atomic Structure Timeline

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Atomic Structure Timeline
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Democritus (400 B.C.)

• Proposed that matter was composed of tiny
  indivisible particles
• Not based on experimental data
• Greek atomos

3
Alchemy (next 2000 years)

• Mixture of science and mysticism.
• Lab procedures were developed, but alchemists did
  not perform controlled experiments like true
  scientists.

4
John Dalton (1807)

• British Schoolteacher
• based his theory on others experimental data
• Billiard Ball Model
• atom is a uniform, solid sphere

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John Dalton
Daltons Four Postulates
1. Elements are composed of small indivisible
particles called atoms. 2. Atoms of the same
element are identical. Atoms of different
elements are different. 3. Atoms of different
elements combine together in simple proportions
to create a compound. 4. In a chemical reaction,
atoms are rearranged, but not changed.
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Henri Becquerel (1896)

• Discovered radioactivity
• spontaneous emission of radiation from the
  nucleus
• Three types
• alpha (?) - positive
• beta (?) - negative
• gamma (?) - neutral

7
J. J. Thomson (1903)

• Cathode Ray Tube Experiments
• beam of negative particles
• Discovered Electrons
• negative particles within the atom
• Plum-pudding Model

8
J. J. Thomson (1903)

• Plum-pudding Model
• positive sphere (pudding) with negative
  electrons (plums) dispersed throughout

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Ernest Rutherford (1911)

• Gold Foil Experiment
• Discovered the nucleus
• dense, positive charge in the center of the atom
• Nuclear Model

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Gold Foil Experiment

• Alpha particles shot through gold foil. Most
  went straight through. A few were deflected
  because the particle hit the nucleus of the gold
  foil.

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Ernest Rutherford (1911)

• Nuclear Model
• dense, positive nucleus surrounded by negative
  electrons

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Niels Bohr (1913)

• Bright-Line Spectrum
• tried to explain presence of specific colors in
  hydrogens spectrum
• Energy Levels
• electrons can only exist in specific energy
  states
• Planetary Model

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Niels Bohr (1913)
Bright-line spectrum

• Planetary Model
• electrons move in circular orbits within specific
  energy levels

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Niels Bohr
Brightline spectrum
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Erwin Schrödinger (1926)

• Quantum mechanics
• electrons can only exist in specified energy
  states
• Electron cloud model
• orbital region around the nucleus where e- are
  likely to be found

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Erwin Schrödinger (1926)

• Electron Cloud Model (orbital)
• dots represent probability of finding an e- not
  actual electrons

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James Chadwick (1932)

• Discovered neutrons
• neutral particles in the nucleus of an atom
• Joliot-Curie Experiments
• based his theory on their experimental evidence

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James Chadwick (1932)

• Neutron Model
• revision of Rutherfords Nuclear Model

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Atomic Structure

• Structure of the Atom
• Chemical Symbols
• Subatomic Particles

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A. Chemical Symbols

• Capitals matter!
• Element symbols contain ONE capital letter
  followed by lowercase letter(s) if necessary.

Metal that forms bright blue solid compounds.
Co vs. CO
Poisonous gas.
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B. Subatomic Particles
ATOM
NUCLEUS
ELECTRONS
PROTONS
NEUTRONS
NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
Atomic Number equals the of...
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B. Subatomic Particles

• Quarks
• 6 types

• 3 quarks 1 proton or 1 neutron

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Ch. 10 - Atomic Structure

• II. Electron Cloud Model
• Orbital
• Energy Levels
• Bohr Model Diagrams

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A. Orbital

• Region where there is 90 probability of finding
  an electron.

• Cant pinpoint the location of an electron.
• Density of dots represents degree of probability.

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A. Orbital

• Orbitals have different shapes.

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B. Energy Levels

• Electrons can only exist at certain energy
  levels.
• Low energy levels are close to the nucleus.
• Each energy level (n) can hold 2n2 electrons.

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C. Bohr Model Diagrams

• Simplified energy levels using Bohrs idea of
  circular orbits.

Lithium Atomic 3 Mass 7 of
p 3 of e 3 of n 4
e-
e-
Maximum e- Level 1 2e- Level 2 8e- Level
3 18e- Level 4 32e-
e-
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Atomic Structure

• III. Masses of Atoms
• Atomic Mass
• Mass Number
• Isotopes

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A. Atomic Mass

• atomic mass unit (u or amu)
• 1 u 1/12 the mass of a 12C atom

• 1 proton 1 u 1 neutron 1 u
• 1 u 1.67 ? 10-24 g

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B. Mass Number

• Sum of the protons and neutrons in the nucleus of
  an atom.

• Always a whole number.

• of neutrons mass - atomic

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C. Isotopes

• Atoms of the same element with different numbers
  of neutrons.

• Isotope symbol

Carbon-12
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C. Isotopes
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C. Isotopes

• Average Atomic Mass
• reported on Periodic Table
• weighted average of all isotopes

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C. Isotopes

• EX About 8 out of 10 chlorine atoms are
  chlorine-35. Two out of 10 are chlorine-37.

35.4 u
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Ch. 10 - The Periodic Table

• I. History of the Periodic Table
• Mendeleev
• Mosely

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A. Dmitri Mendeleev

• Dmitri Mendeleev (1869, Russian)

• Organized elements by increasing atomic mass.
• Predicted the existence of undiscovered elements.

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B. Henry Mosely

• Henry Mosely (1913, British)

• Organized elements by increasing atomic number.
• Fixed problems in Mendeleevs arrangement.

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Ch. 10 - The Periodic Table

• II. Organization
• Metallic Character
• Rows Columns
• Table Sections

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A. Metallic Character

• Metals
• Nonmetals
• Metalloids

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B. Table Sections

• Representative Elements
• Transition Metals
• Inner Transition Metals

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B. Table Sections
Overall Configuration
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C. Columns Rows

• Group (Family)
• Period

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Ch. 10 - The Periodic Table

• III. Periodic Trends
• Terms
• Periodic Trends
• Dot Diagrams

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A. Terms

• Periodic Law

• Properties of elements repeat periodically when
  the elements are arranged by increasing atomic
  number.

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A. Terms

• Valence Electrons
• e- in the outermost energy level
• Atomic Radius

• First Ionization Energy
• energy required to remove an e- from a neutral
  atom

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B. Periodic Trends

• Atomic Radius

• Increases to the LEFT and DOWN.

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B. Periodic Trends

• First Ionization Energy

• Increases to the RIGHT and UP.

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B. Periodic Trends

• Which atom has the larger radius?

• Be or Ba
• Ca or Br

Ba Ca
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B. Periodic Trends

• Which atom has the higher 1st I.E.?

• N or Bi
• Ba or Ne

N Ne
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B. Periodic Trends

• Group of valence e- (except He)
• Families have similar reactivity.
• Period of energy levels

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C. Dot Diagrams

• Dots represent the valence e-.
• EX Sodium

• EX Chlorine