Atoms and Moles

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Chapter 3

• Atoms and Moles

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Atomic Models
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3.1 Matter Made of Atoms

• Atomic Theory
• Mikhail Lomonosov (1711-1795) and Antoine
  Lavosier (1743-1794) developed law of
  conservation of mass
• states that mass of reactants equals mass of
  products

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Law of Conservation of Mass
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Law of Conservation of Mass
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3.1 Matter Made of Atoms

• Atomic Theory
• Joseph Proust (1754-1826) proposed law of
  definite proportions
• states that two samples of a given compound are
  made of the same elements in exactly the same
  proportions by mass

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3.1 Matter Made of Atoms

• Atomic Theory
• Claude-Louise Berthollet (1748-1822) proposed
  law of multiple proportions
• states that when two elements combine to form two
  or more compounds, the mass of one element that
  combines with a mass of the other is in the ratio
  of small whole s

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3.1 Matter Made of Atoms

• Daltons Atomic Theory
• John Dalton (1766-1844) developed a new atomic
  theory
• 1. all matter is made of atoms, which cannot be
  subdivided, created, or destroyed
• 2. atoms of a given element are identical in
  their chemical and physical properties

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3.1 Matter Made of Atoms

• Daltons Atomic Theory
• 3. atoms of different elements differ in their
  physical and chemical properties
• 4. atoms of different elements combine in simple,
  whole-number ratios to form compounds

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3.1 Matter Made of Atoms

• Daltons Atomic Theory
• 5. in chemical reactions, atoms are combined,
  separated, or rearranged but not created,
  destroyed, or changed

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3.1 Matter Made of Atoms

• Further Progress
• Jons Berzelius (1779-1848)
• studied proportions in which elements combine
  with one another (over 2000)
• experimental underpinning of Daltons theory
• made table of atomic weights
• named halogens

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3.1 Matter Made of Atoms

• Further Progress
• Jons Berzelius (1779-1848)
• invented alphabetical nomenclature of elements
• coined terms organic chemistry, catalysis,
  and protein

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3.1 Matter Made of Atoms

• Further Progress
• valency and bonding described in 1850s
• Stanislao Cannizzaro (remember?) distinction
  between atoms and molecules
• periodic table developed in 1860s

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3.2 Structure of Atoms

• Subatomic Particles
• Heinrich Geissler (1814-1879) invented the
  vacuum tube (late 1850s)
• vacuum tube hollow, glass tube in which the air
  has been removed electrodes at either end
• produces a glow when current flows between
  electrodes

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3.2 Structure of Atoms

• Subatomic Particles
• Eugen Goldstein (1850-1930)
• named glowing rays cathode rays (1876)
• showed that they were deflected by magnetic
  fields could cast shadows
• discovered rays coming from anode called them
  canal rays (1886)

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3.2 Structure of Atoms

• Subatomic Particles
• William Crookes (1832-1919)
• showed that cathode rays were made of particles,
  not light (1879)
• convincing to the British, but not mainlanders

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3.2 Structure of Atoms

• Subatomic Particles
• J. J. Thomson (1856-1940) showed that rays were
  slower than light (1894)
• Jean Perrin (1870-1942) showed that metal plates
  hit by rays became negatively charged (1895)

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Three Random Walks
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3.2 Structure of Atoms

• Subatomic Particles
• J. J. Thomson (again)
• measured mass/charge found that particles were
  small or charge was large (1897)
• measured electric charge itself found electrons
  to be 1/2000 mass of a H atom (1899)
• new atomic model

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Deflections of Cathode Rays
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Thomsons Atomic Model
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3.2 Structure of Atoms

• Subatomic Particles
• Ernest Rutherford (1871-1937)
• discovered ? and ? radiation (1890s)
• discovered ? radiation (1900)
• discovered that ? particles are a He nucleus
  (1908)

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?, ?, ? Radiation
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? Radiation Image
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3.2 Structure of Atoms

• Subatomic Particles
• Ernest Rutherford (1871-1937)
• gold foil experiment (1909)
• ? particles fired at gold foil
• most went through, some deflected
• conclusion most of the mass and charge of an
  atom is in the nucleus electrons in cloud

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Gold
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Gold Foil Experiment
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Expectations versus Reality
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Explanation
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Explanation
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Rutherfords Paper
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3.2 Structure of Atoms

• Subatomic Particles
• Francis Aston (1877-1945) showed that atoms come
  in different varieties (different weights) (1912)
• called isotopes atoms with the same number of
  protons but different numbers of neutrons
• E.R. discovered proton (1918)

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Evidence for Isotopes
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3.2 Structure of Atoms

• Subatomic Particles
• James Chadwick (1891-1974) discovered the
  neutron (sort of) (1932)

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3.3 Electron Configuration

• Electrons and Light
• Light as a moving wave
• c ?f
• c ? speed of light 3 x 108 m/s
• ? ? wavelength (m) ? distance between peak or
  troughs of a wave
• f ? frequency (1/s ? 1 hertz) ? of waves per
  second

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Waves
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Light Waves
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Light
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3.3 Electron Configuration

• Electrons and Light
• Albert Einstein (1879-1955)
• atoms emit or absorb EM radiation in discrete
  (quantized) units (1905)
• light has properties of waves and particles (1905)

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3.3 Electron Configuration

• Electrons and Light
• Niels Bohr (1885-1962)
• worked with Rutherford
• new atomic model electrons orbit nucleus at
  particular energy levels (1912)
• electrons dont give off energy (no spiraling
  allowed)
• Why dont electrons go straight to the nucleus???

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3.3 Electron Configuration

• Electrons and Light
• Bohrs model
• electron in state of lowest possible energy is in
  ground state
• if electron gains energy, it moves to an excited
  state(!)
• if electron falls back to ground state, it
  releases energy as light

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Excited State
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Absorbance and Emission
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Absorbance and Emission
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Quantization
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3.3 Electron Configuration

• Electrons and Light
• Bohrs model, continued
• Bohr predicted the wavelengths of light for
  hydrogenhe was right!
• all light wavelengths together are called
  line-emission spectrum
• each element has its own

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Hydrogen Emission
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H Absorbance and Emission
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3.3 Electron Configuration

• Electrons and Light
• Louis de Broglie (1892-1987)
• particles can be described as waves (1925)
• therefore, electrons can only have certain
  frequencies (energy levels) and cant fall toward
  nucleus
• quantum atomic model

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3.3 Electron Configuration

• Quantum numbers
• n ? principal (main energy levels)
• l ? angular momentum (shape or type of sublevel)
• l 0 ? s orbital
• l 1 ? p orbital
• l 2 ? d orbital
• l 3 ? f orbital

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Principal Quantum Number
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Energy Level Transitions
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3.3 Electron Configuration

• Quantum numbers
• ml ? magnetic (subset of l quantum number)
• ms ? spin (orientation of magnetic field) 1/2 or
  -1/2

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Quantum Numbers
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Orbital Shapes
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3.3 Electron Configuration

• Electron Configurations
• Pauli exclusion principle each orbital can hold
  no more than two electrons
• no two electrons can have the same four quantum
  numbers
• Aufbau principle electrons fill orbitals that
  have the lowest energy first
• 1slt2slt2plt3slt3plt4slt3d

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Overlapping Orbital Energies
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3.3 Electron Configuration

• Electron Configurations
• Hunds rule orbitals of the same n and l number
  are occupied by one electron before pairing occurs

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Hunds Rule