Of Atoms and Elements

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Of Atoms and Elements

• Historical and Modern Perspectives

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1831 Michael Faraday

• Discovery of ions
• Anion negatively-charged particles
• Cation positively-charged particles
• Science of electrolysis splitting substances
  using electricity
• Determined that atoms were electrical in nature

3
1895 Wilhelm Roentgen

• Studying glow produced from cathode rays
• Noticed that the glow could be transmitted to
  chemically-treated paper
• X-rays discovered, but not fully understood

4
1895 Antoine Bequerel

• Photographic film fogged when placed close to
  samples of uranium
• Required no input of energy
• Graduate student Marie Curie and later her
  husband Pierre continued to study the phenomenon
• Marie coined the term radioactivity

5
1897 Joseph John Thomson

• Showed that the beam created in a cathode-ray
  tube was attracted to a positive plate and
  repelled by a negative plate
• The particles were the same regardless of the
  material from which the ray was generated
• Coined the term electrons for the negative
  particles

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Thomsons Experiment
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Thomsons Model

• Realized that the negatively-charged particles
  had to be balanced by a positively-charged
  substance
• Plum Pudding Model

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ipc/ch05htm/ch05sec1.htm
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1909 Robert Millikan

• Received Nobel Prize in 1923 for work
• Calculated mass and charge of electrons
• Mass 0.000 000 000 000 000 000 000 000 000 000
  911 kg

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illikanoildrop.html
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Millikans Experiment

1. Sprayed oil droplets into a chamber
2. Calculated mass of droplets by how fast they fall
   (gravity)
3. Charge 2 plates-one positive, one negative
4. Oil droplets acquire extra electron by friction
   or x-ray irradiation
5. Oil falls between 2 plates until it stops
   falling positive charge counteracts gravity
6. How much energy necessary in charged plates?

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1910 Ernest Rutherford

• Gold foil experiment

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Rutherford Model

• The atom had to have something very dense and
  positively-charged that was repelling the
  positive alpha particles

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40/Models_of_the_Atom.html
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1913 Neils Bohr

• Built on discoveries of James Chadwick (the
  neutron) and Henry Moseley (atomic number
  number of protons in nucleus)
• Proposed an atom with distinct energy shells
  occupied by electrons around nucleus

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Erwin Schrodinger Current Model

• Less structured, more uncertainty
• Electron cloud representing where electrons are
  most likely to be found

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What Do We Know Now?
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What Do We Know Now?

• Structure of atoms
• Nucleus dense cluster, nearly all the atomic
  mass
• Protons positive charge
• Neutrons no charge
• Electron cloud surrounding nucleus
• Negative charge, in distinct patterns of
  arrangement
• Description of elements
• Atomic number number of protons
• Mass number number of protons neutrons
• Atomic symbol one or two letters

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What Do We Know Now?

• Organization of elements
• Isotopes atoms with the same number of protons,
  but different numbers of neutrons
• Atomic mass average of the masses of all
  isotopes of an element

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What Do We Know Now?

• Notation

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What Do We Know Now?

• Electrons orbit the nucleus in discrete energy
  levels
• Principal quantum numbers represent energy levels
• Lowest numbers closest to nucleus

Electrons CANNOT park between energy levels!
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What Do We Know Now?

• Light behaves as both waves and particles, and
  its behavior is due to atomic structure
• Atoms in ground state can absorb energy and kick
  an electron up to a higher energy level
• Excited state

• An electron can ONLY change state if there is an
  available higher quantum level
• Otherwise, incoming energy will not be absorbed

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What Do We Know Now?

• Energy needed to excite an electron to a higher
  quantum level is very specific

• Falling electrons emit photons with wavelengths
  equal to the amount of energy absorbed

For Example
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Organization of the Atom

• Levels
• Principal quantum number (n)
• Higher number electron energy increases
• Number of electrons allowed
• 2n2

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Organization of the Atom

• Sublevels
• The number of sublevels in an energy level is
  equal to the principal quantum number
• s
• p
• d
• f

Increasing energy
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Organization of the Atom

• Orbitals
• Theoretical 3-D regions of probability
• Where an electron is most likely to exist
• Orbital shapes
• s-orbitals spherical
• p-orbitals dumbbell shaped (2 lobes)
• All orbitals of the same type (e.g. s-orbital)
  have the same shape, but volume depends on energy
  level
• Hold 2 electrons

1s 2s 2p 3p
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Organization of the Atom

• Farther from the nucleus higher energy
  electrons
• Filling order depends on energy

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Organization of Elements

• Read from left to right order of filling
• Remember large atoms will fill an s orbital of
  the next higher energy level before filling a d
  orbital

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Review Atomic Organization

• Atomic spectra give us clues about the
  organization of electrons around the nucleus
• Type of energy given off corresponds to energy
  levels, sublevels and orbitals of electrons

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Organization of Elements

• Electron configuration of oxygen?

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Organization of Elements

• Alkali Metals
• Group 1 (1A) on the Periodic Table
• Except hydrogen, soft shiny metals with low
  melting points
• Good conductors
• React vigorously with water

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Organization of Elements

• Alkaline Earth Metals
• Group 2 (2A) on the Periodic Table
• Shiny metals
• Not as reactive with water as Group 1 elements

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Organization of Elements

• Halogens
• Group 17 (7A) on the Periodic Table
• Strongly reactive
• Form compounds with most of the elements

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Organization of Elements

• Noble Gases
• Group 8 (8A) on the Periodic Table
• All gas
• Highly non-reactive, seldom in combination with
  other elements

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Organization of Elements
Metals, Metalloids, Non-metals
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Quiz Yourself

• Convert 116.3 kg into mg. Record the number in
  regular and scientific notation.
• Refer to the periodic table and name at least one
  element that is
• Noble gas
• Alkali metal
• Alkaline earth metal
• Halogen
• Non-metal
• Metalloid
• Write the full and abbreviated electron
  configuration of
• Silicon
• Manganese
• Potassium
• What is the density of a piece of molybdenum that
  has a mass of 13.2g and a volume of 9.43mL?

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Quiz Answers

• 116,300,000 1.163 x 108
• Noble gas any element in group 18 (8A) on the
  Periodic Table
• Alkali metal any element in group 1 (1A)
• Alkaline earth metal any element in group 2
  (2A)
• Halogen any element in group 17 (7A)
• Non-metal any noble gas, halogen and O, N, C,
  P, S, Se, I
• Metalloid B, Si, Ge, As, Sb, Te, Po, At
• Full electron configuration of
• Silicon 1s22s22p63s23p2
• Manganese 1s22s22p63s23p64s23d5
• Potassium 1s22s22p63s23p64s1
• 1.40 g/mL