Atomic Structure: Images of the Invisible

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Chapter 3 Atomic Structure Images of the
Invisible
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Electricity and the Atom

• Volta invented the first battery in 1800
• Electric current is supplied by chemical reactions

Electrolysis

• Splitting of compounds using electricity
• Electrolyte conducts electricity
• Electrodes
• Cathode negatively charged
• Anode positively charged
• Ions
• Cation is positively charged moves to cathode
• Anion is negatively charged moves to anode

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Cathode Ray Tube

• Pass current through a tube at low pressure
• Used in TV and computer monitors

?J. J. Thomsons Experiment

• Used cathode ray tube to discover negatively
  charged particles

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Cathode Rays

• Emitted by cathode
• Same thing came from different metals
• Electrons
• Negatively charged
• Found their mass-to-charge ratio
• Could not determine mass or charge separately

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Goldsteins Experiment

• Positive ions could flow in the opposite
  direction
• Mass dependent on gas present in the tube

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Millikans Oil-Drop Experiment

• Able to determine the mass of the electron
• 9.1 x 1028 g
• Would take 1 x 1027 to make 1 gram of electrons
• Determined the charge on the electron

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Roentgen

• Studied the glow caused by the cathode ray tube
• Chemically treated paper to glow
• Even through walls!
• Put his hand between the rays and the paper

Discovery of Radioactivity

• Becquerel found that uranium ores would fog
  photographic plates in the dark
• Marie and Pierre Curie isolated other elements
  that behaved like uranium
• Radioactivity spontaneous emission of radiation
  from certain unstable elements

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Types of Radioactivity

• Three commonly found types

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Behavior of Radioactivity
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Rutherfords Experiment
Model Explaining Rutherfords Experiment

• Originally assumed all particles in an atom were
  evenly spread out
• Cannot explain results of his experiment
• Needed new model

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Structure of Atom

• Rutherford suggested
• Most of mass in nucleus
• All the positive charge
• Nucleus protons and neutrons
• Neutrons have mass but no charge
• Very small size compared to the rest of the atom
• The rest of the atom contains the electrons

Subatomic Particles

• Particles smaller than the atom
• Number of protons in element atomic number
• Element all atoms having the same atomic number

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Isotopes

• Atoms having the same atomic number
• BUT differing in number of neutrons

Symbols for Isotopes
A mass number number of protons number
of neutrons number of nucleons Z atomic
number X symbol of the element Isotopes of
hydrogen
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Example 3.1  Number of Neutrons
235 92
How many neutrons are there in the U
nucleus?
There are 143 neutrons in the nucleus.
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Conceptual Example 3.3  Isotopes
(a) Which of the following are isotopes of the
same element? (We are using the letter X as the
symbol for all elements so that the symbol will
not identify the elements.) (b) Which of the five
isotopes have the same number of neutrons?
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Flame Tests

• Various elements placed in a flame will change
  the color of the flame
• Different colors present in fireworks
• Typically see several colors
• Implies something about the structure of the atom

Bohrs Explanation

• Light can have only discrete amounts of energy
• Energy is quantized
• Electron can have only these values and no others

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Ground and Excited States

• Electrons prefer to be in the lowest energy
  level
• levels closest to the nucleus
• Ground state
• Excited state
• electron goes from the lowest energy level to a
  higher energy level

Energy Levels

• Specified energy value for an electron
• Shifts to lower energy levels give rise to light

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Shells

• Elements may have more than one electron
• Placed into shells
• Shells numbered 1, 2, 3,
• Have 2n2 electrons/shell
• How many electrons in third shell?

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Example 3.4 Electron Shell Capacity
What is the maximum number of electrons in the
fifth shell (fifth energy level)?
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Filling Shells

• Add electrons to the lowest shell until filled,
  then go to the next shell

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Orbitals

• Schrödingers model probability of finding
  electron in a given volume
• Orbitals
• Electron clouds
• Different shapes for different types of orbitals

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Subshells

• Each orbital can contain two electrons
• Orbital shape determines subshell
• Can have s, p, d, f, g, sublevels

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Example 3.6  Subshell Notation
Without referring to Table 3.3, use subshell
notation to write out the electron configuration
for (a) oxygen and (b) sulfur. What similarity of
features do the electron configurations exhibit?
b. Sulfur atoms have 16 electrons each. The
electron configuration is 1s22s22p63s23p4. Note
that the total of the superscripts is 16 and that
we have not exceeded the maximum capacity for any
sublevel.
Both O and S have electron configurations with
four electrons in their highest energy sublevel
(outermost subshell).
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Electron Configuration

• Shells and subshells are filled from the lowest
  shell/subshell
• Electron configuration of nitrogen

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To fill for an element, follow this flow chart
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Electron Configurations and Periodic Table

• Each column is a group or family
• Elements in each group have similar properties
• Common groups alkali metals, alkaline earth
  metals, halogens, and noble gases
• Each row is a period
• Properties vary across each

Outer Electron Configurations

• Valence electrons electrons in outermost shells
• Determines chemistry
• Elements in the same group have the same number
  of valence electrons
• Examples
• Alkali metals 1 valence electron
• Alkaline earth metals 2 valence electrons
• Halogens 7 valence electrons

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Periodic Table

• Blocks
• Correspond to different subshells
• s and p block Main group elements
• d block transition metals
• f block inner transition metals

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Periodic Table

• Metals
• Characteristic luster
• Good conductors of heat and electricity
• Solid at room temperature, except mercury
• Nonmetals
• Dull in appearance
• Poor conductors of heat and electricity
• Metalloids
• Properties between the other classes