Chemistry: Matter and Chemical Bonding

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ChemistryMatter and Chemical Bonding

• Early Atomic Theories

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Timeline. . . . .

• Ancient Greeks (approx 450 BC)
• "Four Element" Theory Earth, Air, Fire, Water

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Benefits

• First suggestion that substances were actually
  made up of a combination of different "elements."

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Democritus

• 400 BC Democritus
• "The smallest indivisible particle of matter is
  the 'atom' "
• No evidence based on thought
• However, the "4 element" theory lingered for
  almost 2000 years! (YIKES)

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Democritus Model
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John Dalton (1809)

• All matter is composed of indivisible particles
  called atoms.
• All atoms of a given element are identical atoms
  of different elements have different properties.
• Chemical reactions involve the combination of
  atoms, not the destruction of atoms.
• When elements react to form compounds, they react
  in whole-number ratios.
• Dalton's atomic theory supported previous
  research. Lasted almost a century!

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Model Indivisible billiard ball
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J.J. Thomson (1897)

• Used the work of other scientists that showed
  that atoms contain charges, and his own work with
  cathode ray tubes, to develop a modified atomic
  theory.
• Atoms are positive spheres, with negative
  particles (electrons) embedded in them.

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Model Raisin bun
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Ernest Rutherford (1911)

• Student of Thomson disagreed.
• Gold Foil Experiment
• Alpha radiation (positive) were shot at a piece
  of gold foil.
• Most of the alpha particles passed through the
  foil, suggesting that most of matter is empty
  space!
• Some particles were deflected back at angles
  they had come in contact with something very
  dense!

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Gold Foil Experiment
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Leading to..Nuclear Model

• Rutherford dense core of positive charge
  (nucleus), with negative electrons orbiting
  around the nucleus.
• Later experiments showed that the positively
  charged particles, now called protons, have an
  equal but opposite charge to the electrons, and
  have a mass 1836 x greater!
• The neutron and the existence of isotopes were
  also discovered

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Niels Bohr

• Worked with Rutherford
• Used atomic spectrum information to place
  electrons in energy levels around the nucleus

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Spectroscope
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How it works.

• Each element has a unique emission spectrum
• When electrons are given energy, they jump to a
  new energy level
• When they fall back down, they emit this extra
  energy as light
• Lines on an emission spectrum represent jumps
  between energy levels.

DEMO
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Emission Spectra
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Modern View of the Atom

• Dense nucleus containing
• () protons
• Neutral neutrons
• Shells of small (-) electrons orbiting the
  nucleus

2 e- in 1st orbital 8 in 2nd 8 in 3rd (until next
year)
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Subatomic Particle Charge Location Size
Proton (p) Positive Nucleus 1
Neutron (n0) Neutral Nucleus 1
Electron (e-) Negative In Orbit 1_ 2000
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Atomic Number of protons of electrons in
a neutral atom

• Atomic mass / Mass Number
• Use rounded values
• 26.98 -gt 27
• 28.09 -gt 28
• 30.97 -gt 31

Mass number protons neutrons
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Isotopes

• Atoms of the same element have the same of
  protons
• The of neutrons can differ
• The same element with a different of neutrons
  are called isotopes
• Radioisotopes are unstable and decay creating
  radioactivity
• Average atomic mass takes the masses of all
  isotopes into account.

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Standard Atomic Notation

• C
• mass is 12
• atomic is 6
• therefore, this carbon has 12 - 6 6 neutrons

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6
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Groups on the periodic table