Introductory Chemistry: Concepts

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Daltons Theory

• A Summary of Daltons Atomic Theory
• An element is composed of tiny, indivisible,
  indestructible particles called atoms.
• All atoms of an element are identical and have
  the same properties.
• Atoms of different elements combine to form
  compounds.
• Compounds contain atoms in small whole number
  ratios.
• Atoms can combine in more than one ratio to form
  different compounds.

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Is it possible to see atoms?
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Daltons Model

• According to the law of definite composition, the
  mass ratio of carbon to oxygen in carbon dioxide
  is always the same. Carbon dioxide is composed of
  1 carbon atom and 2 oxygen atoms.

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Subatomic Particles

• About 50 years after Daltons proposal, evidence
  was seen that atoms were divisible.
• Two subatomic particles were discovered.
• negatively charged electrons, e
• positively charge protons, p
• An electron has a relative charge of -1, and a
  proton has a relative charge of 1.

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Thomsons Model of the Atom

• Thomson proposed that the electrons were
  distributed evenly throughout a homogeneous
  sphere of positive charge.
• This was called the plum pudding model of the
  atom.

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Mass of Subatomic Particles

• Thomson calculated the masses of a proton and
  electron
• an electron has a mass of 9.11 10-28 g
• a proton has a mass of 1.67 10-24 g

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Rutherfords Gold Foil Experiment

• Rutherfords student fired alpha particles at
  thin gold foils. If the plum pudding model of
  the atom was correct, a-particles should pass
  through undeflected. Alpha rays are composed of
  helium atoms stripped of their electrons (helium
  nuclei).

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Explanation of Scattering
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Rutherford's Model of the Atom

• Rutherford proposed a new model of the atom
• The negatively charged electrons are distributed
  around a positively charged nucleus.
• An atom has a diameter of about 1 10-8 cm and
  the nucleus has a diameter of about 1 10-13 cm.

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Subatomic Particles Revisited
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Atomic Notation

• Each element has a characteristic number of
  protons in the nucleus. This is the atomic
  number, Z.
• The total number of protons and neutrons in the
  nucleus of an atom is the mass number, A.
• We use atomic notation to display the number of
  protons and neutrons in the nucleus of an atom

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Using Atomic Notation

• An example Si
• The element is _____ (symbol Si).
• The atomic number is ____ silicon has ____
  protons.
• The mass number is ___ the atom of silicon has
  ___ protons ___ neutrons.

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Isotopes

• Atoms of the same element that have a different
  number of neutrons in the nucleus are called
  isotopes.
• Isotopes have the same atomic number but
  different mass numbers.
• cobalt-60 is
• carbon-14 is

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Isotopes, continued

• How many protons and neutrons does an atom of
  lead-206 have?
• The atomic number of Pb is 82, so it has 82
  protons.
• Pb-206 has 206 82 124 neutrons.

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Average Atomic Mass

• Copper has two isotopes
• 63Cu with a mass of 62.930 amu and 69.09
  abundance
• 65Cu with a mass of 64.928 amu and 30.91
  abundance

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Periodic Table

• The periodic table shows the atomic number,
  symbol, and atomic mass for each element.

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Radiant Energy Spectrum

• Wavelength is the distance light travels in one
  cycle.
• Frequency is the number of wave cycles completed
  each second

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The Wave/Particle Nature of Light

• In 1900, Max Planck proposed that energy is not
  continuous, but is emitted in small bundles.
  This is the quantum concept.
• Energy has both a wave nature and a particle
  nature.
• An individual unit of light energy is a photon.

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The Quantum Concept

• The quantum concept states that energy is present
  in small, discrete bundles.

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Bohr Model of the Atom

• Niels Bohr speculated that electrons orbit about
  the nucleus in fixed energy levels.
• Electrons are found only in specific energy
  levels, and nowhere else.
• The electron energy levels are quantized.

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Emission Line Spectra

• When an electrical voltage is passed across a gas
  in a sealed tube, a series of narrow lines is
  seen.
• These lines are the emission line spectrum. The
  emission line spectrum for hydrogen gas shows
  three lines 434 nm, 486 nm, and 656 nm.

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Evidence for Energy Levels

• Bohr realized that this was the evidence he
  needed to prove his theory.

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Atomic Fingerprints

• The emission line spectrum of each element is
  unique.
• We can use the line spectrum to identify elements
  using their atomic fingerprint.

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Neon Lights

• Most neon signs dont actually contain neon
  gas.
• True neon signs are red in color.
• Each noble gas has its own emission spectrum, and
  signs made with each have a different color.

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Energy Levels and Sublevels

• It was later shown that electrons occupy energy
  sublevels within each level.
• These sublevels are given the designations s, p,
  d, and f.
• These designations are in reference to the sharp,
  principal, diffuse, and fine lines in emission
  spectra.

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Energy Levels and Sublevels

• The first energy level has 1 sublevel 1s
• The second energy level has 2 sublevels 2s and
  2p
• The third energy level has 3 sublevels 3s, 3p,
  and 3d

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Electron Occupancy in Sublevels

• The maximum number of electrons in each of the
  energy sublevels depends on the sublevel
• The s sublevel holds a maximum of 2 electrons.
• The p sublevel holds a maximum of 6 electrons.
• The d sublevel holds a maximum of 10 electrons.
• The f sublevel holds a maximum of 14 electrons.

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Filling Diagram for Sublevels

• Electrons are arranged about the nucleus in a
  regular manner. The first electrons fill the
  energy sublevel closest to the nucleus.

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Electron Configurations

• The electron configuration of an atom is a
  shorthand method of writing the location of
  electrons by sublevel.
• Fill each sublevel with electrons until you have
  used all the electrons in the atom

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Quantum Mechanical Model

• An orbital is the region of space where there is
  a high probability of finding an atom.

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Shapes of p-Orbitals

• p-orbitals have a dumbbell shape.
• Each of the p-orbitals has the same shape, but
  each is oriented along a different axis in space.

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Chapter Summary

• Atoms are composed of ______, ______, and
  _______.
• The _____ and ______ are located in the nucleus
  and the _______ are outside the nucleus.
• Atoms are mostly _____ space.
• The number of protons is referred to as the
  ______ _______ for the atom.

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Chapter Summary, continued

• All atoms of the same element have the same
  number of ______.
• ______ are atoms with the same number of protons
  but differing numbers of neutrons.
• The _____ ______ for an isotope is the total
  number of protons plus neutrons.
• The _____ ______ of an element is the weighted
  average of the masses of all the naturally
  occurring isotopes.

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Chapter Summary Continued

• Light has both properties of both _____ and
  ______.
• The particles of light are referred to as ______.
• The energy of photons is _______.
• _______ exist around the nucleus of atoms in
  discrete, quantized energy levels.
• Electrons fill energy sublevels, starting with
  the ______ energy sublevel and filling each
  successive level of higher energy.