Chapter 3 Atoms and Elements

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Chapter 3Atoms and Elements
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Understanding the Macroscopic World

• The connection between the microscopic atom and
  the macroscopic element is the key to
  understanding the chemical world.

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Atoms

• An atom is the smallest identifiable unit of an
  element.
• Similarities and differences on the atomic scale
  correlate with similarities and differences on
  the macroscopic scale.

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Atoms
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Protons Determine the Element

• The atomic number, Z, represents the number of
  protons in the nucleus of an atom.
• The charge of a proton is assigned numerical
  value of 1.
• Protons constitute a significant part of the mass
  of an atom.
• Mass of a proton is 1.0 amu

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Chemical Symbols

• Symbols are an abbreviation of the chemical name
  which can be based on
• The English name for the element hydrogen ? H
• The Greek or Latin name ferrum (iron) ? Fe
• Their place of discovery europium ? Eu
• The scientist honored by the naming curium ? Cm

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Periodic Table of Elements
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Electrons

• A neutral atom has as many electrons outside its
  nucleus as protons within its nucleus.
• The opposing charges of protons and electrons
  hold electrons within a spherical region
  surrounding the nucleus.
• Atoms can lose and gain one or more electrons.

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Determining Protons and Electrons
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Neutrons

• Neutrons are almost as massive as protons but
  carry no electrical charge.
• The number of neutrons in the atoms of an element
  can vary resulting in ISOTOPES.
• Can be naturally occurring or man-made
• The sum of neutrons and protons in an atom is
  called the mass number of the atom.

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Atomic Mass

• Atomic masses listed on the periodic table are
  weighted averages of the masses of each naturally
  occurring isotope for that element.
• Silver has two naturally occurring isotopes. One
  has a mass of about 107 amu and the other has a
  mass of about 109 amu.
• Silver -107 has an abundance in nature of 51.84.
• Silver -109 has an abundance in nature of 48.16.

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Atomic Mass

• Calculate the average atomic mass of silver.
• Silver has two naturally occurring isotopes.
• One has a mass of 106.90509 amu (abundance in
  nature of 51.84.)
• The other has a mass of 108.90476 amu (abundance
  in nature of 48.16.)
• 106.90509 amu ( 0.5184) 55.42 amu
• 108.90476 amu (0.4816) 52.45 amu
• 107.87 amu

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Molar Mass

• Calculate the Molar Mass of Calcium carbonate
• The mass of one mole of a compound.
• Calcium carbonate
• Chemical Formula ? CaCO3
• Calcium 40.08 grams X 1 mole 40.08
  grams
• Carbon 12.01 grams X 1 mole 12.01 grams
• Oxygen 16.00 grams X 3 moles 48.00 grams
• 100.09 grams

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Periodic Law

• Mendeleev listed the known elements in order of
  increasing atomic mass, grouping those with
  similar properties.
• He noticed that certain similar properties would
  recur in a periodic fashion.
• His tabulation is the precursor to our modern
  periodic table.

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Mendeleev and the Periodic Table

• Proposed that elements would be discovered to
  fill in gaps in the table.
• Proposed that some measured atomic masses were in
  error.
• Summarized a large number of observations
• The underlying reasons for periodic behavior were
  as yet unknown
• The Bohr model and the quantum mechanical model
  were needed to explain the observations.

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The Bohr Model

• This is a MODEL of the atom that links electron
  behavior (microscopic) to the periodic law
  (macroscopic).

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Bohr Diagrams/Electron Configurations

• Based on the behavior of electrons as particles
• Electron orbits
• Specified with n, the orbits quantum number
• Fixed energies
• Fixed radii
• Maximum number of electrons based on n
• This model is an oversimplification (as are most
  models).

• Atoms with full outer orbits are extremely
  stable.
• Atoms with outer orbits that are not full are
  unstable and will undergo chemical reactions
  attempting to fill the outer orbit.

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The Quantum Mechanical Model

• Based on the behavior of electrons as waves
• Replace Bohrs orbits with orbitals, a
  representation of electron location as the
  probability of finding it in a certain region of
  space.
• Orbitals are grouped into shells and fill
  similarly to Bohrs orbits.

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Determinism and Quantum Mechanics

• Specifics of orbital filling are beyond the scope
  of this textBUT
• The statistical nature of the quantum mechanical
  model rocked the scientific establishment.
• An indeterminate universe
• Both models are useful even though Bohrs, by
  experiment, has been shown to be invalid.

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Families of Elements

• Also called groups
• Based on outer electron configurations
• Vertical columns
• Alkali metals
• Alkaline earth metals
• Chalcogens
• Halogens
• Noble gases

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Element Families
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Metals, Nonmetals, and Metalloids
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Molecular Elements

• Some elements occur as diatomic molecules.

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The Mole Concept

• Counting particles as small as atoms is
  impractical.
• The mole concept allows us to relate the mass of
  a sample of an element to the number of atoms
  within it.
• The unit of comparison is called a mole and
  corresponds to 6.022 x 1023.

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Avogadros Number

• Determined such that the numerical value of the
  atomic mass of an element in amu is equal to the
  molar mass of that element in grams per mole.
• These relationships of grams, moles, and atoms
  can be used as conversion factors.

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Chapter Summary

• Molecular Concept
• Atomic Number and Mass Number
• Isotopes
• Molar Mass
• Bohr Model
• Quantum Mechanical Model
• Orbitals

• Societal Impact
• Chemical processes that cause change are caused
  by changes in atoms or molecules.
• Pollution results from misplaced atoms. Atoms
  that are not where they are supposed to be
  located.
• Models are used to describe nature.