Atomic Properties and Periodic Trends

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Atomic Properties and Periodic Trends

• Electron configurations are responsible for many
  trends in properties.

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Trends to Know

• Atomic size, how measured
• Ionic size, why changes from atom
• Ionization energy--energy required to remove an
  electron from a gaseous atom
• Electron Affinity--energy change when a gaseous
  atom absorbs an electron to form an anion
• Electronegativity-measure of the ability of an
  atom in a molecule to attract electrons to itself

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Atomic Size
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Ionic size, why changes from atom
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Ionization energy--energy required to remove an
electron from a gaseous atom
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Electron Affinity--energy change when a gaseous
atom absorbs an electron to form an anion
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Electronegativity-measure of the ability of an
atom in a molecule to attract electrons to itself
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Paramagnetism

• Diamagnetic--not magnetic, cant be attracted by
  magnetic field
• Paramagnetic--are attracted to magnetic field,
  like magnetite, or Alnico, that can attract
  pieces of iron, steel, and nickel

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Paramagnetism

• Most paramagnetic substances lose their magnetism
  when withdrawn from the magnetic field
• Ferromagnetic--retain their magnetism outside of
  field

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Paramagnetism and ferromagnetism are caused by
electron spins!

• Like the electron has a north and south pole!
• Electron spin is quantized so that only two
  orientations of the electron magnet and its spin
  are possible, so ms 1/2 or - 1/2 .
• Hydrogen--paramagnetic (one electron only)
• Helium--diamagnetic (two electrons only), both
  electrons must be in same orbital, so we say they
  are paired!

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Paramagnetism occurs in substances in which the
atoms contain unpaired electrons. Magnetic
effects arise when unpaired electrons of a
substance align with an external magnetic field.
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Difference between para- and ferro-magnetism

• Paramagnetic unpaired electrons become unaligned
  when removed from field.
• Ferromagnetic unpaired electrons are aligned
  within clusters of atoms, and clusters are more
  or less aligned, remain aligned when removed from
  field.

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Alkali Metals

• Good conductors of electricity
• Low densities
• Grey, shiny when freshly cut with knife
• Very reactive
• Form ionic compounds with nonmetals

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Alkali Metals with Water

• M H2O --gt H2 MOH (memorize)
• Li floats, reacts slowly keeps shape
• Na reacts vigorously, forms small ball that moves
  on surface of water
• K reacts so much it ignites H2 produced burns
  with lilac flame, moves excitedly
• Cs has lowest IE so forms positive ions most
  readily, but trend continues down group.

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Halogens

• Colored, diatomic
• Gas (fluorine and chlorine) to liquid (bromine)
  to solids (iodine and astatine)
• Form ionic compounds w/ M and covalent with NM
• Reactivity decreases down group as atomic radius
  increases and attraction for outer electrons
  decreases. F2 most reactive most electronegative

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Halogens

• React with Group 1 M to form ionic halides
• Most vigorous reaction is between Fr and F. Why?
• Displacement (single replacement)
• Group 1 and group 7 are on opposite sides of PT
  and show opposite trends in reactivities and
  mps.
• Halides insoluble with Ag
• Ag(aq) X-(aq) --gt AgX(s)

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Bonding of Period 3 Oxides

• M to NM shown in Per. 3
• Na2O(s), MgO(s), Al2O3(s)(giant ionic)
• SiO2(s) (giant covalent)
• P4O10(s), SO3(l), Cl2O7(l) (molecular covalent)
• Giant What?

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Acid-base Character of Per. 3 Oxides

• Na2O, MgO Basic
• Al2O3, SiO2 Amphoteric (showing both acidic and
  basic properties)
• P4O10, SO3, Cl2O7 Acidic

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Basic Oxides

• Metal oxides water --gt metal hydroxides
• Na2O(s) H2O(l) --gt 2NaOH(aq)
• What if MgO reacts?
• MgO H2O --gt Mg(OH)2
• Metal oxides acid --gt salt water
• Li2O 2HCl --gt 2LiCl H2O
• Try MgO with HCl.
• MgO 2HCl --gt MgCl2 H2O

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Acidic Oxides

• Nonmetal oxides water --gt acid
• Hint keep oxidation number of NM same
• P4O10 6H2O --gt 4H3PO4
• Try SO3 water.
• SO3 H2O --gt H2SO4
• Try SO2 water.
• SO2 H2O --gt H2SO3

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Amphoteric Oxides

• Al2O3 behaves as base when reacting with acid,
  but with acid when reacting with base.