Chemical Bonding

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Chemical Bonding
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Chemical Bond

• The attraction between atoms in a molecule or
  crystalline structure
• When elements react atoms must collide
• Nucleus buried in electron cloud
• Nuclei will not collide only electron clouds
  collide

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Metallic Bond

• Bond that results when metal atoms release their
  valence electrons to a pool of electrons shared
  by all the metal atoms
• Holds metals together
• Overlap of orbitals allows outer electrons to
  roam freely through metal (delocalized)
• Results in high conductivity, malleability, and
  ductility

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Ionic Compound

• Composed of positively and negatively charged
  atoms
• Metals on left form compounds with nonmetals on
  right
• Ionic bond - a chemical bond between two ions
  with opposite charges

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• EXAMPLE NaCl

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Properties of Ionic Compounds

• Crystalline
• solids
• High melting and boiling points
• Shatter because they are brittle
• May be water soluble

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Ionic Compounds Representation

• Formula unit for example, NaCl

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Atoms to Ions

• Atoms are electrically neutral because they have
  same number of p and e-
• Gaining or losing 1 or more electrons, the atom
  can be converted into a charged particle called
  ion.
• Ion- an atom or group of atoms that has a
  positive or negative charge

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I love cats?, I hate ants?

• Cations- positive ion, fewer electrons than
  protons, lose electrons
• Positive charge on a cation number electrons
  lost
• Ex. Neutral Mg atom loses 2 electrons? forms
  Mg2 ion
• Anions- negative ion, more electrons than
  protons, gain electrons
• negative charge on nonmetal anion equals the
  number of electrons gained
• Ex. S? gains 2 electrons, sulfide ion S2-

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Oxidation Numbers

• Charge on atom
• Group 1,2,3 A form charges equal to the group
  number (1, 2, 3)
• Nonmetals 5, 6, 7 A have negative charge usually
  equal to 8 A group (-3, -2, -1)
• Monatomic ion
• Single atom that has lost or gained electrons

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Transition and Post-Transition Metal Ions

• More than one stable ion
• Examples
• Fe2 and Fe3
• Cu and Cu2
• Many transition metals form 2 ions.

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Ions and the octet rule

• Octet rule atoms become stable by having 8
  electrons in their outer energy level except some
  of the smallest atoms which have only 2
• Noble gases lack reactivity (stable - filled
  valence electron shell)

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Ions and the octet rule

• Elements become stable by achieving the valence
  electron configuration of 1 of noble gases.
  (Share or transfer electrons)
• Main group metals react to have an electron
  configuration like the noble gas before them
• Main group nonmetals react to have an electron
  configuration like that of the noble gas after
  them

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Lets look at NaCl
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Remember Electron Dot Symbols

• Dots around atomic symbol represent the number of
  valence electrons
• Write electron dot for Radon (Rn), Lead (Pb), and
  Xenon (Xe)

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NaCl Again
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Which Ions Form?
How many electrons must be gained or lost to
satisfy octet rule?
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Formulas of Ionic Compounds

• MUST BE ELECTRICALLY NEUTRAL
• Have the lowest possible number of each type of
  atom (Formula Unit)
• Subscripts indicate number of ions
• Cations always written first and charges are not
  included!!

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Naming Ionic Compounds

• Cation first, anion second
• Cation of Main Group elements
• Simply use the name of element it is formed from
• Ex Na, sodium ion
• Cation of Transition Metals
• Use name of the element it is formed from AND
  charge designated by a Roman Numeral in ( )
• Ex Fe 3, Iron(III)

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Naming Ionic Compounds

• Anion
• Replace ending of name with -ide
• Examples
• fluoride, chloride, bromide
• oxide, sulfide, selenide, nitride, phosphide,
  arsenide

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Naming Ionic Compounds

• Name the following ionic compounds
• MgCl2 FeF3
• LiBr ZnO
• Al2O3 Na2S

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Table 3-8, p.96
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Polyatomic Ions

• Several atoms bound together that collectively
  have a charge
• A polyatomic ions acts just like a monoatomic ion

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Example phosphate ion
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Practice

• Name the following ions
• NO3-
• CN-
• OH-
• Cr2O7

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Practice

• Answers
• Nitrate ion
• Cyanide ion
• Hydroxide ion
• Dichromate ion

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More Practice

• Write the formulas of the following ions
• Phosphate ion
• Ammonium ion
• Permanganate ion
• Oxalate

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More Practice

• Answers
• PO43-
• NH4
• MnO4-
• C2O42-

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Formulas (continued)

• Parentheses may be needed for polyatomic ions
• EXAMPLE
• aluminum hydroxide
• ammonium phosphate
• sodium sulfate

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p.95a
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A Little Trick
Magnesium phosphate
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Writing Formulas Summarized

• 1. List cation first, anion second
• Ex. NaCl not ClNa
• Dont write charges of ions
• Ex. KF not KF-
• Use parentheses around a polyatomic ion formula
  if it has a subscript
• Ex. Al2(SO4)3 not AL2SO4 3

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Practice

• Name the following compounds
• CaO
• NaNO3
• NH4Cl

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Practice

• Answers
• Calcium Oxide
• Sodium Nitrate
• Ammonium Chloride

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More Practice

• Write formulas for the following compounds
• Barium Hydroxide
• Copper (II) carbonate
• Magnesium bicarbonate

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More Practice

• Answers
• Ba(OH)2
• CuCO3
• Mg(HCO3)2

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Lets Practice