To learn about ionic and covalent bonds and explain how they are formed.

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Objectives

1. To learn about ionic and covalent bonds and
   explain how they are formed.
2. To learn about the polar and nonpolar covalent
   bonds.
3. To understand the nature of bonds and their
   relationship to electronegativity.
4. To understand bond polarity and how it is related
   to molecular polarity.

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What is a Chemical Bond?

• Many experiments can determine the fundamental
  nature of materials
• Physical properties such as melting point,
  hardness, and electrical and thermal conductivity
• Solubility characteristics and the properties of
  the resulting solutions.
• For charge distribution, we can study an atoms
  behavior in an electric field.
• Bond strength can be measured by the bond energy
  (energy required to break the bond)

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Chemical Bonds

• Three basic types of bonds
• Ionic
• Electrostatic attraction between ions
• Covalent
• Sharing of electrons
• Metallic
• Metal atoms bonded to several other atoms

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• Molecule a neutral group of atoms that are held
  together by covalent bonds
• Molecular compound A chemical compound whose
  simplest units are molecules
• Chemical Formula Indicates the relative numbers
  of atoms of each kind in a chemical compound by
  using atomic symbols and numerical subscripts
• Molecular formula Shows type and numbers of
  atoms combined in a single molecule of a
  molecular compound
• Diatomic molecule a molecule containing only
  two atoms
• EX O2, H2, Cl2, N2, F2, Br2, I2

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• Bond force that holds groups of atoms together
  and makes them function as a unit
• Bond energy energy required to break a chemical
  bond

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Ionic Bonding
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Ionic Compounds

• Ionic Compound- positive and negative ions that
  are combined so that the numbers of positive and
  negative charges are equal
• Review NaCl Formation
• Not composed of independent, neutral units that
  can be isolated and examined
• Chemical formula represents the simplest ratio of
  the compounds combined ions that gives
  electrical neutrality.
• Formula unit the simplest collection of atoms
  from which an ionic compounds formula can be
  established.
• 1 formulas unit of NaCl one sodium cation plus
  one chloride anion.
• The ratio depends on the charges of the ions
  combined.
• Ionic compound must be electrically neutral.

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A. Types of Chemical Bonds
Ionic Bonding

• Ionic compound results when a metal reacts with a
  nonmetal

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Characteristics of Ionic Compounds

• Very strong attraction between positive and
  negative charges.
• Higher melting, and boiling points that molecular
  compounds
• Do not vaporize at room temp.
• Hard but brittle
• Electrical conductors in the molten and dissolved
  state because ions can move freely to conduct
  electrical charge.

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Energetics of Ionic Bonding

• Electrostatic attraction between the newly-formed
  sodium cation and chloride anion.
• Lattice Energy The energy required to completely
  separate a mole of a solid ionic compound into
  its gaseous ions.

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Characteristics of Ionic Compounds

• Formation favors arrangements in which potential
  energy is minimized
• Na losses an electron and Cl gains it
• Achieved by forming arrangements of a crystal
  lattice
• Distances between ions and their arrangement in a
  crystal represent a balance among attractive and
  repulsive forces
• To compare bond strengths in ionic compounds,
  scientists compare the lattice energy.
• Lattice energy the energy released when one
  mole of an ionic crystalline compound is formed
  from gaseous ions.
• Negative values energy released

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• Lattice energy
• increases with the charge on the ions.
• increases with decreasing size of ions.

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Energetics of Ionic Bonding

• By accounting for all three energies (ionization
  energy, electron affinity, and lattice energy),
  we can get a good idea of the energetics involved
  in such a process.
• A bonding force develops when two different types
  of atoms react to form oppositely charged ions.

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B. Ionic bonding and Structures of Ionic
Compounds

• Ions are packed together to maximize the
  attractions between ions

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B. Ionic bonding and Structures of Ionic
Compounds

• Cations are always smaller than the parent atom

• Anions are always larger than the parent atom

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B. Ionic bonding and Structures of Ionic
Compounds
Ionic Compounds Containing Polyatomic Ions

• Polyatomic ions work in the same way as simple
  ions
• The covalent bonds hold the polyatomic ion
  together so it behaves as a unit

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Metallic Bonding

• The chemical bonding that results from the
  attraction between metal atoms and the
  surrounding sea of electrons.

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Metallic Properties

• Electrons can move, mainly because of the high
  electrical and thermal conductivity of all
  metals.
• Electrons can absorb many frequencies of light
  because they contain many orbitals separated by
  extremely small energy differences. (Excited
  electrons returning to ground level shiny
  appearance of metal surfaces)
• Malleability ability to be hammered or beaten
  into thin sheets
• Ductility ability of a substance to by drawn,
  pulled, or extruded through a small opening to
  produce a wire.
• This is possible because metallic bonding is the
  same in all directions throughout the solid.
• Shifting of layers occurs in one plane so no
  resistance or breaking is encountered, unlike the
  layer of ionic crystals.

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Metallic Bond Strength

• Varies with nuclear charge of the metal atoms and
  the number of electrons in the metals electron
  sea.
• Related to amount of heat of evaporation amount
  required is a measure of the strength of the
  bonds that hold the metal together.
• The higher the heat of evaporation, the stronger
  the metallic bonds.
• When vaporized the bonded atoms in the normal
  solid state are converted to individual metal
  atoms in the gaseous state.