Valence%20Electrons%20and%20Chemical%20Bonding

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Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions

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Take Home Message

• When atoms combine to produce molecules and
  compounds, expect the chemical properties of the
  molecules/compounds to be far different than that
  of the constituent atoms (hierarchy theory)
• Atoms bind together by re-arranging and sharing
  their electrons
• Ionic bonds
• Metallic bonds
• Covalent Bonds
• Intermolecular forces (e.g., hydrogen bond)
• Chemical interactions make and break bonds
  between atoms and in so doing effect a change in
  energy (potential and kinetic)
• Weak chemical bonds (e.g., covalent bonds) play a
  very important role in the chemistry of life

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Chapter Deletions

• Pp 262 (Covalent compounds and formulas) 265
  (Coordinate covalent bonds)
• Pp 267 (Ionic compound names) 270 (Covalent
  compound names)
• Pp 279 (Percent Composition of Compounds) 295
  (Quantitative use of equations)

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Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions

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Atoms in Proximity Bonds Away

• Hypothesis when two atoms are brought together,
  electrons will tend to re-arrange themselves to
  the lowest energy state where the valence
  electrons are most stable
• Product electrons are re-arranged into bonds
• Give away electrons
• Accept electrons
• Share electrons

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Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions

7
Ionic Bonding

• Atoms give away electrons while other atoms
  receive electrons
• Example of lithium chloride
• 36Li 1735.5Cl LiCl

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Ionic Bonding

• Lithium (Li)
• Li gives up 1 electron and is left with 2
  electrons (-) and 3 protons () net positive ()
  charge
• Chlorine (Cl)
• Cl has 1 unpaired electron in valence shell, so
  Cl tends to accept an electron and is left with
  18 electrons (-) and 17 protons net negative (-)
  charge

9
Ionic Bonding

• Atoms give away electrons while other atoms
  receive electrons
• Example of lithium chloride
• Li Cl LiCl
• Bonding via electrical attraction between Li and
  Cl-
• Li Cl - LiCl-
• Consequence ionic bonds are underpinned by
  charged ions and tend to form crystals of very
  specific and repeating geometry (very rigid)
• Example NaCl is based on ionic bonds and is salt

10
Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions

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Metallic Bonds

• Elements that do not give or take electrons
  (ionic bonds) BUT share electrons
• Valence electrons tend to move freely between
  both atoms (contrast with ionic bonds)
• Significance of sharing electrons compounds tend
  to show two features
• Malleability (easily worked or pounded)
• Conductive of electricity (good conductors)
• Examples
• Gold jewelry
• Copper wire

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Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions

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Covalent Bonds

• Extremes of behavior in bonding
• Accept or give away electrons (ionic bonds)
• No tendency to share (noble gases)
• Intermediate between these two extremes but
• Do not form ionic bonds
• Do not form metallic bonds
• Yet share 1,2, 3 and 4 electrons in unique
  arrangement called covalent bonds
• Key orbits of valence electrons are shared so
  that electrons are shared (and move) between
  valence shells of adjacent atoms

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Covalent Bonds

• Example of hydrogen fluoride (HF)
• 11H and 919F
• Note Valence shell for both atoms are full
• Single bond shared
• Double bond

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Next Weeks Lab Evaporation and Chemical
Structure

• Vaporization and chemical properties of molecules
• Liquid to gas state change
• State change has energy cost endothermic
  (temperature decrease)
• Temperature change is a function of chemical
  structure of molecule
• Bonding and polarity

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Evaporation and Chemical Structure

• Organic compounds
• Carbon based or hydrocarbons bond with other
  elements via covalent bonds)
• Alkanes C and H only
• Pentane (C5H12)
• Alcohols C, H and OH (hydroxyl group)
• Ethanol (C2H5OH)
• Structural formula
• Hydrogen bonding H bonded to N, O or F (tight
  bond)
• Process as chemical vaporizes, temperature
  change is chemical specific and is a window
  onto the chemical structure

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Evaporation and Chemical Structure

• Hypothesis temperature changes with vaporization
  in a manner that is predictable, based on the
  bonding among atoms involving C, H and OH
• Method
• Measure temperature change electronically
• Record for 5 hydrocarbons
• Analyze data (graphically) based on understanding
  of the bonds for each molecule

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Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions

20
Valence Electrons and Chemical Bonding

• Review valence electrons
• Principles of Bonds Away
• Ionic Bonds
• Metallic Bonds
• Covalent Bonds
• Intermolecular Forces
• Common Chemical Reactions