Chemical Reactions or

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Chemical Reactions or Bonds Away with Valence
Electrons

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

2
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
  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 (No. 9)

• Pp 184 (A Closer look)
• Pp 186 (A Closer Look)
• Pp 188 (Percent Composition of Compounds) 191
  (Ion Exchange Reactions)

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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

5
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

6
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 whereas other atoms
  receive electrons
• Example of lithium (Li) chloride (Cl)
• 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
Ionic Bonding Salt

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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

12
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

14
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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Covalent Bonds Carbon

• 612C is a special case (profoundly important)
• Valence electrons for C are 4 (1 in each orbit)
  and intermediate between giving and accepting
• C - C single covalent bond (1 orbit)
• C
• C - C two covalent bonds involving 2 orbits
• Unique behavior of C C
• C-C-C (or H or N or __)
• C

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Behavior of Valence Electrons Five Options

• No action (e.g., inert gases)
• Give away one or more electrons in valence state
  (positive ion leading to ionic bond)
• Accept one or more electrons to valence state
  (negative ion leading to ionic bond)
• Share an electron with many other atoms without
  respect to an orbit (metallic bond)
• Share one or more electrons plus their orbits
  with another atom (covalent bond)

18
This 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 of molecule

21
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 6 hydrocarbons
• Analyze data (graphically) based on understanding
  of the bonds for each molecule

22
Valence Electrons and Chemical Bonding

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

23
Intermolecular Forces Polarization Hydrogen
Bonding

• Example of water (H2O)
• H H
• O-
• When one molecules distribution of atoms results
  in one side of the molecule having either a or
  charge
• Resulting distribution of charges causes
  adjoining H2O molecule to align itself with and
  charges to be most stable
• Called polarity of molecule (e.g., magnet)
• Relate to lab exercise greater polarity, greater
  bonding and less evaporation (less temperature
  change)

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Intermolecular Forces Van der Waal Forces

• In polarity, specific and rigid and fields on
  each molecule that does not change over time
• When molecules converge, inevitable that
  electrons shift and re-distribute (e.g., planar
  compound)
• In re-distribution, small net attraction between
  molecules arise and two molecules for weak bond
• Graphite pencil lead
• Stack of paper

25
Valence Electrons and Chemical Bonding

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

26
Acid Base Reaction Measurement

• pH scale
• Any increase in H results in more acid solution
  from 7 to 0
• Any increase in OH- results in more basic
  solution from 7 to 14
• Examples
• Rainwater of 5.6 means what?
• Cell pH value of 6-8 means what?
• Importance to biological systems and buffering

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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 (pH)

28
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