CHEM 2040 FUNDAMENTAL ORGANIC CHEMISTRY I Dr' Barry Miburo

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CHEM 2040 FUNDAMENTAL ORGANIC CHEMISTRY IDr.
Barry Miburo

• Chapter 1. STRUCTURE AND BONDING OF CHEMICAL
  SUBSTANCES
• Objective Describe, explain apply the
  principles of molecular structure and bonding

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1.1. Atoms and Elements (Read 1-2, pg 3)

• a. Elements
• Definition element substance made of identical
  atoms.
• Atom simplest entity to make a substance
• ex iron, sulfur, copper

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1.2. Molecules and Compounds

• a. Definition Compound substance made
  of identical molecules.
• Molecule assembly of 2 or more atoms bound by a
  chemical bond.
• ex salt, sugar

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b. Characteristic features of a molecule

• Empirical formula used to show the simplest
  ratios of atoms in the molecule
• Molecular Formula used to show the actual
  numbers of atoms in the molecule
• Molecular mass sum of atomic masses of atoms in
  a molecule. Units amu
• ex NaHCO4 molecular mass 23 1 12 64
  102 amu
• Molar mass mass of one mole of substance.
• Same number as molecular mass.
• Different units grams/mol

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1.3. Chemical Bond.

• http//www.ithacasciencezone.com/chemzone/lessons
  /03bonding/mleebonding/ionic_bonds.htm
• http//www.ithacasciencezone.com/chemzone/lessons
  /03bonding/mleebonding/covalent_bonds.htm
• Chemical bond a force that holds two atoms
  together.
• Bond making process Atoms pair up single
  electrons in their outermost (valence) shell
  orbitals. Goal of bond formation each atom
  reaches increased stability

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a. Ionic Bond

• Formed between ions from metals and nonmetals.
• Cations positively charged ions formed when
  metals lose outer shell electrons.
• Anions negatively charged ions formed when
  nonmetals gain electrons.
• Ionic bond electrostatic attraction between the
  cation and the anion.
• ionic compounds compounds built with ionic bonds
• ex NaCl, made with Na and Cl-

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b. Covalent bond

• Formed between nonmetals.
• Electrons in outer shells are shared between
  bond-making atoms. Reason for sharing similar
  electronegativities.
• Single bond when 2 atoms are bound using 1 pair
  of electrons. ex H2, Cl2,
• Double bond when 2 atoms are bound using 2 pairs
  of electrons. ex O2, CO2
• Triple bond when 2 atoms are bound using 3 pairs
  of electrons. ex N2.

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c. Valence

• Definition ability to form bonds. Determined by
  of single electrons in the valence shell
• Valence Determination Procedure
• - Determine the total number of valence shell
  electrons. Shown by the roman index of the column
• - Place electrons one by one around atom to make
  up to 4 single electrons. Use remaining electrons
  to make lone pairs.               
• Atom   valence shell electrons        of bonds
  possible
• total    single  lone pairs        single 
  double triple
• C         4          4         
  0                      4          2          1

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d. Lewis Structure

• Definition Lewis structure way to draw the
  structure of covalent compounds using dots as
  electrons in bonds and lone pairs
• Drawing guidelines
• Step 1 Draw all atoms showing their valence
  electrons
• Step 2 Determine the central atom. It has the
  highest valence. For atoms from the same column
  in the periodic table, the lowermost in the
  column is the central atom.

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Lewis Structure Drawing Procedure (Continued)

• Step 3
• Pair up single electrons first to form bonds
  between the central and peripheral atoms. Use the
  most electronegative peripheral atoms first. In
  case of two or more identical central atom
  candidates, form chains
• If the central atoms runs out of single
  electrons, use electrons from the its lone pairs
  to form additional bonds.
• Single bonds are formed first. Multiple bonds may
  be formed as needed, leaving just enough single
  electrons to place the remaining peripheral atoms.

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Lewis Structure Drawing Procedure (Continued 2)

• Step 4
• To form anions, add electrons to single electrons
  on appropriate atoms and show the resulting
  charge.
• To form cations, remove single electrons from
  appropriate atoms and and show the resulting
  charge.
• If no valence electrons are left on the central
  atom, add ionic peripheral atoms to account for
  the charge of the polyatomic ion.

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Lewis Structure Drawing Procedure (Examples)

• Examples
• H2PO4(-)
• H2C204
• H6C2N()

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e. Bond and Molecular Polarity

• DEMOS
• http//library.tedankara.k12.tr/webchem/Chemical
  20bonding20and20intermolecular20forces/Bond20a
  nd20Molecular20Polarity.htm
• http//www.wellesley.edu/Chemistry/chem120/vsepr.
  html
• Polar bond between atoms of different
  electronegativities.
• Polar molecule must have
• Polar bonds
• Unbalanced arrangement of bonds around the
  central atoms

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Bond and Molecular Polarity (Examples)

• BF3 and NH3
• CH2Cl2 and CHCl3
• CO2 and H2O

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1.4. Formation of Molecular Orbitals

• Case study C
• Valence of C ?
• Meaning what in terms of valence shell electrons?
• What and how many orbitals in valence shell?
• Orbital energies are they the same or different?
• Results of experiments on CH4. C-H bond strength
  108 kcal/mol.
• Meaning C has 4 C-H bonds of equal strength
• Fact reconciliation
• Valence shell orbitals of C alone and C inside
  CH4 are they the same or different?

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Hybridization

• Demo
• http//www.colby.edu/chemistry/OChem/DEMOS/Orbita
  ls.html
• Image sphybridPicture1 (pg 46)
•  Definition hybridization process of
  reorganization of valence shell atomic orbitals
  (AOs). Result
• Same of new hybrid AO's of same energy
• reorganization of electron configuration to
  reflect the new situation

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a. sp3 Hybridization Single bond formation

• Picture sp3hybridnPicture1 (pg 48)
• Definition hybridization that uses 1 s 3 p
  atomic orbitals
• Result formation of 4 new hybrid AO's of same
  energy.
• Geometric arrangement in a tetrahedron shape, in
  3-D space at 109o apart
• ex C
• hybridized atoms can react form bonds with
  other atoms

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sp3 Hybridization Single Bonds (Continued)

• Image sp3hybridnsmgbondPicture1 (pg 49)
• Sigma(s) bond formed between
• 2 hybrid orbitals on same axis (pg 54).
• 1 hybrid orbital and an s orbital (pg 49)
• single bond  lone s-bond between 2 atoms
• Structural representation single bond is shown
  as a single line

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Single Bonds (Examples)
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b. sp2 Hybridization Double bond formation.

• Images sphybridPicture1 (pg 46)
• Definition Hybidization that uses 1 s 2 p
  orbitals.
• Result
• 3 hybrid AO's. code name sp2
• one p orbital is left out of the hybridization
  process. sticking out in center of plane at right
  angle
• Geometric arrangement of the hybrid orbitals in
  plane at 1200 from one another

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Bonds formed by sp2 hybridized atoms

• Image sp2sgmpibondsPicture1(pg 45)
• Components
• s-bonds using hybridized orbitals in coaxial
  orientations (pg 54)
• pi(p)- bonds using hybridized orbitals in
  parallel axes positions (sppibondPicture1, pg 44)
• Double bond sgm pi bonds on same axis
• Structural representation Double bond is shown
  as a double line

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Sp2 hybridized molecules
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c. sp Hybridization

• Image sphybridPicture1 (pg 46)
• Definition hybridization that uses one s one p
  orbitals
• Result
• two hybrid orbitals
• two non hybridized p orbitals
• Geometry of hybrid orbitals in line at 180o from
  each other

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Sp Hybridization and triple bond formation

• Image spsgmpibondsPicture1 (pg 52)
• triple bond made of one sigma two pi bonds in
  the same space
• Structural notation triple line
• ex acetylene

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Sp hybridized molecules
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1.5. Structural Representation of Molecules

• Kekule's notation 4 bonds in cross around C 
• 3-D notation (Van't Hoff-Le Bel)
• two bonds in plane
• wedged line used to show a bond out of plane
  directed toward the viewer
• dotted line used to show a bond out of plane
  directed away from viewer

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Structural Representation (Examples)
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Structural Representation of Molecules (Continued)

• Skelettal notation C H not shown. Presence of
  C implied at corners and ends of bonds. Presence
  of H implied at every C site to complete C's
  valence 
• Stick-and-Ball sticks for bonds, balls for atoms
• used on solid and computer models
• Space filling atoms glued to one another
• ISIS DRAW Program used to draw molecular (Lewis)
  structures