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CH 1: Structure and Bonding. Renee Y. Becker CHM 2210 Valencia Community College. Organic Chemistry (present definition): the chemistry of carbon compounds Organic Chemistry (Historical definition):
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CH 1: Structure and Bonding Renee Y. Becker CHM 2210 Valencia Community College
Organic Chemistry (present definition): • the chemistry of carbon compounds Organic Chemistry (Historical definition): • Study of compounds extracted from living organisms, study of compounds having the vital force Vitalism: • The belief that natural products needed a “vital force” to create them • In the 19th century experiments showed that organic compounds could be synthesized from inorganic compounds
Friedrich Wohler • In 1828, Wohler synthesized urea from ammonium cyanate Ammonium cyanate (inorganic)
Natural Product or Synthesized • Plant-derived compounds and synthesized compounds are identical (almost) • You can tell them apart by 14C dating • Synthesized compounds have a lower content of radioactive 14C, their 14C has decayed over time • BUT, plant-derived compounds are recently synthesized from CO2 in the air and therefore have a higher content of radioactive 14C
Not all carbon compounds are organic • Diamonds, graphite, CO2, NH4+-OCN, Na2CO3 • Derived from minerals and have inorganic properties • Most of the millions of carbon compounds are classified as organic
Electronic Configurations • Aufbau principle: Place electrons in lowest energy orbital first. • Hund’s rule: Equal energy orbitals are half-filled, then filled.
Example 1: Electron Configuration Draw electron configuration • Cl • Cl- • Mg • Mg2+ • Fe3+
Bond Formation • Ionic bonding: electrons are transferred. • Covalent bonding: electron pair is shared.
Lewis Structures • Bonding electrons • Nonbonding electrons or lone pairs Satisfy the octet rule!
Example 2: Lewis Dot Structures Draw Lewis structures for the following a) NH3 b) CH3CH2F c) CH3OCH3 d) BF3 e) C3H4
Calculating Formal Charge Formal charge = (# own valence electrons in free atom)-(# own valence electrons in bonded atom) Put in formal charges
Example 3: Lewis Dot Structures Draw the Lewis structure for the following compounds or ions, showing formal charges a) (CH3)+ b) (CH3)- c) NH4Cl d) H3O+ e) (CH3)2NH2Cl
Valence Bond Theory 1. Covalent bonds are formed by overlapping of atomic orbitals, each of which contains one electron of opposite spin. 2. Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms. 3. The greater the amount of orbital overlap, the stronger the bond.
Valence Bond Theory • Linus Pauling: Wave functions from s orbitals & p orbitals could be combined to form hybrid atomic orbitals.
sp hybrid: acetylene Bond angle 180 Electron pair Geometry linear
sp2 hybrid: Ethylene Bond angle 120 (varies) Electron pair Geometry Trigonal Planar
sp3 hybrid: Ethane Bond angle 109.5 (varies) Electron pair Geometry Tetrahedral
Example 4: Hybridization What is the hybridization of the non-hydrogen atoms?
Molecular Orbital Theory • The molecular orbital (MO) model provides a better explanation of chemical and physical properties than the valence bond (VB) model. • Atomic Orbital: Probability of finding the electron within a given region of space in an atom. • Molecular Orbital: Probability of finding the electron within a given region of space in a molecule.
Molecular Orbital Theory • Additive combination of orbitals (s) is lower in energy than two isolated 1s orbitals and is called a bonding molecular orbital.
Molecular Orbital Theory • Subtractive combination of orbitals (s*) is higher in energy than two isolated 1s orbitals and is called an antibonding molecular orbital.
Molecular Orbital Theory • Molecular Orbital Diagram for H2:
Molecular Orbital Theory • Molecular Orbital Diagrams for H2– and He2:
Chemical Formulas Full structural formula (no lone pairs shown) Line-angle formula Skeletal Condensed structural formula Molecular formula Empirical formula • CH3COOH • C2H4O2 • CH2O
Example 5: Chemical Formulas Draw the condensed structural formula for the following 1. 2. 3. 4.
Example 6: Chemical Formulas Draw the skeletal structure • CH3(CH2)4CH3 • CH3CH(CH3)2 • CH3CH(CH3)CH(CH2CH3)CH2CH3 • C(CH3)4