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CHEM 0310: STUDY GUIDE
valence electrons
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the electrons in the outer shells of atoms that can participate in bonding. Each element generally forms certain fixed numbers of bonds: valence
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Lewis Structures
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electron dot formulas that show the valence electrons of atoms. lone-pairs are often omitted
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octet rule
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most 2nd and 3rd row elements prefer an eight (8) electron configuration i bonding (noble gas configuration)
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Constitutional isomers
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molecules with identical formula, but different connectivity between the atoms
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electronegativity
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the ability of an atom to attract electrons. The Pauling scale ranges from 4.0 (strongest, F) to 0.7 (weakest, Cs). The electron distribution within the bond reflects a continuum from covalent to ionic and is a function of the electronegativity of the bonded atoms
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Electronegativity
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Affinity for electrons
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H electronegativity
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2.2
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C electronegativity
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2.6 |
N electronegativity
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3.0
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O electronegativity
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3.4
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F electronegativity
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4.0
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resonance structures
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chemical structures that differ only in the distribution of the π bond electrons
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orbitals
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plots of the square of the wave function (ψ2) that express a high probability of finding an electron within its perimeter.
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nodes |
positions in space where ψ=0; the greater the number of nodes the higher the energy of the orbital
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hybridization
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combination of individual wave functions for s and p orbitals to obtain wave functions for new orbitals; sp3 ,sp2 ,sp (σ and π bonding)
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dipole moment
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a function of charge separation; equals distance times (partial) charge. Polar molecules have a dipole moment, but apolar molecule can also contain polar bonds whose dipole moments cancel each other.
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molecular formula
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C4H10O
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condensed structural formulae
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(CH3)2CHCH2OH or HOCH2CH(CH3)2
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|
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lewis dot structure
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|
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Bond-line formula.
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alkanes |
parent compounds; methane, ethane. rotation around the C-C σ bond is easy. σ bonds have cylindrical symmetry
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alkenes
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parent compound; ethene. Rotation around the C=C π bond is impossible without breaking the bond (activation energy is approx 60 kcal/mol) Therefor cis- and trans- stereoisomers occur. π bonds have a nodal plane.
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alkynes |
parent compound; ethyne. the C,C triple bond contains one σ bond and two π bonds. the two π bond orbitals are orthogonal
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arenes |
arenes |
intermolecular forces
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electrostatic interactions (ionic and dipole-dipole), Hydrogen bonding, Van der Waal,
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solubilities |
polar solvents dissolve polar molecules and salts via dipole-dipole interactions and H-bonding. Apolar solvents dissolve apolar molecules via van der waals foreces. "like dissolves like"
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What is organic chemistry?
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Study of Carbon + its compounds
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What are the key elements of organic chemistry?
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1. Structure
2. Function
3. Relationship
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Concept of Valency
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-All atoms have fixed bonds.
-Group # = # valence electrons
4 bonds = tetravalent
3 bonds = trivalent
2 bonds= divalent
1 bond = monovalent
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Trend of Electronegativity
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Up + Right
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Ionic Bonds
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Widely different electronegativities
-Charged attraction (+) attracts (-)
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Covalent Bonds
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Sharing Electrons
-Same Atom/Same electronegativity.
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Polar Covalent Bond
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-Dipole movement
-Polar - Unbalanced charge
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Bronsted-Lowry Acid
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Proton Donor
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Bronsted-Lowry Base
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Proton Acceptor
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What is the strongest base in water ?
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OH-
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What is the strongest acid in water?
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H30+
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What is Ka? How is it measured?
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Ka = Keq * [H20]
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How is pKa measured?
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-log[Ka]
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Ka and Equilibrium
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Big Ka = favors products
Small Ka = favors reactants
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Relationship between Ka and pKa
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Strong Acid:
- Big Ka
- Small pKa
Weak Acid
-Small Ka
-Big pKa
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Acidity in columns are determined by....
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Bond strength!
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Acidity in rows determined by...
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Electronegativity
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S orbitals stabilize...
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(-) charge
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H-H bond dissociation energy
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104kcal/mol
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H3C-H bond dissociation energy
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105kcal/mol
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H3C-I bond dissociation energy
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57kcal/mol
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H3C-F bond dissociation energy
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110kcal/mol
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H3C-Cl bond dissociation energy
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85kcal/mol
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H3C-Br bond dissociation energy
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70kcal/mol
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(CH3)3C-H bond dissociation energy
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96.5kcal/mol
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Cl-Cl bond dissociation energy
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58kcal/mol
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Cl-H bond dissociation energy
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103kcal/mol
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H-H eclipsing energy
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1kcal/mol
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H-CH3 eclipsing energy
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1.2kcal/mol
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CH3-CH3 eclipsing energy
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2.9kcal/mol
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CH3-CH3 gauche energy
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0.9kcal/mol
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Li electronegativity
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1.0 |
Cl electronegativity
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3.2
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F radical formation energy
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-103kcal/mol
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I radical formation energy
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13kcal/mol
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Cl radical formation energy
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-25kcal/mol
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Br radical formation energy
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-6kcal/mol
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HI pKa value
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-10
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HBr pKa value
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-9
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HCl pKa value
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-8
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H2SO4 pKa value
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-3
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H3O+ pKa value
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-1.7
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HNO3 pKa value
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-1.4
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CH3SO3H pKa value
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-1.2
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HF pKa value
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3.2
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CH3COOH pKa value
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4.7
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HCN pKa value
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9.2
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NH4+ pKa value
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9.3
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CH3SH pKa value
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10
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CH3OH pKa value
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15.5
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H2O pKa value
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15.7
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NH3 pKa value
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35
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CH4 pKa value
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~50
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Csp3-H bond length
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1.1A
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C-C bond length
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1.5A
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C=C bond length
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1.3A
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C-I bond length
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2.1A
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C-O bond length
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1.4A
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O-H bond length
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1.0A
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C=O bond length
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1.2A
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Csp-Csp bond length
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1.2A
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C-Cl bond length
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1.8A
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C-Br bond length
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1.9A
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