Lexi Eyerman – AP CHEM SUMMARY
17 Oct. 2011
AP CHEMISTRY: UNIT 3 [pgs. 274-363, chapters 8-9]
I.
Scientific Laws, Theories, and BIG Ideas
a. Chemical Bonds
i. Ionic: electrons transfer; metals and nonmetals; exothermic (violent
reactions); stable compounds; lattice energy – energy to separate a
mole of solid ionic compound into a gas (explained by Coulomb’s law)
ii. Covalent: electrons share; nonmetals; weaker bonds with low m.p.
iii. Metallic: sea of mobile electrons; good conductors of electricity;
malleable and ductile
b. Bond Polarity and Electronegativity
i. Nonpolar Covalent: e- are equally shared; diatomic elements (no dif. in
electronegativity)
ii. Polar Covalent: e- are unequally shared; dif. in electronegativity
1. More electronegative atom is slightly negative in a bond
2. More dif. in electroneg. = shorter bond length (more ionic)
iii. Coordinate Covalent: 2e- coming from just one atom to form a bond
c. Lewis Dot Structures
i. RULES:
1. Count all e-, write symbols (1st in center unless H), complete
octets on non-central atoms
2. Put extra e- on central atoms, and if not enough e-, try multiple
bonds
3. Use formal charges if more than one option
4. Ionic bonds: use brackets and charges (ex/ NaCl: [Na]+[ Cl ]- )
ii. EXCEPTIONS:
1. Ions or molecules w/ odd # of e-: relatively rare and unstable
(ex/ NO)
2. Ions or molecules w/ less than an octet: ex/ BF3: giving boron an
octet would place negative charge on B and positive on F, so B
only has 6e3. Ions or molecules with an expanded octet: Atoms in 3rd period an
below can expand octet presumably through d orbitals that
participate in bonding (ex/ PCl5)
iii. FORMAL CHARGES: Use to identify ideal molecule structure (LDS);
formal charge = # of valence e- – (nonbonding e-)+(½ bonding e-); see
that negative values are on more electronegative atom
d. Bond Enthalpies
i. The enthalpy change (H) for breaking a particular bond (in moles of
that substance) – energy required to break a bond
ii. Bond enthalpies of a reaction: add up all enthalpies of bonds in
reactants and subtract the sum of all the enthalpies of all the bonds in
the products
iii. Negative value means reaction is exothermic; positive is endothermic
e. VSEPR (Valence-shell electron-pair repulsion) (see pg. 321 & 324 for table)
Lexi Eyerman – AP CHEM SUMMARY
17 Oct. 2011
i. Electron domain: region where electrons will most likely be found
ii. Electron domain geometry: arrangement of e- domains around central
atom; includes both bonding and nonbonding domains
iii. Molecular geometry: actual shape of molecule based only on bonding eiv. Nonbonding e- pairs take up more space than bonding electrons
v. Multiple bonds take up more space than single bonds
f. Hybridization: the process of mixing and changing atomic orbitals as atoms
approach each other to form bonds; explains geometries of molecules
i. sp hybrid: if s atomic orbital is full, there are no unshared e-, so it
appears it won’t want to bond; 1 s e- is promoted to the p orbital, and 1
s orbital and 1 of the p orbitals combine to form 2 sp orbitals
ii. sp2 hybrid: mix 1 s orbital with 2 p orbitals; forms 3 sp2 orbitals
iii. sp3 hybrid: mix 1 s orbital with 3 p orbitals; forms 4 sp3 orbitals
iv. sp3d hybrid: 1 s, 3 p, and 1 d orbital; forms 5 sp3d orbitals
v. sp3d2 hybrid: 1 s, 3 p, and 2 d orbitals; forms 6 sp3d2 orbitals
vi. DETERMINING HYBRIDIZATION: Draw LDS, determine VSEPR shape,
see which hybrid is needed
g. Multiple Bonds:  = end to end overlap;  = side to side overlap
i.  is stronger than  b/c sigma has more overlap of eii. Delocalized e-: the bond is not found in one location but moves around
II.
Equations/ Calculations:
a. Formal Charge = valence electrons – (unshared e- + ½ bonding e-)
b. Bond enthalpy of a reaction:
∆𝐻𝑟𝑥𝑛 ∑(𝑏𝑜𝑛𝑑 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑖𝑒𝑠 𝑜𝑓 𝑏𝑜𝑛𝑑𝑠 𝑏𝑟𝑜𝑘𝑒𝑛) − ∑(𝑏𝑜𝑛𝑑 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑖𝑒𝑠 𝑜𝑓 𝑏𝑜𝑛𝑑𝑠 𝑓𝑜𝑟𝑚𝑒𝑑)
III.
Favorite Topic/ Activity: Lewis Dot Structures were my favorite activity; they
help me to visualize the bonds in the molecule (and I do well with visual aids)
IV.
Least Favorite Topic/ Activity: Hybridization was my least favorite activity; they
were hard to understand visually for me (and I wasn’t there when it was
taught… making it that much harder to understand).