CEM 141 Exam 3 (1)

CEM 141 Exam 3
-Valence electrons of one atom attracted to nucleus of other atom
-Electrons are located between nuclei
-Bond formation lowers the PE of the system and stabilizes the system. - ANS-Covalent Bonds

-Forms four bonds.
-Can bond with C,H,O,N,S,P
-Properties of these compounds are emergent. - ANS-Why is carbon so important?

-The idea that covalent bonds are formed when orbitals of different atoms overlap -
ANS-Valence Bond Theory

hybridized; sp3 hybridization on the carbon atom - ANS-CH4 forms ____________ orbitals

- ANS-Draw CH4

1. Sum of valence electrons.
2. draw skeleton structure.
3. Use 2 e- for each bond.
4. Make sure each atom (except H) has 8 electrons by adding lone pairs.
5. If there are not enough electrons form multiple bonds. - ANS-Drawing Lewis Structures (rules)

molecules that have the same type and number of atoms but are bonded together in a different
arrangement. - ANS-What is an isomer?

C(n)H(2n+2) - ANS-Generic hydrocarbon formula

free rotation - ANS-Sigma bonds allow ___________ __________ of the bonded atoms

- ANS-Sigma bond

Whenever pi bond is present, then so is sigma bond. - ANS-Pi bond

-Hydrocarbons with one or more carbon-carbon double bonds.
-One sigma bond, one pi bond.
- Restricted rotation around the double bond.
-C is sp2 hybridized. - ANS-Alkenes

-C - sp hybridized
-One sigma bond
-Two pi bonds

, -High electron density between atoms. - ANS-Triple Bonds

Formal charge = (# electrons the atom can use for bonding) - (# electrons the atom "owns"
when bonded)

FC on O = 6 (# valence electrons) - (1/2 x 6) (bonding electrons) - 2 (lone pair electrons)
= 6 -5 = +1 - ANS-Formal Charge

Valence Shell Electron Pair Repulsion.

states that repulsion between the sets of valence-level electrons surrounding an atom causes
these sets to be oriented as far apart as possible - ANS-VSEPR

one - ANS-Multiple bonds - count as _______ center of electron density in VSEPR

-A single bond is always a sigma bond
-All the rest are always pi bonds
-Sigma bonds allow for rotation around the bond
-Pi bonds do not (it would break the pi bond) - ANS-Things to remember about VSEPR...

-sp
-linear
-180 - ANS-2 centers of electron density

-sp2
-trigonal planar
-120 - ANS-3 centers of electron density

-sp3
-tetrahedral
-109.5 - ANS-4 centers of electron density

-sp3d
-trigonal bipyramidal
-90, 120 - ANS-5 centers of electron density

-sp3d2
-octahedral
-90 - ANS-6 centers of electron density

-tetrahedral
-4 centers of electron density - ANS-What is the electron pair geometry around water?

Bent