Connections Chemistry Review
October 4, 2021
Hannah Boyce
boyce.h@northeastern.edu
Amanda Dee
Elena Fenstermaker fenstermaker.e@northeastern.edu
Maddie Szoo
Session #4, HW #4
dee.a@northeastern.edu
szoo.m@northeastern.edu
Valence Shell Electron Pair Repulsion (VSEPR) Theory
- Caused by repulsion of electrons between atoms
- Lone pairs affect geometry and angle because they have stronger repulsion than bonding electrons
Chirality
- Chiral: when the mirror image of the molecule is NOT
superimposable on the original structure
(for example, your right hand and your left hand)
- These two structures are known as enantiomers
- NOTE: a molecule is always chiral if it contains a
carbon bonded to four different atoms/groups
- Achiral: when the mirror image of the molecule is
superimposable on the original structure (the two structures
are identical)
Hybridization
- Accounts for molecular geometry and bonding
properties
- Each electron domain of central atom requires one
hybrid orbital
- s and p orbitals combine to form spx orbitals
(sharing electron density)
Connections Chemistry Review
October 4, 2021
Hannah Boyce
boyce.h@northeastern.edu
Amanda Dee
Elena Fenstermaker fenstermaker.e@northeastern.edu
Maddie Szoo
Hybrid Orbital Theory
Averages the valence electron orbitals for each atom
in a molecule
Number of hybridized orbitals = number of combined
valence electron orbitals
σ bond: direct head-on overlap of hybridized orbitals
Session #4, HW #4
dee.a@northeastern.edu
szoo.m@northeastern.edu
Molecular Orbital Theory
Averages the valence electron orbitals for all atoms in
a molecule
Number of molecular orbitals = number of total atomic
valence electron orbitals
σ bonding MO: electron density is shared along the
bonding axis in MO
π bond: side-by-side overlap of unhybridized p orbitals π bonding MO: electron density is shared above and
below the bonding axis in MO
Explains the reactivity of carbon-based molecules
Explains paramagnetic O2
(does NOT explain paramagnetic O2)
Dipoles:
1. Molecular dipoles occur when there is unequal
sharing of electrons between atoms in a molecule.
2. Dipole moments point towards the more electronegative atom.
Polar Bonds:
different electronegativities share electrons unequally and create a
bond dipole
Connections Chemistry Review
October 4, 2021
Hannah Boyce
boyce.h@northeastern.edu
Amanda Dee
Elena Fenstermaker fenstermaker.e@northeastern.edu
Maddie Szoo
Session #4, HW #4
dee.a@northeastern.edu
szoo.m@northeastern.edu
Organic Functional Groups:
Aromatic Hydrocarbons – Have ring structures with unsaturation (multiple bond character) in the alternating
carbon-to-carbon bonds in the ring. Most based on benzene (C6H6)
Ethers – compound with the general formula R-O-R.
Esters – general formula is R1-COO-R2 (water is a product in the formation of an ester from alcohol and
carboxylic acid)
R1
••
••
O
C
••
O
••
R2
Aldehydes/Ketones – contain the carbonyl group which is a C double bonded to an O. In an aldehyde, this
happens on a terminal carbon. In a ketone, this happens on an internal carbon.
(aldehyde)
(ketone)
Amides – contains functional group (-CON-) has general formula R-CONH2
C
H
••
O
••
••
R
••
••
O
N
H
Amines – a derivative of NH3 where one or more H’s may be replaced with R groups.
Thiols – functional group -SH