CEM 141 CHAPTER 3 TEST
Valence Shell Electron Pair Repulsion (VSEPR) - ANSWERS-1.
helps figure out shape of molecules from Lewis Structure
a. because Lewis Structure shows # of electrons around molecules
b. assume all centers of electron density repel each other
c. there is a minimum energy arrangement that the atom will naturally
make up
2. lone pairs and single, double, and triple bonds (multiple bonds)
each count as 1 center of electron density
a. a single bond is always a sigma bond (allow for free rotation)
b. all the rest are always pi bonds (don't allow for free rotation- it
would break the pi bond)
What is the difference between electron center geometry and
molecular shape? - ANSWERS-1. they are not always the same
a. to determine the shape of a molecule, consider only the atoms, not
the lone pairs
How do you determine the hybridization of a molecule? -
ANSWERS-1. count the number of atoms connected to the central
atom (atoms- not bonds) and count the number of lone pairs attached
to it
a. if its 4: sp^3
b. if its 3: sp^2
c. if its 2: sp
,Electronegativity - ANSWERS-1. ability of an element to attract
electrons to itself in a bond
a. atom with high effective nuclear charge attracts its own valence
electrons strongly and it attracts electrons from other atoms in bonds
2. Depends on effective nuclear charge
3. trend is same as effective nuclear charge (except for noble gases)
a. dec. down a group because atom gets bigger
b. increases across a row because valence electrons are closer to
nucleus
Polar Bonds - ANSWERS-1. when 2 atoms of different
electronegativities bond, the electrons are not shared equally
a. results in a bond dipole (bond is polar)
2. molecular shape is important
a. bond dipoles are vector quantities (have magnitude and direction
that need to be taken into account)
Steps to determine molecular polarity - ANSWERS-1. draw the lewis
structure
2. determine electron center geometry (gives you bond angle and
hybridization)
3. determine molecular shape
4. determine bond polarities
5. add up bond polarities (take direction into account)
6. determine molecular polarity
, Do molecules interact? - ANSWERS-Yes
How do molecules interact? What are the effects of these interactions?
- ANSWERS-1. the stronger the interactions, the higher the MP and
BP
2. Noble Gases. Which has the highest BP?
a. Xe has the highest BP because it has the biggest electron cloud
(bigger partial charges--> bigger LDF to overcome)
Types of Intermolecular Forces (IMFs) - ANSWERS-1. LDFs
2. Dipole-dipole interactions
3. Hydrogen Bonds
LDF - ANSWERS-1. temporary fluctuating dipole
2. depends on size, surface area, and shape of molecule
3. for non-polar molecules, this is the only IMF present
4. present in all substances in liquid and solid states
a. between molecules or individual atoms
Example where LDF is the strongest IMF present - ANSWERS-Non
polar substances, CH4, CO2, hyrdrocarbons, Br2
Dipole-dipole Interactions - ANSWERS-1. present in polar substances
(along with LDF)
Valence Shell Electron Pair Repulsion (VSEPR) - ANSWERS-1.
helps figure out shape of molecules from Lewis Structure
a. because Lewis Structure shows # of electrons around molecules
b. assume all centers of electron density repel each other
c. there is a minimum energy arrangement that the atom will naturally
make up
2. lone pairs and single, double, and triple bonds (multiple bonds)
each count as 1 center of electron density
a. a single bond is always a sigma bond (allow for free rotation)
b. all the rest are always pi bonds (don't allow for free rotation- it
would break the pi bond)
What is the difference between electron center geometry and
molecular shape? - ANSWERS-1. they are not always the same
a. to determine the shape of a molecule, consider only the atoms, not
the lone pairs
How do you determine the hybridization of a molecule? -
ANSWERS-1. count the number of atoms connected to the central
atom (atoms- not bonds) and count the number of lone pairs attached
to it
a. if its 4: sp^3
b. if its 3: sp^2
c. if its 2: sp
,Electronegativity - ANSWERS-1. ability of an element to attract
electrons to itself in a bond
a. atom with high effective nuclear charge attracts its own valence
electrons strongly and it attracts electrons from other atoms in bonds
2. Depends on effective nuclear charge
3. trend is same as effective nuclear charge (except for noble gases)
a. dec. down a group because atom gets bigger
b. increases across a row because valence electrons are closer to
nucleus
Polar Bonds - ANSWERS-1. when 2 atoms of different
electronegativities bond, the electrons are not shared equally
a. results in a bond dipole (bond is polar)
2. molecular shape is important
a. bond dipoles are vector quantities (have magnitude and direction
that need to be taken into account)
Steps to determine molecular polarity - ANSWERS-1. draw the lewis
structure
2. determine electron center geometry (gives you bond angle and
hybridization)
3. determine molecular shape
4. determine bond polarities
5. add up bond polarities (take direction into account)
6. determine molecular polarity
, Do molecules interact? - ANSWERS-Yes
How do molecules interact? What are the effects of these interactions?
- ANSWERS-1. the stronger the interactions, the higher the MP and
BP
2. Noble Gases. Which has the highest BP?
a. Xe has the highest BP because it has the biggest electron cloud
(bigger partial charges--> bigger LDF to overcome)
Types of Intermolecular Forces (IMFs) - ANSWERS-1. LDFs
2. Dipole-dipole interactions
3. Hydrogen Bonds
LDF - ANSWERS-1. temporary fluctuating dipole
2. depends on size, surface area, and shape of molecule
3. for non-polar molecules, this is the only IMF present
4. present in all substances in liquid and solid states
a. between molecules or individual atoms
Example where LDF is the strongest IMF present - ANSWERS-Non
polar substances, CH4, CO2, hyrdrocarbons, Br2
Dipole-dipole Interactions - ANSWERS-1. present in polar substances
(along with LDF)
