CEM 141 EXAM 3 QUESTIONS
AND ANSWERS
Describe the structure of ionic compounds. Use the structure to explain the properties of
ionic compounds (ex: melting point, boiling point, hardness, and ability to conduct
electricity). Predict and/or rank relative melting and boiling points of given compounds. -
Answer-Ionic compounds contain one nonmetal and one metal. They generally have
high boiling points because lots of energy is required to break the ion-ion interactions.
Explain differences in melting and boiling points in terms of forces and energy. -
Answer-LDFs < dipole-dipole < hydrogen bonding < ionic bonding < covalent bonding
Draw structural isomers when given a molecular formula. Distinguish between structural
isomers and alternative representations of the same molecule. - Answer-isomers: differ
in connectivity between atoms and properties, but still have the same number of atoms
and chemical formula
Explain why rotation is (generally) easy around a sigma (single) bond, but more difficult
around pi bonds. - Answer-rotation is restricted around the pi bond because if atoms
bonded by a pi bonds were rotated relative to each other, the bond would break
because pi bonds are bonded side to side. Sigma bonds, however, are bonded end to
end, so rotation around a sigma bond is generally easy.
Use Lewis structures and VSEPR to deduce electron pair geometry and molecular
shape of molecules. - Answer-study VSEPR
Predict, draw models (pictures), and explain why relative melting points and boiling
points for substances that exist as molecules (like H2) differ from those that exist as
continuous extended networks (like diamond or metals). - Answer-discrete atoms: lower
melting/boiling points, are not diatomic
small molecules: lower melting/boiling points, diatomic, lower because are only held
together by LDFs, which are substantially weaker than continuous extended networks
continuous extended networks: higher melting/boiling points, higher because covalent
bonds have to be broken in order to turn solids to liquids, liquids to gas
Compare and contrast the molecular orbital bond model and the valence bond model.
What are the similarities/differences? - Answer-molecular orbital bond model: atomic
orbitals combine to form an equal number of molecular orbitals, each orbital can contain
AND ANSWERS
Describe the structure of ionic compounds. Use the structure to explain the properties of
ionic compounds (ex: melting point, boiling point, hardness, and ability to conduct
electricity). Predict and/or rank relative melting and boiling points of given compounds. -
Answer-Ionic compounds contain one nonmetal and one metal. They generally have
high boiling points because lots of energy is required to break the ion-ion interactions.
Explain differences in melting and boiling points in terms of forces and energy. -
Answer-LDFs < dipole-dipole < hydrogen bonding < ionic bonding < covalent bonding
Draw structural isomers when given a molecular formula. Distinguish between structural
isomers and alternative representations of the same molecule. - Answer-isomers: differ
in connectivity between atoms and properties, but still have the same number of atoms
and chemical formula
Explain why rotation is (generally) easy around a sigma (single) bond, but more difficult
around pi bonds. - Answer-rotation is restricted around the pi bond because if atoms
bonded by a pi bonds were rotated relative to each other, the bond would break
because pi bonds are bonded side to side. Sigma bonds, however, are bonded end to
end, so rotation around a sigma bond is generally easy.
Use Lewis structures and VSEPR to deduce electron pair geometry and molecular
shape of molecules. - Answer-study VSEPR
Predict, draw models (pictures), and explain why relative melting points and boiling
points for substances that exist as molecules (like H2) differ from those that exist as
continuous extended networks (like diamond or metals). - Answer-discrete atoms: lower
melting/boiling points, are not diatomic
small molecules: lower melting/boiling points, diatomic, lower because are only held
together by LDFs, which are substantially weaker than continuous extended networks
continuous extended networks: higher melting/boiling points, higher because covalent
bonds have to be broken in order to turn solids to liquids, liquids to gas
Compare and contrast the molecular orbital bond model and the valence bond model.
What are the similarities/differences? - Answer-molecular orbital bond model: atomic
orbitals combine to form an equal number of molecular orbitals, each orbital can contain
