CEM 141 FINAL EXAM QUESTIONS AND
ANSWERS WITH SOLUTIONS 2024
Why are alpha particles deflected by the nucleus? - ANSWER Because both the alpha particles and the
nucleus are positively charged and so the alpha particle is repelled.
Is this statement (Dalton's Theory) true or false and why?
"All atoms of an element are identical and have the same mass and properties." - ANSWER False.
Atoms of the same element can have different numbers of neutrons.
What is the evidence that electrons are subatomic particles? - ANSWER The nature of the electron is
independent of the material from which it emerges.
Example of a theory (explains) - ANSWER The properties of matter can be EXPLAINED by understanding
that matter is composed of atoms that interact and move in various predictable ways.
Why is the boiling point of iodine higher than that of bromine? - ANSWER Because iodine has a larger
more polarizable electron cloud. The electrostatic attraction between the iodine molecules requires
more energy to overcome.
When bromine melts, what is happening? - ANSWER Attractive forces between molecules are overcome.
When oxygen freezes, what is happening with the forces and energy changes during this process? -
ANSWER New LDFs are formed. Energy is released to the surroundings. Energy is transferred via
collisions.
Where would two atoms of He be most stable on a PE curve? - ANSWER The PE well, where the
attractive and repulsive forces are equal and the system is most stable.
For a pencil sitting on a desk, what forces are acting upon the pencil? - ANSWER Both gravitational and
electrostatic.
, If the PE increases as two particles approach, what are they most likely? - ANSWER Two protons
(positively charged/same charge).
How do atoms know that temperature is increasing? - ANSWER Thermal energy is transferred upon
collision with other atoms.
What two atoms would have the greatest gravitational forces? Two 10g separated by 10 meters. Or, one
100g and one 1g separated by 5 meters?
m1m2/r^2 - ANSWER 100g and 1g separated by 5 meters.
(100)(1)/(25) = 4
In the solid state, atoms of xenon are held together by.. - ANSWER London Dispersion Forces ONLY
because Xenon is a noble gas that cannot bond together.
What does a lower PE well mean?
What does a further right position on the PE graph mean? - ANSWER More energy needed to break
interactions.
Longer bond.
What is true about the PE minimum for the approach of two atoms? - ANSWER The depth of the well
tells you how much energy is required to break an interaction.
In breaking a single chemical bond.. - ANSWER Energy is RELEASED.
As two atoms approach each other why does the PE decrease? - ANSWER Because there is an attractive
force between the two atoms.
What does not have atoms in it? - ANSWER Light and heat.
What subatomic particle was discovered last? - ANSWER The neutron because it has no charge and is
therefore difficult to detect.
ANSWERS WITH SOLUTIONS 2024
Why are alpha particles deflected by the nucleus? - ANSWER Because both the alpha particles and the
nucleus are positively charged and so the alpha particle is repelled.
Is this statement (Dalton's Theory) true or false and why?
"All atoms of an element are identical and have the same mass and properties." - ANSWER False.
Atoms of the same element can have different numbers of neutrons.
What is the evidence that electrons are subatomic particles? - ANSWER The nature of the electron is
independent of the material from which it emerges.
Example of a theory (explains) - ANSWER The properties of matter can be EXPLAINED by understanding
that matter is composed of atoms that interact and move in various predictable ways.
Why is the boiling point of iodine higher than that of bromine? - ANSWER Because iodine has a larger
more polarizable electron cloud. The electrostatic attraction between the iodine molecules requires
more energy to overcome.
When bromine melts, what is happening? - ANSWER Attractive forces between molecules are overcome.
When oxygen freezes, what is happening with the forces and energy changes during this process? -
ANSWER New LDFs are formed. Energy is released to the surroundings. Energy is transferred via
collisions.
Where would two atoms of He be most stable on a PE curve? - ANSWER The PE well, where the
attractive and repulsive forces are equal and the system is most stable.
For a pencil sitting on a desk, what forces are acting upon the pencil? - ANSWER Both gravitational and
electrostatic.
, If the PE increases as two particles approach, what are they most likely? - ANSWER Two protons
(positively charged/same charge).
How do atoms know that temperature is increasing? - ANSWER Thermal energy is transferred upon
collision with other atoms.
What two atoms would have the greatest gravitational forces? Two 10g separated by 10 meters. Or, one
100g and one 1g separated by 5 meters?
m1m2/r^2 - ANSWER 100g and 1g separated by 5 meters.
(100)(1)/(25) = 4
In the solid state, atoms of xenon are held together by.. - ANSWER London Dispersion Forces ONLY
because Xenon is a noble gas that cannot bond together.
What does a lower PE well mean?
What does a further right position on the PE graph mean? - ANSWER More energy needed to break
interactions.
Longer bond.
What is true about the PE minimum for the approach of two atoms? - ANSWER The depth of the well
tells you how much energy is required to break an interaction.
In breaking a single chemical bond.. - ANSWER Energy is RELEASED.
As two atoms approach each other why does the PE decrease? - ANSWER Because there is an attractive
force between the two atoms.
What does not have atoms in it? - ANSWER Light and heat.
What subatomic particle was discovered last? - ANSWER The neutron because it has no charge and is
therefore difficult to detect.
