CEM 141 FINAL EXAM QUESTIONS
AND ANSWERS
What is the best explanation for a pattern such as those obtained when X-Rays are
diffracted by crystals? - Answer- The waves of electromagnetic radiation arrive in-phase
and out-of-phase at the detector.
Consider the isoelectronic (they all have the same number of electrons) species Na+,
Mg2+, Ne, and F-, which of these has the smallest radius? - Answer- Mg2+
-Has the highest proton to electron ratio, therefore highest ENC and strongest
attraction, which pulls the electrons toward the nucleus.
When and where were the carbon and oxygen atoms in your body created? - Answer-
Within stars and stellar explosions
Thomson observed that the type of metal used for the cathode did not affect the
behavior of the cathode ray. What claim does this piece of evidence support? - Answer-
All atoms contain electrons
Consider a container of xenon atoms where two xenon atoms of interest are interacting
(the system) and are surrounded by other xenon atoms. The surrounding xenon atoms
have more energy than the two xenon atoms in the system. Which direction would you
predict the energy would be transferred and what would happen? - Answer- During a
collision energy will be transferred from the surrounding xenon atoms to the system of
two xenon atoms, and the stable interaction will be overcome.
How would the strength of the electrostatic force change if the distance between two
charged objects increased? - Answer- The electrostatic force would become weaker.
Does one molecule of water have a boiling point? Why or why not? - Answer- NO
The boiling point is the temperature at which the particles change from liquid to gas. If
there is only one particle the words liquid and gas (and solid or that matter) are
meaningless.
Why are metals shiny? - Answer- Because they absorb photons and re-emit them.
-
Metals have molecular orbitals that are very close together in energy. They can absorb
almost any wavelength of light because the gap between the levels is negligible. The
absorbed light can then be re-emitted.
, Thomson's experiment allowed him to make the claim that all atoms have a sub
structure and contain smaller particles (electrons) embedded in the structure of the
atom. What evidence and reasoning allowed him to make this claim? - Answer-
Evidence: i. Electrons were ejected from the cathode, regardless of what metal the
cathode was made of.
Reasoning: iii. Since the particles are emitted regardless of the nature of the cathode,
they must be part of the sub-structure of the atom.
Which of these statements are true:
i. All neutral atoms and molecules attract eachother.
ii. London Dispersion Forces increase as the size of the electron cloud increases.
iii. It takes energy to overcome the attractions between particles.
iv. Energy is released to the surroundings when atoms form a stable interaction. -
Answer- ALL ARE TRUE
The atomic theory of matter is an example of a scientific theory. What distinguishes it
from a scientific law such as the law of gravity? - Answer- The atomic theory explains
the underlying cause of a range of phenomena.
Best set of claim, evidence, and reasoning that can be used to explain the results of
Rutherford's experiments. - Answer- CLAIM: The atom is mostly empty space with a
very small dense nucleus.
EVIDENCE: Most alpha particles went straight through, only a few were deflected.
REASONING: The positively charged alpha particles were deflected by the repulsive
interaction with the positive nucleus; since only a few were deflected the nucleus must
take up a very small volume of the atom.
Which is smallest? An atom, a cell, a proton, or an electron. - Answer- An electron
The distance between the two helium atoms where the system would be the most stable
is... - Answer- where the potential energy is at a minimum.
Two atoms approach and get close enough so that their electron clouds overlap. Why
does the potential energy increase? - Answer- The electron clouds repel eachother.
What is the cause of the attractive force between two He atoms? - Answer- The electron
clouds of the He atoms may fluctuate randomly causing a transient dipole that induces a
dipole in other atoms which causes them to attract to each other.
As two positively charged objects approach each other, what happens to the potential
energy of a system? - Answer- INCREASES
Is this statement (one of Dalton's atomic theory tenets) true or false and why?
"Elements are composed of small indivisible, indestructible particles called atoms." -
Answer- FALSE
Atoms have a sub-structure
AND ANSWERS
What is the best explanation for a pattern such as those obtained when X-Rays are
diffracted by crystals? - Answer- The waves of electromagnetic radiation arrive in-phase
and out-of-phase at the detector.
Consider the isoelectronic (they all have the same number of electrons) species Na+,
Mg2+, Ne, and F-, which of these has the smallest radius? - Answer- Mg2+
-Has the highest proton to electron ratio, therefore highest ENC and strongest
attraction, which pulls the electrons toward the nucleus.
When and where were the carbon and oxygen atoms in your body created? - Answer-
Within stars and stellar explosions
Thomson observed that the type of metal used for the cathode did not affect the
behavior of the cathode ray. What claim does this piece of evidence support? - Answer-
All atoms contain electrons
Consider a container of xenon atoms where two xenon atoms of interest are interacting
(the system) and are surrounded by other xenon atoms. The surrounding xenon atoms
have more energy than the two xenon atoms in the system. Which direction would you
predict the energy would be transferred and what would happen? - Answer- During a
collision energy will be transferred from the surrounding xenon atoms to the system of
two xenon atoms, and the stable interaction will be overcome.
How would the strength of the electrostatic force change if the distance between two
charged objects increased? - Answer- The electrostatic force would become weaker.
Does one molecule of water have a boiling point? Why or why not? - Answer- NO
The boiling point is the temperature at which the particles change from liquid to gas. If
there is only one particle the words liquid and gas (and solid or that matter) are
meaningless.
Why are metals shiny? - Answer- Because they absorb photons and re-emit them.
-
Metals have molecular orbitals that are very close together in energy. They can absorb
almost any wavelength of light because the gap between the levels is negligible. The
absorbed light can then be re-emitted.
, Thomson's experiment allowed him to make the claim that all atoms have a sub
structure and contain smaller particles (electrons) embedded in the structure of the
atom. What evidence and reasoning allowed him to make this claim? - Answer-
Evidence: i. Electrons were ejected from the cathode, regardless of what metal the
cathode was made of.
Reasoning: iii. Since the particles are emitted regardless of the nature of the cathode,
they must be part of the sub-structure of the atom.
Which of these statements are true:
i. All neutral atoms and molecules attract eachother.
ii. London Dispersion Forces increase as the size of the electron cloud increases.
iii. It takes energy to overcome the attractions between particles.
iv. Energy is released to the surroundings when atoms form a stable interaction. -
Answer- ALL ARE TRUE
The atomic theory of matter is an example of a scientific theory. What distinguishes it
from a scientific law such as the law of gravity? - Answer- The atomic theory explains
the underlying cause of a range of phenomena.
Best set of claim, evidence, and reasoning that can be used to explain the results of
Rutherford's experiments. - Answer- CLAIM: The atom is mostly empty space with a
very small dense nucleus.
EVIDENCE: Most alpha particles went straight through, only a few were deflected.
REASONING: The positively charged alpha particles were deflected by the repulsive
interaction with the positive nucleus; since only a few were deflected the nucleus must
take up a very small volume of the atom.
Which is smallest? An atom, a cell, a proton, or an electron. - Answer- An electron
The distance between the two helium atoms where the system would be the most stable
is... - Answer- where the potential energy is at a minimum.
Two atoms approach and get close enough so that their electron clouds overlap. Why
does the potential energy increase? - Answer- The electron clouds repel eachother.
What is the cause of the attractive force between two He atoms? - Answer- The electron
clouds of the He atoms may fluctuate randomly causing a transient dipole that induces a
dipole in other atoms which causes them to attract to each other.
As two positively charged objects approach each other, what happens to the potential
energy of a system? - Answer- INCREASES
Is this statement (one of Dalton's atomic theory tenets) true or false and why?
"Elements are composed of small indivisible, indestructible particles called atoms." -
Answer- FALSE
Atoms have a sub-structure
