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Michigan State University
CEM 141 CEM141 EXAM 1 Questions and
Answers 2026 Latest Update
compound Ans: A molecule is formed when two or more atoms join
together chemically. A compound is a molecule that contains at least two
different elements. All compounds are molecules but not all molecules are
compounds.
Thomson's experiment allowed him to make a claim that 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? Ans: Evidence: Electrons were ejected from the cathode,
regardless of what metal the cathode was made of.
Reasoning: Since the particles are emitted regardless of the nature of the
cathode, they must be part of the sub-structure of the atom.
Atom interactions: True statements Ans: I. All neutral atoms and molecules
attract each other
II. London Dispersion Force increases 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 attract each other.
Rutherford's experiments: Claim, evidence, reasoning? Ans: 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.
© 2026 All rights reserved
, 2 | Page
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? The atomic
theory: Ans: Explains the underlying cause of a range of phenomena.
Law v Theory Ans: A law describes the phenomenon (natural occurrence) A
law tells you what
A theory explains the phenomenon. A theory tells you why
1. A law is an observation; a theory is the explanation of that observation.
2. A theory requires experimentation under various conditions. A law has no
such requirements.
3. A theory may become obsolete with time. This is not the case with a law.
4. A theory can be replaced by another better theory; however, this never
happens with a law.
5. A theory may be strong or weak according to the amount of evidence
available. A law is a universally observable fact.
Which is the smallest? Atom, cell, proton, electron? Ans: Electron
Consider a system where two helium atoms are approaching from a
distance. The distance between the two helium atoms where the system
would be the most stable is: Ans: Where the potential energy is at a
minimum.
Consider a system where two helium atoms are approaching from a
distance. Two atoms approach and get close enough so that their electron
clouds overlap. Why does the potential energy increase? Ans: The electron
clouds repel each other.
What is the cause of the attractive force between the two He atoms? Ans:
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.
Is this statement true or false? Why? Elements are composed of small
indivisible, indestructible particles called atoms. Ans: False; Atoms have
sub-structure
© 2026 All rights reserved
Michigan State University
CEM 141 CEM141 EXAM 1 Questions and
Answers 2026 Latest Update
compound Ans: A molecule is formed when two or more atoms join
together chemically. A compound is a molecule that contains at least two
different elements. All compounds are molecules but not all molecules are
compounds.
Thomson's experiment allowed him to make a claim that 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? Ans: Evidence: Electrons were ejected from the cathode,
regardless of what metal the cathode was made of.
Reasoning: Since the particles are emitted regardless of the nature of the
cathode, they must be part of the sub-structure of the atom.
Atom interactions: True statements Ans: I. All neutral atoms and molecules
attract each other
II. London Dispersion Force increases 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 attract each other.
Rutherford's experiments: Claim, evidence, reasoning? Ans: 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.
© 2026 All rights reserved
, 2 | Page
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? The atomic
theory: Ans: Explains the underlying cause of a range of phenomena.
Law v Theory Ans: A law describes the phenomenon (natural occurrence) A
law tells you what
A theory explains the phenomenon. A theory tells you why
1. A law is an observation; a theory is the explanation of that observation.
2. A theory requires experimentation under various conditions. A law has no
such requirements.
3. A theory may become obsolete with time. This is not the case with a law.
4. A theory can be replaced by another better theory; however, this never
happens with a law.
5. A theory may be strong or weak according to the amount of evidence
available. A law is a universally observable fact.
Which is the smallest? Atom, cell, proton, electron? Ans: Electron
Consider a system where two helium atoms are approaching from a
distance. The distance between the two helium atoms where the system
would be the most stable is: Ans: Where the potential energy is at a
minimum.
Consider a system where two helium atoms are approaching from a
distance. Two atoms approach and get close enough so that their electron
clouds overlap. Why does the potential energy increase? Ans: The electron
clouds repel each other.
What is the cause of the attractive force between the two He atoms? Ans:
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.
Is this statement true or false? Why? Elements are composed of small
indivisible, indestructible particles called atoms. Ans: False; Atoms have
sub-structure
© 2026 All rights reserved
