CEM 141 EXAM 1 REVIEW
QUESTIONS AND ANSWERS 2026
Constructing a Scientific Explanation - ANSWERS1. Claim (target of explanation)
2. Evidence (data used to support)
3. Reasoning (connection between claim and evidence)
Scientific Theory - ANSWERSexplains how/why; best available explanation of existing
evidence; makes testable predictions; is falsifiable; may change over time with new
evidence
Difference Between Law and Theory - ANSWERSLaw: phenomenon; explains WHAT
Theory: tells WHY
How do we know atoms exist? - ANSWERSWe can see them using atomic force
microscopy (AFM) and scanning tunneling microscopy (STM)
What is the difference between an element and a compound? - ANSWERSAn element
is one type of atom vs a compound is several different atoms connected
Atom - ANSWERSis the smallest unit of an element
Dalton's Atomic Theory - ANSWERS1. Elements are composed of small indivisible,
indestructible particles called atoms (NOT TRUE)
2. All atoms of an element are identical and have the same mass and properties (NOT
TRUE)
3. Atoms of a given element are different from atoms of other elements. (TRUE)
4. Compounds are formed by combinations of atoms of 2 or more elements (TRUE)
5. Chemical reactions are due to the rearrangement of atoms, atoms (matter) are
neither created nor destroyed during a reaction (TRUE)
Atomic Theory Development - ANSWERSThe original idea came from the Greeks;
wasn't a scientific theory but philosophy (Ex. Elements=earth, fire, air, water and were
thought to be in constant motion based on watching the movement of specks of dust in
sunlight and that there was nothing between them AKA Brownian Motion)
What distinguishes one element from another? How do atoms of different elements
differ? - ANSWERSDifferent # of protons and atomic symbol
What types of evidence might be used to conclude tat you had isolated a new element?
- ANSWERSWould have new properties
, What types of elements would be difficult to identify? - ANSWERSOnes that aren't
reactive (Ex. Noble gases)
What is the difference between an atom and a molecule? - ANSWERSMolecule:
collection of atoms chemically bonded
Atoms have a subatomic structure - ANSWERSThe electron was discovered first (it was
the easiest to move and detect) by JJ Thompson
Discovery of Electron - ANSWERSCathode ray tube: glass tube consisting of 2
electrodes under very low pressure. When a high voltage is applied, cathode emits
"particles" that move toward anode. Particle rays bend toward positive plate. Therefore
they're negatively charged particles.
Thompson's Atomic Model - ANSWERSPlum Pudding Model
The electromagnetic force is mediated by electric and magnetic fields - ANSWERSall
these forces work at a distance
Electromagnetic force - ANSWERSis much stronger than gravity and can be repulsive
or attractive
Rutherford's Experiment - ANSWERSShot alpha particles through gold foil; some were
deflected and some shot straight through
In Rutherford's experiment, if the atom was like a plum pudding all the alpha particles
should go straight through... - ANSWERSBut a few of the particles did not go through,
most went straight through, and some went through but were deflected. This shows of
that the atom was mostly empty space with a small dense nucleus in the center.
Thompson's Experiment showed... - ANSWERS"particles" emerged from one disc (the
cathode) and moved to the other (the anode); these particles could be deflected by
electrical fields in a direction that would indicate they were negatively charged; the
particles could also be deflected by magnetic fields; the particles carried the electrical
charge—that is if the ray was bent, for example by a magnetic field, the charge went
with it; the metal that the cathode was made of didn't affect the behavior of the ray—so
whatever the composition of the ray—it appeared to be independent of the element that
it came from
What is an alpha particle? - ANSWERSHas 2 protons and 2 neutrons; the nucleus of a
helium atom
Example of inverse square law (as r increases, F decreases by a factor of 1/r^2)
Gravitational Forces are mediated by fields - ANSWERSObjects with mass are sources
of gravitational fields are affected by the gravitational fields of all other objects with
QUESTIONS AND ANSWERS 2026
Constructing a Scientific Explanation - ANSWERS1. Claim (target of explanation)
2. Evidence (data used to support)
3. Reasoning (connection between claim and evidence)
Scientific Theory - ANSWERSexplains how/why; best available explanation of existing
evidence; makes testable predictions; is falsifiable; may change over time with new
evidence
Difference Between Law and Theory - ANSWERSLaw: phenomenon; explains WHAT
Theory: tells WHY
How do we know atoms exist? - ANSWERSWe can see them using atomic force
microscopy (AFM) and scanning tunneling microscopy (STM)
What is the difference between an element and a compound? - ANSWERSAn element
is one type of atom vs a compound is several different atoms connected
Atom - ANSWERSis the smallest unit of an element
Dalton's Atomic Theory - ANSWERS1. Elements are composed of small indivisible,
indestructible particles called atoms (NOT TRUE)
2. All atoms of an element are identical and have the same mass and properties (NOT
TRUE)
3. Atoms of a given element are different from atoms of other elements. (TRUE)
4. Compounds are formed by combinations of atoms of 2 or more elements (TRUE)
5. Chemical reactions are due to the rearrangement of atoms, atoms (matter) are
neither created nor destroyed during a reaction (TRUE)
Atomic Theory Development - ANSWERSThe original idea came from the Greeks;
wasn't a scientific theory but philosophy (Ex. Elements=earth, fire, air, water and were
thought to be in constant motion based on watching the movement of specks of dust in
sunlight and that there was nothing between them AKA Brownian Motion)
What distinguishes one element from another? How do atoms of different elements
differ? - ANSWERSDifferent # of protons and atomic symbol
What types of evidence might be used to conclude tat you had isolated a new element?
- ANSWERSWould have new properties
, What types of elements would be difficult to identify? - ANSWERSOnes that aren't
reactive (Ex. Noble gases)
What is the difference between an atom and a molecule? - ANSWERSMolecule:
collection of atoms chemically bonded
Atoms have a subatomic structure - ANSWERSThe electron was discovered first (it was
the easiest to move and detect) by JJ Thompson
Discovery of Electron - ANSWERSCathode ray tube: glass tube consisting of 2
electrodes under very low pressure. When a high voltage is applied, cathode emits
"particles" that move toward anode. Particle rays bend toward positive plate. Therefore
they're negatively charged particles.
Thompson's Atomic Model - ANSWERSPlum Pudding Model
The electromagnetic force is mediated by electric and magnetic fields - ANSWERSall
these forces work at a distance
Electromagnetic force - ANSWERSis much stronger than gravity and can be repulsive
or attractive
Rutherford's Experiment - ANSWERSShot alpha particles through gold foil; some were
deflected and some shot straight through
In Rutherford's experiment, if the atom was like a plum pudding all the alpha particles
should go straight through... - ANSWERSBut a few of the particles did not go through,
most went straight through, and some went through but were deflected. This shows of
that the atom was mostly empty space with a small dense nucleus in the center.
Thompson's Experiment showed... - ANSWERS"particles" emerged from one disc (the
cathode) and moved to the other (the anode); these particles could be deflected by
electrical fields in a direction that would indicate they were negatively charged; the
particles could also be deflected by magnetic fields; the particles carried the electrical
charge—that is if the ray was bent, for example by a magnetic field, the charge went
with it; the metal that the cathode was made of didn't affect the behavior of the ray—so
whatever the composition of the ray—it appeared to be independent of the element that
it came from
What is an alpha particle? - ANSWERSHas 2 protons and 2 neutrons; the nucleus of a
helium atom
Example of inverse square law (as r increases, F decreases by a factor of 1/r^2)
Gravitational Forces are mediated by fields - ANSWERSObjects with mass are sources
of gravitational fields are affected by the gravitational fields of all other objects with
