CEM 141 Exam 1 Questions with Verified Solutions Latest 2025
Atomic hypothesis (Feynman) - Answers All things are made of atoms in perpetual motion; they
attract at moderate distances and repel when squeezed together.
Atom - Answers Smallest particle that retains the identity and properties of an element; mostly
empty space with a dense nucleus and surrounding electrons.
Element - Answers Pure substance defined by a unique number of protons in its atoms' nuclei.
Molecule - Answers Two or more atoms bonded together acting as a unit.
Subatomic particle - Answers Proton (+1, ~1 amu), neutron (0, ~1 amu), electron (-1, ~1/2000
amu).
Quarks and gluons - Answers Constituents of protons and neutrons; held together by the strong
nuclear force.
Electrical neutrality of atoms - Answers In a neutral atom, #protons = #electrons, so net charge
is zero.
Nucleus - Answers Tiny, dense, positively charged center of the atom containing protons and
neutrons.
Electron cloud - Answers Region of space where electrons are found; accounts for most atomic
volume.
Heisenberg uncertainty principle - Answers At atomic scales, measuring a particle perturbs it;
position and momentum cannot both be known exactly.
Wave-particle duality - Answers Electrons, photons, and other quantum entities show both wave-
like and particle-like behavior.
Forces in nature (overview) - Answers Gravity, electromagnetism, strong nuclear, weak nuclear.
Gravity (chemistry context) - Answers Weakest force; negligible for atomic/molecular
interactions.
Electromagnetic force - Answers Attraction/repulsion between charges; dominant force in
chemical behavior.
Strong nuclear force - Answers Very strong, very short-range force that binds protons and
neutrons in the nucleus.
Weak nuclear force - Answers Very short-range force involved in certain radioactive decays.
, Scale of a gold atom - Answers Diameter < 1 nanometer (10⁻⁹ m); nucleus radius ~1.5 × 10⁻¹⁴ m.
Seeing atoms (indirect) - Answers Electron and force-probe microscopes (e.g., STM/AFM)
provide images/computer reconstructions; not visible with light microscopes.
Scientific theory - Answers Well-tested explanatory framework that integrates evidence, makes
predictions, and is revised with new data.
Falsifiability - Answers A scientific idea must be testable in ways that could show it to be false.
Reproducibility - Answers Independent repetition of observations/experiments is required for
acceptance.
Natural vs. supernatural explanations - Answers Science works with observable, measurable
natural phenomena; supernatural claims are outside scientific testing.
Greek atomism (Democritus/Leucippus) - Answers Proposed indivisible "atomos" moving in a
void; different shapes → different properties (insightful but untested).
Four ancient "elements" - Answers Earth, air, fire, water (plus aether in some traditions);
superseded by modern elements.
Alchemy's legacy - Answers Early attempts to understand and manipulate matter; contributed
techniques and isolation of substances (e.g., elements).
Lavoisier's elements (1789) - Answers Listed 33 elements; clarified element vs compound;
helped found modern chemistry.
Phosphorus (Brand) - Answers First element isolated in the modern era (from urine); named
"light-bearer" for its glow.
Mercury from cinnabar - Answers Elemental mercury obtained by roasting the ore cinnabar;
historically used despite toxicity.
Natural vs synthetic elements - Answers ~91 occur naturally; heavier, unstable synthetic
elements made in labs by nuclear reactions.
Evidence for atoms (big picture) - Answers Gas laws, Brownian motion, quantitative
composition, microscopy, and reaction stoichiometry support atomic theory.
Law of multiple proportions - Answers Elements combine in ratios of small whole numbers in
different compounds (Dalton's key evidence).
Dalton's atomic theory (core) - Answers (1) Elements have atoms; (2) atoms of an element are
identical; (3) different elements' atoms differ; (4) compounds are whole-number combinations;
(5) reactions rearrange atoms.
Atomic hypothesis (Feynman) - Answers All things are made of atoms in perpetual motion; they
attract at moderate distances and repel when squeezed together.
Atom - Answers Smallest particle that retains the identity and properties of an element; mostly
empty space with a dense nucleus and surrounding electrons.
Element - Answers Pure substance defined by a unique number of protons in its atoms' nuclei.
Molecule - Answers Two or more atoms bonded together acting as a unit.
Subatomic particle - Answers Proton (+1, ~1 amu), neutron (0, ~1 amu), electron (-1, ~1/2000
amu).
Quarks and gluons - Answers Constituents of protons and neutrons; held together by the strong
nuclear force.
Electrical neutrality of atoms - Answers In a neutral atom, #protons = #electrons, so net charge
is zero.
Nucleus - Answers Tiny, dense, positively charged center of the atom containing protons and
neutrons.
Electron cloud - Answers Region of space where electrons are found; accounts for most atomic
volume.
Heisenberg uncertainty principle - Answers At atomic scales, measuring a particle perturbs it;
position and momentum cannot both be known exactly.
Wave-particle duality - Answers Electrons, photons, and other quantum entities show both wave-
like and particle-like behavior.
Forces in nature (overview) - Answers Gravity, electromagnetism, strong nuclear, weak nuclear.
Gravity (chemistry context) - Answers Weakest force; negligible for atomic/molecular
interactions.
Electromagnetic force - Answers Attraction/repulsion between charges; dominant force in
chemical behavior.
Strong nuclear force - Answers Very strong, very short-range force that binds protons and
neutrons in the nucleus.
Weak nuclear force - Answers Very short-range force involved in certain radioactive decays.
, Scale of a gold atom - Answers Diameter < 1 nanometer (10⁻⁹ m); nucleus radius ~1.5 × 10⁻¹⁴ m.
Seeing atoms (indirect) - Answers Electron and force-probe microscopes (e.g., STM/AFM)
provide images/computer reconstructions; not visible with light microscopes.
Scientific theory - Answers Well-tested explanatory framework that integrates evidence, makes
predictions, and is revised with new data.
Falsifiability - Answers A scientific idea must be testable in ways that could show it to be false.
Reproducibility - Answers Independent repetition of observations/experiments is required for
acceptance.
Natural vs. supernatural explanations - Answers Science works with observable, measurable
natural phenomena; supernatural claims are outside scientific testing.
Greek atomism (Democritus/Leucippus) - Answers Proposed indivisible "atomos" moving in a
void; different shapes → different properties (insightful but untested).
Four ancient "elements" - Answers Earth, air, fire, water (plus aether in some traditions);
superseded by modern elements.
Alchemy's legacy - Answers Early attempts to understand and manipulate matter; contributed
techniques and isolation of substances (e.g., elements).
Lavoisier's elements (1789) - Answers Listed 33 elements; clarified element vs compound;
helped found modern chemistry.
Phosphorus (Brand) - Answers First element isolated in the modern era (from urine); named
"light-bearer" for its glow.
Mercury from cinnabar - Answers Elemental mercury obtained by roasting the ore cinnabar;
historically used despite toxicity.
Natural vs synthetic elements - Answers ~91 occur naturally; heavier, unstable synthetic
elements made in labs by nuclear reactions.
Evidence for atoms (big picture) - Answers Gas laws, Brownian motion, quantitative
composition, microscopy, and reaction stoichiometry support atomic theory.
Law of multiple proportions - Answers Elements combine in ratios of small whole numbers in
different compounds (Dalton's key evidence).
Dalton's atomic theory (core) - Answers (1) Elements have atoms; (2) atoms of an element are
identical; (3) different elements' atoms differ; (4) compounds are whole-number combinations;
(5) reactions rearrange atoms.
