MEASUREMENT UNCERTAINTY AND ACCURACY
Which describes measurements that are close to the true value?
A. Accuracy
B. Precision
C. Density
D. Resolution
A. Accuracy
A sample of metal has a mass of 80 g and a volume of 20 cm³. What is its density?
A. 2 g/cm³
B. 3 g/cm³
C. 4 g/cm³
D. 5 g/cm³
C. 4 g/cm³
Which Greek philosopher proposed that matter is made of tiny, indivisible particles called atomos?
A. Aristotle
B. Democritus
C. Thales
D. Heraclitus
B. Democritus
According to Bohr's atomic model, electrons move around the nucleus in __________.
A. fixed energy levels
B. random nuclear paths
C. continuous energy clouds
D. overlapping proton shells
A. fixed energy levels
Which quantum number identifies the main energy level occupied by an electron?
A. Principal quantum number
B. Angular momentum quantum number
C. Magnetic quantum number
D. Spin quantum number
A. Principal quantum number
Which situation is the best example of a systematic error?
A. A balance gives readings that vary slightly each trial.
B. A ruler has faded markings that are difficult to read.
C. A thermometer is improperly calibrated by +2°C.
D. A student estimates the last digit differently each time.
C. A thermometer is improperly calibrated by +2°C.
Which observation represents a chemical property of iron?
A. Iron has a gray and shiny surface.
B. Iron conducts heat through its structure.
C. Iron reacts with oxygen to form rust.
D. Iron can be shaped into thin sheets.
C. Iron reacts with oxygen to form rust.
What major discovery caused scientists to revise John Dalton's idea of an indivisible atom?
A. Atoms were found to contain smaller subatomic particles.
B. Elements were found to exist in different physical states.
C. Compounds were found to contain two or more elements.
D. Matter was found to undergo physical and chemical changes.
A. Atoms were found to contain smaller subatomic particles.
What happens when an electron absorbs a specific amount of energy in Bohr's model?
A. It moves to a higher energy level.
B. It combines directly with the nucleus.
C. It loses its negative electrical charge.
D. It changes permanently into another particle.
A. It moves to a higher energy level.
What is the maximum number of electrons that can occupy one orbital?
A. One electron with any spin
B. Two electrons with opposite spins
C. Four electrons with paired spins
D. Eight electrons with opposite spins
B. Two electrons with opposite spins
Which value has four significant figures?
A. 0.0056
B. 5.60
C. 560
D. 0.0560
D. 0.0560
Two cubes are made of the same pure copper. One cube is twice as large as the other. Which statement is correct?
A. The larger cube has a higher density.
B. The smaller cube has a higher density.
C. Both cubes have the same density.
D. Both cubes have different specific gravities.
C. Both cubes have the same density.
J. J. Thomson's cathode ray experiment provided evidence for which idea?
A. Atoms contain negatively charged particles called electrons.
B. Atoms contain dense nuclei surrounded by empty space.
C. Electrons move around nuclei in fixed energy levels.
D. Matter consists only of earth, water, air, and fire.
A. Atoms contain negatively charged particles called electrons.
An electron moves from n=2 to n=4. What occurred?
A. A neutron was lost
B. Energy was released
C. A proton was gained
D. Energy was absorbed
D. Energy was absorbed
A student writes the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁷. Why is this configuration invalid?
A. The third energy level cannot contain any p subshell.
B. A p subshell can accommodate a maximum of six electrons.
C. The 3s subshell must contain six electrons before filling 3p.
D. Electrons cannot occupy the third energy level in ground-state atoms.
B. A p subshell can accommodate a maximum of six electrons.
Which data set is both accurate and precise if the true mass is 25.00 g?
A. 24.10, 24.09, 24.11
B. 25.00, 25.01, 24.99
C. 24.80, 25.20, 25.00
D. 26.00, 25.00, 24.00
B. 25.00, 25.01, 24.99
Two solid blocks have identical volumes but different masses. Block X has twice the mass of Block Y. What can be inferred?
A. Block X has twice the density of Block Y.
B. Block Y has twice the density of Block X.
C. Both blocks have equal densities due to equal volumes.
D. Their densities cannot be compared without knowing temperature.
A. Block X has twice the density of Block Y.
In Rutherford's experiment, most alpha particles passed directly through the gold foil, while a few were strongly deflected. What conclusion best explains both observations?
A. Atoms are solid spheres containing evenly distributed positive charges.
B. Atoms are mostly empty space with a small, dense, positive nucleus.
C. Electrons occupy fixed energy levels surrounding a negatively charged nucleus.
D. Positive and negative charges are uniformly distributed throughout the atom.
B. Atoms are mostly empty space with a small, dense, positive nucleus.
An excited electron returns from a higher energy level to a lower energy level. Which event should occur?
A. Energy is absorbed as the electron approaches the nucleus.
B. Energy is emitted as the electron moves to a lower state.
C. The electron gains mass because its energy level decreases.
D. The nucleus releases a proton to maintain atomic stability.
B. Energy is emitted as the electron moves to a lower state.
An electron has the quantum numbers n = 3 and ℓ = 2. In which subshell is the electron located?
A. 3s subshell
B. 3p subshell
C. 3d subshell
D. 3f subshell
C. 3d subshell
A student obtained the following measurements for a 50.00 g standard: 49.99 g, 50.00 g, and 50.01 g. Another student obtained 50.60 g, 50.60 g, and 50.60 g. Which student collected more reliable data?
A. Student 1 because the measurements are both accurate and precise.
B. Student 2 because identical measurements indicate perfect accuracy.
C. Student 2 because precision is more important than accuracy.
D. Both students collected equally reliable measurements.
A. Student 1 because the measurements are both accurate and precise.
A scientist needs to identify an unknown pure substance without changing its chemical composition. Which combination of tests would be most useful?
A. Mass and volume because both are extensive properties.
B. Weight and length because both identify the particles present.
C. Shape and size because both remain constant for every sample.
D. Density and melting point because both are characteristic properties.
D. Density and melting point because both are characteristic properties.
Suppose every alpha particle in Rutherford's experiment had bounced backward. Which atomic structure would best explain this hypothetical observation?
A. An atom consisting mainly of empty space around a tiny nucleus.
B. An atom containing diffuse positive charge throughout a large volume.
C. An atom consisting of highly concentrated matter blocking most particles.
D. An atom containing electrons arranged within several fixed energy levels.
C. An atom consisting of highly concentrated matter blocking most particles.
A student draws electrons traveling in exact circular paths around the nucleus and labels the diagram as a quantum mechanical model. What is the best evaluation of the diagram?
A. Correct, because quantum mechanics predicts exact electron paths around nuclei.
B. Correct, because orbitals and circular paths represent exactly the same concept.
C. Incorrect, because the quantum model describes probable electron locations using orbitals.
D. Incorrect, because quantum mechanics places all electrons directly inside the atomic nucleus.
C. Incorrect, because the quantum model describes probable electron locations using orbitals.
Which set of quantum numbers is valid?
A. n=3, ℓ=3, mℓ=0, ms=+1/2
B. n=2, ℓ=1, mℓ=2, ms=−1/2
C. n=4, ℓ=2, mℓ=−2, ms=+1/2
D. n=3, ℓ=2, mℓ=1, ms=+1
C. n=4, ℓ=2, mℓ=−2, ms=+1/2