Quiz: Chemistry Matter and Atomic Structure — 24 questions

1. Which classification describes matter that has a fixed composition?

A. A variable solution

B. A pure substance

C. A heterogeneous mixture

D. A homogeneous mixture

Answer: (B)

Explanation

A pure substance has a fixed composition, while a mixture combines substances and may have variable composition. A homogeneous mixture can appear uniform but still contains more than one substance.

2. What distinguishes an element from a compound?

A. An element is physically combined, whereas a compound is separated by filtration.

B. An element contains one type of atom, whereas a compound contains chemically bonded elements.

C. An element has a variable composition, whereas a compound has distinguishable phases.

D. An element contains several bonded atoms, whereas a compound contains one type of atom.

Answer: (B)

Explanation

An element consists of one type of atom, while a compound contains two or more elements chemically joined. The alternative descriptions confuse atomic identity with physical mixtures or separation methods.

3. Which substance is classified as a compound because it contains chemically joined elements?

A. Au

B. Fe

C. NaCl

D. O₂

Answer: (C)

Explanation

NaCl contains sodium and chlorine chemically joined, so it is a compound. Au, O₂, and Fe each contain one type of atom and therefore represent elements.

4. A sample contains visibly different regions with different compositions. How should it be classified?

A. As a homogeneous mixture

B. As a heterogeneous mixture

C. As an individual element

D. As a pure compound

Answer: (B)

Explanation

A heterogeneous mixture has distinguishable components or phases, matching the visibly different regions in the sample. A homogeneous mixture has uniform composition, while a pure compound or element has a fixed chemical identity.

5. Which statement correctly compares a liquid with a gas?

A. A liquid contains charged particles, whereas a gas contains neutral particles.

B. A liquid has defined volume, whereas a gas does not.

C. A liquid has defined shape, whereas a gas has defined volume.

D. A liquid has widely separated particles, whereas a gas has packed particles.

Answer: (B)

Explanation

A liquid maintains a defined volume but takes the shape of its container, while a gas has neither defined shape nor defined volume. Particle spacing and electrical charge do not provide the stated distinction between ordinary liquids and gases.

6. Which phase change is endothermic?

A. Melting

B. Freezing

C. Solidification

D. Condensation

Answer: (A)

Explanation

Melting absorbs heat as a solid becomes a liquid, making it endothermic. Condensation, solidification, and freezing release heat because they move toward more ordered phases.

7. In a solution, what is the role of the solvent?

A. It determines whether the mixture is heterogeneous.

B. It is the substance being dissolved.

C. It dissolves the solute.

D. It forms a new element with the solute.

Answer: (C)

Explanation

The solvent is the component that dissolves the solute in a solution. The substance being dissolved is the solute, and dissolving does not create a new element or necessarily produce a heterogeneous mixture.

8. Which solution contains more dissolved solute than the saturated amount under the same reference conditions?

A. A concentrated solution

B. A dilute solution

C. A supersaturated solution

D. A saturated solution

Answer: (C)

Explanation

A supersaturated solution contains more dissolved solute than a saturated solution can normally hold under the same conditions. A concentrated solution contains a relatively large amount of solute but does not necessarily exceed the saturation limit.

9. What does concentration describe in a solution?

A. The chemical identity of every atom in the solute

B. The temperature at which the solvent changes phase

C. The total number of phases visible in the solution

D. The amount of solute dissolved in a specific amount of solvent

Answer: (D)

Explanation

Concentration measures how much solute is dissolved in a specified amount of solvent. It does not describe the number of visible phases, a phase-change temperature, or the complete atomic identity of the solute.

10. A solution contains 5 grams of solute and 95 grams of solvent. What is its mass/mass percentage?

A. 5% m/m

B. 5.3% m/m

C. 95% m/m

D. 19% m/m

Answer: (A)

Explanation

The solution mass is $5+95=100$ grams, so $$. Dividing by the solvent mass would not use the required mass of the complete solution.

11. Which sequence correctly describes the historical development of atomic models from earliest to most recent?

A. Thomson, Dalton, Democritus, Bohr, Rutherford, Schrödinger

B. Dalton, Democritus, Rutherford, Thomson, Schrödinger, Bohr

C. Democritus, Dalton, Thomson, Rutherford, Bohr, Schrödinger

D. Democritus, Thomson, Dalton, Rutherford, Schrödinger, Bohr

Answer: (C)

Explanation

The models progressed from Democritus’s atoms through Dalton’s solid spheres, Thomson’s electrons, Rutherford’s nucleus, Bohr’s energy levels, and Schrödinger’s orbitals. Rutherford introduced the nucleus, while Bohr explained electron energy levels.

12. Which statement correctly distinguishes wavelength from frequency in light?

A. Wavelength is the spatial period of a wave, whereas frequency is its oscillation rate.

B. Wavelength measures brightness, whereas frequency measures the wave’s travel distance.

C. Wavelength identifies energy level, whereas frequency identifies the atomic nucleus.

D. Wavelength is the oscillation rate of a wave, whereas frequency is its spatial period.

Answer: (A)

Explanation

Wavelength describes the distance over which a wave pattern repeats, while frequency describes how rapidly it oscillates. Brightness and atomic structure are different properties and do not define these two wave quantities.

13. A light wave in vacuum has wavelength $6.0 \times 10^{-7}\ \text{m}$ and frequency $5.0 \times 10^{14}\ \text{Hz}$. Which relationship correctly gives its speed?

A. $c = \lambda\nu = 3.0 \times 10^{8}\ \text{m/s}$

B. $c = \frac{\nu}{\lambda} = 8.3 \times 10^{20}\ \text{m/s}$

C. $c = \lambda + \nu = 5.0 \times 10^{14}\ \text{m/s}$

D. $c = \lambda - \nu = -5.0 \times 10^{14}\ \text{m/s}$

Answer: (A)

Explanation

For light in vacuum, speed is calculated with $c = \lambda\nu$, giving $\left(6.0 \times 10^{-7}\right)\left(5.0 \times 10^{14}\right)=3.0 \times 10^{8}\ \text{m/s}$. Adding or subtracting wavelength and frequency does not represent the wave-speed relationship.

14. An atom has mass number $A=23$ and atomic number $Z=11$. How many neutrons does its nucleus contain?

A. 12 neutrons

B. 34 neutrons

C. 23 neutrons

D. 11 neutrons

Answer: (A)

Explanation

The neutron number is found from $n=A-Z$, so $n=23-11=12$. The atomic number gives the proton count, while the mass number includes both protons and neutrons.

15. What does the atomic number $Z$ identify?

A. The number of protons in the nucleus

B. The total number of protons and neutrons

C. The number of electrons in every form of the atom

D. The number of neutrons in the nucleus

Answer: (A)

Explanation

Atomic number $Z$ is defined as the number of protons in the nucleus and determines the element’s identity. The total of protons and neutrons is the mass number $A$.

16. What change occurs when a neutral atom becomes an anion?

A. It loses neutrons and has fewer neutrons than protons.

B. It gains protons and has more protons than electrons.

C. It loses electrons and has fewer electrons than protons.

D. It gains electrons and has more electrons than protons.

Answer: (D)

Explanation

An anion forms when a neutral atom gains electrons, producing more electrons than protons. Losing electrons instead forms a cation, while changes in protons or neutrons do not define an anion.

17. Which sublevel corresponds to a secondary quantum number of $l=2$?

A. The s sublevel

B. The f sublevel

C. The p sublevel

D. The d sublevel

Answer: (D)

Explanation

The secondary quantum number maps as $l=0$ to s, $l=1$ to p, $l=2$ to d, and $l=3$ to f. Therefore, $l=2$ identifies a d sublevel.

18. What does an electron configuration describe?

A. How neutrons determine the mass number

B. How electrons are arranged in an atom

C. How protons are counted in the nucleus

D. How light wavelengths are absorbed by an atom

Answer: (B)

Explanation

Electron configuration represents the arrangement of an atom’s electrons among orbitals and energy levels. Proton counting gives the atomic number, while neutron counting contributes to the mass number.

19. Which statement correctly combines the Aufbau, Hund, and Pauli principles?

A. Aufbau fills lower-energy orbitals first, Hund separates equivalent-orbital electrons before pairing, and Pauli permits two opposite-spin electrons per orbital.

B. Aufbau fills orbitals randomly, Hund pairs electrons before separation, and Pauli permits two electrons with matching spins per orbital.

C. Aufbau pairs equivalent-orbital electrons first, Hund fills higher-energy orbitals first, and Pauli permits three electrons per orbital.

D. Aufbau assigns opposite spins, Hund limits each orbital to two electrons, and Pauli places electrons in separate equivalent orbitals.

Answer: (A)

Explanation

Aufbau determines the energy-based filling order, Hund’s rule favors separate occupation of equivalent orbitals before pairing, and Pauli limits an orbital to two opposite-spin electrons. The other descriptions interchange these rules or violate the two-electron limit.

20. Which orbital sequence follows the stated electron-filling order through the first four sublevels of the third shell?

A. $1s \rightarrow 2s \rightarrow 3s \rightarrow 2p \rightarrow 4s \rightarrow 3p \rightarrow 3d$

B. $1s \rightarrow 2p \rightarrow 2s \rightarrow 3s \rightarrow 3p \rightarrow 3d \rightarrow 4s$

C. $1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 4s \rightarrow 3p \rightarrow 3d$

D. $1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$

Answer: (D)

Explanation

The stated sequence begins $1s, 2s, 2p, 3s, 3p, 4s, 3d$, so the first option preserves the required order. In particular, $3p$ is filled before $4s$, and $4s$ precedes $3d$.

21. How are groups and periods arranged in the periodic table?

A. Groups are columns, and periods are rows

B. Groups are blocks, and periods are diagonal sets

C. Groups are diagonal sets, and periods are blocks

D. Groups are rows, and periods are columns

Answer: (A)

Explanation

The periodic table has 18 groups arranged vertically as columns and 7 periods arranged horizontally as rows. Confusing groups with rows reverses these two organizational directions.

22. What does ionization energy measure?

A. The energy released when an atom gains a proton

B. The tendency of a nucleus to repel electrons

C. The tendency of an atom to attract electrons

D. The energy required to remove an electron

Answer: (D)

Explanation

Ionization energy is the energy needed to remove an electron from an atom. The tendency to attract electrons describes electronegativity rather than ionization energy.

23. What does electronegativity describe?

A. An atom’s energy requirement for losing electrons

B. An atom’s energy release during nuclear decay

C. An atom’s tendency to attract neutrons

D. An atom’s tendency to attract electrons

Answer: (D)

Explanation

Electronegativity describes how strongly an atom tends to attract electrons. The energy needed to remove an electron is ionization energy, which measures a different property.

24. Compared with lithium, how does fluorine’s stronger nuclear attraction affect its atomic properties?

A. Fluorine has a smaller radius, lower ionization energy, and weaker electron attraction

B. Fluorine has a smaller radius, higher ionization energy, and stronger electron attraction

C. Fluorine has a larger radius, lower ionization energy, and weaker electron attraction

D. Fluorine has a larger radius, higher ionization energy, and stronger electron attraction

Answer: (B)

Explanation

Greater nuclear attraction pulls electrons closer, producing a smaller atomic radius, greater ionization energy, and stronger electron attraction, as seen for fluorine compared with lithium. A larger radius would generally indicate weaker rather than stronger nuclear attraction.