RISE Science — Chemistry

An atom of carbon has an atomic number of 6 and a mass number of 14. Which statement accurately describes the subatomic composition of this carbon isotope (Carbon-14)?

• AIt contains 6 protons, 8 neutrons, and 6 electrons.
• BIt contains 6 protons, 6 neutrons, and 8 electrons.
• CIt contains 8 protons, 6 neutrons, and 6 electrons.
• DIt contains 14 protons, 6 neutrons, and 14 electrons.

Naturally occurring chlorine exists as two stable isotopes: Chlorine-35 (atomic mass 34.97 amu, abundance 75.77%) and Chlorine-37 (atomic mass 36.97 amu, abundance 24.23%). What is the calculated average atomic mass of chlorine?

• A35.45 amu
• B36.00 amu
• C35.97 amu
• D34.97 amu

What is the ground-state electron configuration of a neutral nitrogen atom (atomic number 7)?

• A1s² 2s² 2p³
• B1s² 2s² 2p⁵
• C1s² 2s³ 2p²
• D1s² 2p⁵

An element has the noble-gas electron configuration [Ne] 3s² 3p⁴. Which element does this configuration represent, and how many valence electrons does it have?

• ASulfur, with 6 valence electrons
• BSulfur, with 4 valence electrons
• CPhosphorus, with 5 valence electrons
• DOxygen, with 6 valence electrons

Which general trend best describes atomic radius as you move from left to right across Period 3 (Na to Cl) of the periodic table?

• AAtomic radius decreases because effective nuclear charge increases, pulling valence elect…
• BAtomic radius increases because additional electrons create stronger electron-electron re…
• CAtomic radius remains constant because electrons are added to the same principal energy l…
• DAtomic radius decreases because nuclear mass decreases across the period.

Why does first ionization energy generally decrease as you move down Group 1 (alkali metals) from Lithium to Cesium?

• AThe outermost electron is farther from the nucleus and shielded by more inner electron sh…
• BThe nuclear charge decreases down the group, reducing nuclear attraction for valence elec…
• CThe atomic radius decreases down the group, bringing valence electrons closer to the nucl…
• DThe number of valence electrons increases down the group, increasing mutual repulsion.

When a sodium vapor lamp is energized, it emits a distinct bright yellow light. What subatomic process is responsible for producing this emission spectrum?

• AElectrons drop from higher excited energy levels to lower ground states, releasing photon…
• BProtons absorb thermal energy and emit electromagnetic radiation as they move within the…
• CElectrons absorb energy and jump from lower energy levels to higher excited states.
• DElectrons are permanently ejected from the sodium atoms, generating free photons.

The speed of light is 3.00 × 10⁸ m/s and Planck's constant is 6.626 × 10⁻³⁴ J·s. What is the energy of a photon emitted from a red laser pointer with a wavelength of 6.63 × 10⁻⁷ m?

• A3.00 × 10⁻¹⁹ J
• B4.39 × 10⁻⁴⁰ J
• C1.32 × 10⁻²⁵ J
• D2.21 × 10⁻²⁷ J

Which isoelectronic species has the largest ionic radius: N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺, or Al³⁺?

• AN³⁻
• BAl³⁺
• CF⁻
• DNa⁺

What is the ground-state electron configuration of a neutral iron atom (Fe, atomic number 26)?

• A[Ar] 4s² 3d⁶
• B[Ar] 4s¹ 3d⁷
• C[Ar] 3d⁸
• D[Ar] 4s² 4p⁶

When an iron atom forms an Fe²⁺ ion, which electrons are removed first?

• AThe two 4s valence electrons
• BTwo electrons from the 3d subshell
• COne 4s electron and one 3d electron
• DTwo 3p core electrons

An element X has the following successive ionization energies: IE₁ = 578 kJ/mol, IE₂ = 1817 kJ/mol, IE₃ = 2745 kJ/mol, and IE₄ = 11,577 kJ/mol. In which group of the periodic table is element X located?

• AGroup 13 (3 valence electrons, e.g., Aluminum)
• BGroup 1 (1 valence electron, e.g., Sodium)
• CGroup 2 (2 valence electrons, e.g., Magnesium)
• DGroup 14 (4 valence electrons, e.g., Silicon)

Which of the following elements has the highest electronegativity according to the Pauling scale?

• AFluorine (F)
• BOxygen (O)
• CChlorine (Cl)
• DCesium (Cs)

Why is the ionic radius of a sodium cation (Na⁺) significantly smaller than the atomic radius of a neutral sodium atom (Na)?

• ANa⁺ loses its entire n=3 valence shell and has 11 protons attracting only 10 remaining el…
• BNa⁺ gains a proton in the nucleus, pulling the remaining electron cloud tighter.
• CNa⁺ loses electrons from its inner 1s core subshell.
• DNa⁺ experiences increased electron-electron repulsion among its valence electrons.

Which quantum number set (n, l, m_l, m_s) is permissible for a valence electron in a ground-state carbon atom?

• An = 2, l = 1, m_l = 0, m_s = +1/2
• Bn = 2, l = 2, m_l = 0, m_s = +1/2
• Cn = 1, l = 1, m_l = 0, m_s = -1/2
• Dn = 2, l = 1, m_l = +2, m_s = +1/2

Copper has an anomalous ground-state electron configuration. What is the correct electron configuration for a neutral copper atom (atomic number 29)?

• A[Ar] 4s¹ 3d¹⁰
• B[Ar] 4s² 3d⁹
• C[Ar] 4s⁰ 3d¹¹
• D[Ar] 4s² 4p⁹

How many unpaired electrons are present in a ground-state gaseous phosphorus atom (atomic number 15)?

• A3
• B1
• C0
• D5

Which statement correctly compares effective nuclear charge (Zeff) across Period 2 elements (Lithium to Fluorine)?

• AZeff increases from Li to F because nuclear charge (protons) increases while core electro…
• BZeff decreases from Li to F because added valence electrons shield each other perfectly.
• CZeff remains constant across Period 2 because all elements have 2 core electrons.
• DZeff increases from Li to F because the number of principal energy levels increases.

A mass spectrometer produces two main peaks for a sample of element X: Peak 1 at 10.01 amu (abundance 19.9%) and Peak 2 at 11.01 amu (abundance 80.1%). What is the identity of element X?

• ABoron (B, average atomic mass ~10.81 amu)
• BBeryllium (Be, average atomic mass ~9.01 amu)
• CCarbon (C, average atomic mass ~12.01 amu)
• DNeon (Ne, average atomic mass ~20.18 amu)

Which of the following elements has the smallest atomic radius?

• AHelium (He)
• BFrancium (Fr)
• CFluorine (F)
• DHydrogen (H)

Why is the second ionization energy (IE₂) of potassium (K) drastically higher than its first ionization energy (IE₁)?

• AIE₁ removes the single 4s valence electron, but IE₂ requires removing an electron from a…
• BIE₂ requires removing a proton from the nucleus.
• CIE₁ creates a dipositive ion, whereas IE₂ creates a monopositive ion.
• DPotassium's nuclear charge decreases after the first electron is removed.

Electrons fill orbitals according to specific rules. Which principle states that no two electrons in an atom can have the exact same set of four quantum numbers?

• APauli Exclusion Principle
• BAufbau Principle
• CHund's Rule
• DHeisenberg Uncertainty Principle

A sample of naturally occurring copper consists of ⁶³Cu (mass 62.93 amu) and ⁶⁵Cu (mass 64.93 amu). Given that copper's reported atomic mass is 63.55 amu, what is the approximate percent abundance of ⁶³Cu?

• A69%
• B31%
• C50%
• D85%

Which element has chemical properties most similar to Calcium (Ca)?

• AStrontium (Sr)
• BPotassium (K)
• CScandium (Sc)
• DBromine (Br)

Which electron transition in a hydrogen atom emits the photon with the shortest wavelength?

• An = 4 to n = 1
• Bn = 2 to n = 1
• Cn = 4 to n = 3
• Dn = 1 to n = 4

Which pair of atoms is most likely to form an ionic bond?

• ASodium (Na) and Fluorine (F)
• BCarbon (C) and Oxygen (O)
• CNitrogen (N) and Hydrogen (H)
• DChlorine (Cl) and chlorine (Cl)

What bonding model explains why solid metals like copper and aluminum conduct electricity and can be hammered into thin sheets (malleability)?

• APositive metal cations surrounded by a delocalized 'sea of mobile valence electrons'
• BRigid lattice of alternating positive and negative ions held by localized electrostatic f…
• CDirectional covalent bonds formed by shared electron pairs between adjacent atoms
• DWeak intermolecular dispersion forces holding discrete neutral metallic molecules

According to VSEPR theory, what is the molecular geometry (shape) and bond angle of a methane molecule (CH₄)?

• ATetrahedral, 109.5°
• BSquare planar, 90°
• CTrigonal planar, 120°
• DBent, 104.5°

Why is a water molecule (H₂O) bent in shape with a H-O-H bond angle of approximately 104.5°, rather than linear (180°)?

• AThe two unshared lone pairs on oxygen exert stronger repulsion than bonding pairs, pushin…
• BHydrogen atoms repel each other strongly, bending the molecule.
• CThe oxygen atom forms double bonds with both hydrogen atoms.
• DWater is nonpolar, requiring a bent shape to cancel dipole moments.

Both carbon dioxide (CO₂) and water (H₂O) contain polar covalent bonds. Why is CO₂ nonpolar overall, while H₂O is polar?

• ACO₂ is linear (180°), so its two equal dipole moments point in opposite directions and ca…
• BC-O bonds are nonpolar covalent, whereas O-H bonds are ionic.
• CCO₂ has lone pairs on its central atom, whereas H₂O has no lone pairs.
• DCarbon is more electronegative than Oxygen, making CO₂ neutral.

Which of the following compounds exhibits hydrogen bonding as its primary intermolecular force in the liquid state?

• AAmmonia (NH₃)
• BMethane (CH₄)
• CHydrogen chloride (HCl)
• DHydrogen sulfide (H₂S)

Boron trifluoride (BF₃) is an exception to the octet rule. What is the molecular geometry of BF₃ and how many valence electrons surround the central boron atom in its Lewis structure?

• ATrigonal planar, with 6 valence electrons (incomplete octet)
• BTrigonal pyramidal, with 8 valence electrons
• CTetrahedral, with 8 valence electrons
• DT-shaped, with 10 valence electrons (expanded octet)

Sulfur hexafluoride (SF₆) contains an expanded octet. What is the molecular geometry of SF₆ and the hybridization of the central sulfur atom?

• AOctahedral, with sp³d² hybridization
• BTrigonal bipyramidal, with sp³d hybridization
• CTetrahedral, with sp³ hybridization
• DSquare planar, with dsp² hybridization

What is the formal charge on the central nitrogen atom in a nitrate ion (NO₃⁻)?

• A+1
• B0
• C-1
• D+2

What key feature characterizes resonance structures for molecules such as Ozone (O₃) or Nitrate (NO₃⁻)?

• AThe actual molecule is a single hybrid structure with delocalized pi electrons and interm…
• BThe molecule rapidly oscillates back and forth between discrete Lewis structures.
• CThe positions of atomic nuclei shift continuously within the molecule.
• DThe molecule contains single and double bonds that alternate in length over time.

Why does normal Pentane (C₅H₁₂) have a higher boiling point (36.1 °C) than its structural isomer Neopentane (C(CH₃)₄, 9.5 °C)?

• APentane is a linear chain with a larger surface area, allowing stronger London dispersion…
• BPentane forms dipole-dipole interactions, whereas neopentane is nonpolar.
• CNeopentane contains strong intramolecular hydrogen bonds that lower its boiling point.
• DPentane has a higher molar mass than neopentane.

Which of the following compounds has the highest melting point?

• AMagnesium Oxide (MgO)
• BSodium Chloride (NaCl)
• CWater (H₂O)
• DMethane (CH₄)

Which molecule contains exactly one triple covalent bond?

• ANitrogen gas (N₂)
• BOxygen gas (O₂)
• CCarbon dioxide (CO₂)
• DWater (H₂O)

What is the molecular geometry of xenon tetrafluoride (XeF₄)?

• ASquare planar
• BTetrahedral
• CSee-saw
• DSquare pyramidal

What is the hybridization of the carbon atoms in ethyne (acetylene, C₂H₂)?

• Asp
• Bsp²
• Csp³
• Dsp³d

How many sigma (σ) and pi (π) bonds are present in a molecule of hydrogen cyanide (HCN)?

• A2 sigma bonds and 2 pi bonds
• B3 sigma bonds and 1 pi bond
• C1 sigma bond and 3 pi bonds
• D4 sigma bonds and 0 pi bonds

Which property of liquids decreases as intermolecular forces (IMFs) become stronger?

• AVapor pressure
• BBoiling point
• CViscosity
• DSurface tension

What type of solid is diamond (crystalline carbon)?

• ANetwork covalent solid
• BIonic solid
• CMolecular solid
• DMetallic solid

Which of the following bonds is the most polar?

• AH-F
• BH-O
• CH-N
• DH-C

According to Lewis structure principles, how many total valence electrons must be accounted for in a carbonate ion (CO₃²⁻)?

• A24
• B22
• C18
• D26

What is the molecular geometry of sulfur dioxide (SO₂)?

• ABent
• BLinear
• CTrigonal planar
• DTetrahedral

Which of the following molecules has a permanent net dipole moment (is polar overall)?

• ASulfur dioxide (SO₂)
• BCarbon tetrachloride (CCl₄)
• CBeryllium difluoride (BeF₂)
• DSulfur hexafluoride (SF₆)

What happens to bond length and bond strength as the number of shared electron pairs between two carbon atoms increases from a single bond to a double bond to a triple bond?

• ABond length decreases while bond strength increases.
• BBond length increases while bond strength increases.
• CBond length decreases while bond strength decreases.
• DBoth bond length and bond strength remain unchanged.