The number of protons in an atom determines its atomic number and its identity as a specific element.
Correct Answer
True
The atomic number (Z) is defined by the number of protons, which uniquely identifies an element.
Question 2
Isotopes of an element have the same number of neutrons but different numbers of protons.
Correct Answer
False
Isotopes of an element have the same number of protons but different numbers of neutrons. The number of protons defines the element.
Question 3
As one moves down a group in the periodic table, the atomic radius generally increases due to the addition of electron shells.
Correct Answer
True
Moving down a group adds principal energy levels, increasing the average distance of the outermost electrons from the nucleus, thus increasing atomic radius.
Question 4
The first ionization energy generally increases across a period from left to right because the effective nuclear charge decreases.
Correct Answer
False
The first ionization energy generally increases across a period from left to right because the effective nuclear charge *increases*, pulling valence electrons more strongly and making them harder to remove.
Question 5
Electronegativity is the energy change that occurs when an electron is added to a gaseous atom.
Correct Answer
False
Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. The energy change when an electron is added to a gaseous atom is electron affinity.
Question 6
A molecule with polar bonds can be nonpolar overall if its molecular geometry results in the symmetrical cancellation of bond dipoles.
Correct Answer
True
For example, carbon tetrachloride (CCl4) has polar C-Cl bonds, but its tetrahedral geometry causes the individual bond dipoles to cancel, making the molecule nonpolar.
Question 7
The VSEPR theory predicts that the electron geometry around a central atom with four electron domains and two lone pairs will be tetrahedral.
Correct Answer
True
Four electron domains (whether bonding or lone pairs) around a central atom always result in a tetrahedral electron geometry. The molecular geometry in this specific case would be bent.
Question 8
Pi (π) bonds are formed by the direct, head-on overlap of atomic orbitals along the internuclear axis.
Correct Answer
False
Pi (π) bonds are formed by the *sideways* overlap of p orbitals above and below the internuclear axis. Sigma (σ) bonds are formed by head-on overlap along the internuclear axis.
Question 9
Hybridization of atomic orbitals is used to explain the observed molecular geometries that cannot be described by simple atomic orbital overlap.
Correct Answer
True
Hybridization allows for the formation of equivalent bonds and explains bond angles observed in molecules like methane (sp3 hybridization), which would not be predicted by unhybridized orbitals.
Question 10
In a chemical reaction, the limiting reactant is completely consumed and determines the maximum amount of product that can be formed.
Correct Answer
True
The limiting reactant dictates the theoretical yield of a reaction because it is the reactant that runs out first, stopping the reaction.
Question 11
The percent yield of a reaction is calculated by dividing the theoretical yield by the actual yield and multiplying by 100%.
Correct Answer
False
The percent yield is calculated by dividing the *actual yield* by the *theoretical yield* and multiplying by 100%.
Question 12
For an endothermic reaction, the enthalpy change (ΔH) is positive, indicating that the system absorbs heat from the surroundings.
Correct Answer
True
Endothermic processes are characterized by the absorption of energy from the surroundings, resulting in a positive ΔH value.
Question 13
A reaction with a negative ΔG is always spontaneous at all temperatures.
Correct Answer
False
A reaction with a negative ΔG is spontaneous, but spontaneity can be temperature-dependent if both ΔH and ΔS have the same sign. For example, if ΔH is positive and ΔS is positive, ΔG becomes negative only at high temperatures.
Question 14
The standard enthalpy of formation (ΔHf°) for any pure element in its standard state is zero.
Correct Answer
True
By definition, the enthalpy of formation for an element in its most stable form under standard conditions (e.g., O2(g), C(graphite)) is zero.
Question 15
At equilibrium, the concentrations of reactants and products are equal.
Correct Answer
False
At equilibrium, the *rates of the forward and reverse reactions are equal*, leading to constant (but not necessarily equal) concentrations of reactants and products.
Question 16
If Q < K for a reversible reaction, the reaction will proceed in the reverse direction to reach equilibrium.
Correct Answer
False
If Q < K, the ratio of products to reactants is too small relative to equilibrium, so the reaction will proceed in the *forward direction* (towards products) to reach equilibrium.
Question 17
Adding a catalyst to a system at equilibrium will shift the equilibrium position towards the products.
Correct Answer
False
A catalyst increases the rates of both the forward and reverse reactions equally, allowing the system to reach equilibrium faster, but it does not shift the position of the equilibrium.
Question 18
A strong acid completely dissociates in water, producing a high concentration of H3O+ ions.
Correct Answer
True
Strong acids are defined by their complete ionization in aqueous solution, meaning they donate all their protons to water to form hydronium ions.
Question 19
The conjugate base of a weak acid is a strong base.
Correct Answer
False
The conjugate base of a weak acid is a *weak base*. Only the conjugate base of a very weak acid would be considered a strong base.
Question 20
A solution with a pH of 3 is 100 times more acidic than a solution with a pH of 5.
Correct Answer
True
The pH scale is logarithmic. A difference of 2 pH units (5-3=2) means a 10^2 = 100-fold difference in H+ concentration. A lower pH indicates higher acidity.
Question 21
According to the Brønsted-Lowry definition, an acid is a proton acceptor.
Correct Answer
False
According to the Brønsted-Lowry definition, an acid is a *proton donor*. A base is a proton acceptor.
Question 22
In an aqueous solution, the product of the hydrogen ion concentration and the hydroxide ion concentration (Kw) is constant at a given temperature.
Correct Answer
True
The ion product of water, Kw = [H+][OH-], is a temperature-dependent constant, typically 1.0 x 10^-14 at 25 °C.