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What is the term for the number of protons in an atom?
- A. atomic identity
- B. atomic mass
- C. atomic weight
- D. atomic number
Correct Answer: D
Rationale: The term for the number of protons in an atom is the atomic number. The atomic number is a fundamental property of an element, representing the number of protons in an atom's nucleus. It serves as the unique identity of an element and determines its position on the periodic table and its chemical behavior. Atomic mass refers to the average mass of an atom, including protons, neutrons, and electrons, while atomic weight is the average weight of an element considering the abundance of its isotopes. 'Atomic identity' is not a standard term in chemistry to describe the number of protons in an atom, making option D, 'atomic number,' the correct answer.
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Which type of bond involves sharing pairs of electrons?
- A. Ionic
- B. Covalent
- C. Both
- D. None of the above
Correct Answer: B
Rationale: In a covalent bond, atoms share pairs of electrons to achieve a stable electron configuration. This sharing of electrons leads to the formation of a strong bond between atoms. Ionic bonds, on the other hand, involve the transfer of electrons from one atom to another. Therefore, the correct answer is option B, Covalent, as it specifically describes the sharing of electron pairs, distinguishing it from ionic bonds where electron transfer occurs rather than electron sharing.
What defines the atomic number of an element?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number of an element is defined by the number of protons in the nucleus of its atom. This number uniquely identifies an element and determines its chemical properties. Neutrons and electrons are also present in the atom and are essential, but the atomic number specifically refers to the number of protons. The number of neutrons is not the atomic number but contributes to the isotope of an element. The number of electrons can vary, but the number of protons remains constant for a specific element.
What are van der Waals forces?
- A. the weak forces of attraction between two molecules
- B. the strong forces of attraction between two molecules
- C. hydrogen bonds
- D. conjugal bonds
Correct Answer: A
Rationale: Van der Waals forces are weak intermolecular forces that occur between non-polar molecules. These forces result from temporary fluctuations in electron distribution within the molecules, leading to slight positive and negative charges. This results in weak attraction between molecules through van der Waals forces. Hydrogen bonds, in contrast, are stronger intermolecular forces that specifically occur between molecules containing hydrogen bonded to a highly electronegative atom like oxygen or nitrogen. Conjugal bonds do not exist in chemistry and are not relevant to intermolecular forces.
How many hydrogen atoms are present in the reactants?
- A. 2
- B. 4
- C. 1
- D. None of the above
Correct Answer: B
Rationale: To determine the number of hydrogen atoms in the reactants, we need to examine the chemical formula of the reactants. If the formula contains hydrogen atoms, we count them to find the total. In this case, the correct answer is 4 because there are 4 hydrogen atoms present in the reactants. The chemical formula in the reactants indicates the presence of 4 hydrogen atoms. It is crucial to pay close attention to the elements and their quantities in chemical reactions to ensure accurate analysis and understanding of reactants and products.
Which type of reaction is most likely represented by the products CO2 + H2O: CO2 + H2O?
- A. Synthesis
- B. Decomposition
- C. Single replacement
- D. Combustion
Correct Answer: D
Rationale: The reaction products CO2 and H2O suggest a combustion reaction. In a combustion reaction, a substance reacts with oxygen gas (O2) to produce carbon dioxide (CO2) and water (H2O) as products. The given reaction matches the characteristic products of a combustion reaction, indicating that option D, 'Combustion,' is the correct answer.