Nokea
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.
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Which of the following reactions is a decomposition reaction?
1. 2H2 + O2 → 2H2O
2. 2Na + Cl2 → 2NaCl
3. CaCO3 → CaO + CO2
4. PbCO3(s) → PbO(s) + CO2(g)
- A. 1
- B. 2 and 3
- C. 4
- D. All of them are decomposition reactions.
Correct Answer: C
Rationale: A decomposition reaction involves a single compound breaking down into simpler substances. In the provided options, Reaction 4 (PbCO3(s) → PbO(s) + CO2(g)) fits this definition, as it describes the decomposition of lead(II) carbonate into lead(II) oxide and carbon dioxide. Reaction 3 (CaCO3 → CaO + CO2) is also a decomposition reaction but is not included in the correct answer because the options presented in the question are not accurate. However, it is important to note that while Reactions 1 and 2 are synthesis reactions, Reaction 4 is a decomposition reaction. Therefore, the correct answer is option C, indicating that Reaction 4 is a decomposition reaction
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.
What can be predicted by using the periodic table?
- A. The properties of each element
- B. The charges of polyatomic ions
- C. The number of isotopes for each element
- D. The potential for discovering new elements
Correct Answer: A
Rationale: The periodic table organizes elements based on their properties, such as atomic number, electron configuration, and chemical behavior. By examining an element's position on the periodic table, one can predict its properties, including its physical and chemical characteristics, reactivity, and other behaviors. This predictive ability is one of the fundamental strengths of the periodic table in understanding and working with elements. Therefore, the correct answer is A, as the periodic table allows for the prediction of the properties of each element based on its location and characteristics within the table.
What distinguishes the 20 common amino acids from each other?
- A. Color
- B. Size
- C. R-group
- D. None of the above
Correct Answer: C
Rationale: The correct answer is C: R-group. The 20 common amino acids share a common backbone structure, but what differentiates them from each other is the side chain or R-group attached to this backbone. The R-group varies in composition and properties among the different amino acids, influencing their overall characteristics and functions. Options A and B are not the primary distinguishing factors among amino acids. Option D is incorrect as the R-group is the key feature that sets apart the 20 common amino acids, contributing to their individual identities and roles in biological processes.
An element has 6 protons, 6 electrons, and 6 neutrons. What is its atomic number?
- A. 6
- B. 12
- C. 18
- D. Not enough information
Correct Answer: A
Rationale: The atomic number of an element is determined by the number of protons in its nucleus. Since the element in question has 6 protons, its atomic number is also 6. The number of neutrons and electrons does not impact the atomic number, which is solely based on the number of protons. Therefore, the correct answer is A: 6.