Nokea
Which of the following elements is an alkali metal?
- A. magnesium
- B. rubidium
- C. hydrogen
- D. chlorine
Correct Answer: B
Rationale: Rubidium is the correct answer because alkali metals are found in Group 1 of the periodic table. Rubidium is located in Group 1 and exhibits properties typical of alkali metals, such as low melting points, high reactivity, and the tendency to form ionic compounds. Magnesium is an alkaline earth metal, hydrogen is a nonmetal, and chlorine is a halogen, so they do not belong to the alkali metal group.
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What occurs to an atom with a negative charge?
- A. Gained an electron
- B. Lost an electron
- C. Gained a proton
- D. Lost a proton
Correct Answer: A
Rationale: When an atom has a negative charge, it means it has gained an electron. Electrons are negatively charged particles, so when an atom gains an electron, it becomes negatively charged. This process is known as gaining an electron to achieve stability through a full outer electron shell. Atoms gain or lose electrons to attain a stable electron configuration, typically following the octet rule. In this case, gaining an electron is the correct choice as it results in the atom having a negative charge.
What is pH?
- A. The measure of concentration of H₃O⺠ions
- B. The measure of concentration of hydrogen ions
- C. The measure of concentration of Hâ‚‚O molecules
- D. None of the above
Correct Answer: A
Rationale: The correct answer is 'A: The measure of concentration of H₃O⺠ions.' pH is a measure of the concentration of hydronium ions (H₃Oâº) in a solution, indicating the acidity or alkalinity on a scale from 0 to 14. Values below 7 are acidic, 7 is neutral, and above 7 is alkaline/basic. Choice B is incorrect as pH specifically measures hydronium ions, not hydrogen atoms. Choice C refers to water (Hâ‚‚O), which is not directly related to pH measurement.
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.
Which of the following describes atomic mass?
- A. Mass of protons and electrons
- B. Mass of neutrons and electrons
- C. Average mass of that element's isotopes
- D. Number of moles in a solution
Correct Answer: C
Rationale: The correct answer is C: Average mass of that element's isotopes. Atomic mass is the weighted average mass of the isotopes of an element, considering the natural abundance of each isotope. It is not just the sum of protons and neutrons or neutrons and electrons. Understanding atomic mass is crucial in chemistry as it helps in determining the molar mass of elements, which is essential in various chemical calculations such as stoichiometry and reaction equations.
What is the atomic number?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number is the number of protons in an atom's nucleus. It uniquely identifies an element and determines its chemical properties. The number of neutrons and electrons can vary in an atom, but the number of protons remains constant for a specific element. Therefore, the correct answer is the 'Number of protons' (Choice B).