group viia elements have what charge

HESI A2

Chemistry HESI A2 Quizlet

1. What charge do Group VIIA elements have?

A. -1
B. -2
C. 0
D. 1

Correct answer: A

Rationale: Group VIIA elements, also known as halogens, have a tendency to gain one electron to achieve a stable electron configuration, resulting in a -1 charge. This is because they have seven valence electrons and need one more to complete their octet, making them highly reactive in forming -1 ions. Therefore, the correct answer is A. Choice B (-2) is incorrect because Group VIIA elements typically gain one electron, not two. Choice C (0) is incorrect as these elements tend to form -1 ions by gaining one electron. Choice D (1) is incorrect because Group VIIA elements gain electrons to form negative ions, not positive ones.

2. How many neutrons are in an atom of uranium-235?

A. 92
B. 125
C. 143
D. 235

Correct answer: A

Rationale: The correct answer is A: '92'. To determine the number of neutrons in an atom, you subtract the atomic number (number of protons) from the atomic mass number. For uranium-235, the atomic number is 92, and the atomic mass number is 235. Subtracting 92 from 235 gives us 143 neutrons in an atom of uranium-235. Therefore, options B, C, and D are incorrect as they do not represent the correct number of neutrons in an atom of uranium-235.

3. Which one does not name a polar molecule?

A. NH₃
B. H₂S
C. SO₂
D. CO₂

Correct answer: A

Rationale: The correct answer is NH₃. The molecule NH₃ does not represent a polar molecule because nitrogen and hydrogen in this molecule have a small difference in electronegativity that does not result in a significant polar covalent bond. In contrast, molecules H₂S, SO₂, and CO₂ have polar covalent bonds due to larger electronegativity differences, making them polar molecules. Therefore, options B, C, and D are polar molecules, unlike option A.

4. What is the main component of air?

A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Argon

Correct answer: B

Rationale: Nitrogen is the main component of air, constituting approximately 78% of the Earth's atmosphere. Oxygen, carbon dioxide, and argon are also present in smaller amounts, but nitrogen is the most abundant gas in the air. Therefore, the correct answer is B. Choice A, oxygen, is essential for respiration but makes up only about 21% of the atmosphere. Choice C, carbon dioxide, is vital for photosynthesis but exists in trace amounts in the air. Choice D, argon, is a noble gas found in relatively small quantities in the atmosphere.

5. What is the role of a catalyst in a chemical reaction?

A. Slows down the reaction
B. Has no effect
C. Speeds up the reaction
D. Stops the reaction

Correct answer: C

Rationale: A catalyst speeds up a chemical reaction by lowering the activation energy required for the reaction to occur. It does not get consumed in the reaction and remains unchanged at the end, allowing it to facilitate multiple reaction cycles. Choice A is incorrect because a catalyst actually speeds up the reaction. Choice B is incorrect because catalysts do have an effect by accelerating the reaction. Choice D is incorrect because catalysts do not stop the reaction, but rather increase the reaction rate.