how many neutrons are in an atom of carbon 12

HESI A2

HESI A2 Chemistry

1. How many neutrons are in an atom of carbon-12?

A. 2
B. 4
C. 6
D. 24

Correct answer: C

Rationale: An atom of carbon-12 has 6 neutrons. The atomic number of carbon is 6, representing the number of protons. The atomic mass of carbon-12 is 12. To find the number of neutrons, subtract the atomic number from the atomic mass: 12 - 6 = 6 neutrons. Choice A, 2, is incorrect as it does not reflect the correct calculation for neutrons in carbon-12. Choice B, 4, is incorrect as it does not match the correct number of neutrons in carbon-12. Choice D, 24, is incorrect as it is significantly higher than the actual number of neutrons in carbon-12.

2. Why does fluorine have a higher ionization energy than oxygen?

A. Fluorine has a smaller number of neutrons.
B. Fluorine has a larger number of neutrons.
C. Fluorine has a smaller nuclear charge.
D. Fluorine has a larger nuclear charge.

Correct answer: D

Rationale: Fluorine has a higher ionization energy than oxygen because fluorine has a larger nuclear charge. The greater number of protons in the nucleus of fluorine attracts its electrons more strongly, making it harder to remove an electron from a fluorine atom compared to an oxygen atom. Choice A is incorrect as the number of neutrons does not directly affect ionization energy. Choice B is also incorrect for the same reason. Choice C is incorrect because a smaller nuclear charge would result in lower ionization energy, not higher.

3. What charge do Group IA elements have?

A. +1
B. +2
C. +3
D. 0

Correct answer: A

Rationale: Group IA elements, also known as alkali metals, have a +1 charge. They readily lose one electron to achieve a stable electron configuration, forming ions with a single positive charge. This makes +1 the correct choice. Choices B, C, and D are incorrect because alkali metals in Group IA typically lose one electron, so they do not have a +2, +3, or 0 charge.

4. Which state of matter has a definite volume but takes the shape of its container?

A. Gas
B. Liquid
C. Solid
D. Plasma

Correct answer: B

Rationale: The state of matter that has a definite volume but takes the shape of its container is a 'Liquid.' Liquids have a fixed volume but can change their shape to fit the container they are in. This property distinguishes liquids from solids, which have both a definite shape and volume, and gases, which do not have a fixed volume or shape. Therefore, the correct answer is 'Liquid.' Choice A, 'Gas,' is incorrect because gases do not have a definite volume or shape. Choice C, 'Solid,' is incorrect as solids have a definite shape and volume. Choice D, 'Plasma,' is incorrect because plasma is a state of matter where atoms have been ionized and do not have a fixed volume or shape.

5. What is the mass number of an atom with 6 protons, 6 neutrons, and 6 electrons?

A. 12
B. 18
C. 6
D. 8

Correct answer: A

Rationale: The mass number of an atom is the sum of protons and neutrons. In this case, the atom has 6 protons and 6 neutrons, thus the mass number is 6 + 6 = 12. Therefore, choice A (12) is the correct answer. Choices B (18), C (6), and D (8) are incorrect because the mass number is determined by the sum of protons and neutrons, not the number of electrons or a different combination of particles.