HESI A2 Chemistry

Correct Answer: C

Rationale: The correct answer is C: 6. In an atom of carbon-12, the atomic number (number of protons) is 6. Since the atomic number represents the number of protons, to find the number of neutrons, we subtract the atomic number from the mass number. Carbon-12 has a mass number of 12, so 12 - 6 = 6 neutrons. Other choices are incorrect because: A: 2 - This is not correct because the number of neutrons is not equal to the atomic number in carbon-12. B: 4 - This is incorrect as it does not consider the correct calculation based on the atomic number and mass number. D: 24 - This answer is incorrect as it is not related to the atomic structure of carbon-12.

Correct Answer: B

Rationale: The correct formula for potassium chloride is KCl. "K" represents potassium and "Cl" represents chloride. Potassium is a metal with a +1 charge, while chloride is a non-metal with a -1 charge. When these two ions combine, they form a neutral compound with a 1:1 ratio, resulting in the formula KCl. Choice A (NaCl) is incorrect because "Na" represents sodium, not potassium. Choice C (KCl) is also incorrect because it is the same as the correct answer. Choice D (ClK) is incorrect as the order of elements in a chemical formula matters, and in this case, it should be KCl to represent potassium chloride accurately.

Correct Answer: D

Rationale: The correct answer is D: ionization energy. Ionization energy is the energy needed to remove an electron from an atom. The outermost electron requires the least amount of energy to remove as it is farthest from the nucleus. This process results in the formation of a positively charged ion. Explanation: 1. Covalent bonding (A) refers to the sharing of electrons between atoms, not the energy required to remove an electron. 2. Electronegativity (B) is the ability of an atom to attract electrons in a chemical bond, not the energy needed to remove an electron. 3. Atomic radius (C) is the size of an atom, which does not directly relate to the energy required to remove an electron.

Correct Answer: B

Rationale: The correct answer is B: Sum of protons and neutrons. Atomic mass is the total mass of an atom, which is the combined mass of protons and neutrons in the nucleus. This value is measured in atomic mass units (amu). Choice A is incorrect because it refers to the atomic number (number of protons). Choice C is incorrect as it only considers the number of neutrons, not the total mass. Choice D is incorrect because atomic mass is not an average weight but a specific value for a single atom.

Correct Answer: D

Rationale: The correct answer is D: W (tungsten). Tungsten has the greatest atomic mass among the elements listed. Tungsten has an atomic number of 74, which corresponds to an atomic mass of approximately 183.84 g/mol. Gold (Au) has an atomic number of 79, with an atomic mass of around 196.97 g/mol, making it heavier than barium (Ba) and iodine (I). Barium has an atomic number of 56, with an atomic mass of about 137.33 g/mol, and iodine has an atomic number of 53, with an atomic mass of roughly 126.90 g/mol. Therefore, tungsten (W) has the greatest atomic mass compared to the other elements listed.