MCAT General Chemistry Discrete Question Set 24: Atomic & Nuclear Structure

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Deborah Lindsey
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1 MCAT General Chemistry Discrete Question Set 24: Atomic & Nuclear Structure Question No. 1 of How many protons and neutrons would be found in an atom of Iron with an atomic mass of 56 and an atomic number of 26? Question #01 (A) 56 protons and 26 neutrons (B) 56 neutrons and 26 protons (C) 26 protons and 30 neutrons (D) 30 protons and 26 neutrons A: Incorrect. Atomic mass is equal to protons + neutrons and atomic number is equal to number of protons. B: Incorrect. Atomic mass is equal to protons + neutrons and atomic number is equal to number of protons. C: Correct. Atomic mass is equal to protons + neutrons and atomic number is equal to number of protons. D: Incorrect. Atomic mass is equal to protons + neutrons and atomic number is equal to number of protons. Define atomic number and atomic mass : Atomic number is the number, equal to the number of protons in an atom that determines its chemical properties. Symbol: Z Atomic mass is the mass of an atom expressed in atomic mass units. Always associate the atomic number with the number of protons and the atomic mass with the sum of the number of protons and neutrons. 26 protons would require an atomic number of 26 and 30 neutrons means that the atomic mass would be or 56. This DOES meet the situation described in the question, where the atomic number was 26 and the atomic mass is 56. Answer: (C) 26 protons and 30 neutrons

2 Question No. 2 of 10 We have found the mass defect for an atom to be 0.04 amu. What is the binding energy for that atom in Joules? Question #02 (A) 5.93 x (B) 4.67 x (C) 1.99 x (D) 6.64 x A: Correct. Mass defect is the difference between the mass of an atom and the sum of the masses of its individual components. B: Incorrect. Mass defect is the difference between the mass of an atom and the sum of the masses of its individual components. C: Incorrect. Mass defect is the difference between the mass of an atom and the sum of the masses of its individual components. D: Incorrect. Mass defect is the difference between the mass of an atom and the sum of the masses of its individual components. Define mass defect and binding energy : Mass defect is defined as The difference between the mass of an atom and the sum of the masses of its individual components. Binding energy is defined as The energy needed to separate the constituent parts of an atom or nucleus. When doing any calculation, check all of your work for consistent dimensions. In this case, the conversion to kg must take place initially to give us a result that has units of joules. The correct answer is a result of properly converting amu to kg, and then using E=mc 2 where we know m and c and calculate E. Answer: (A)

3 Question No. 3 of 10 3: An atom undergoes radioactive decay, but both the atomic number and the atomic mass remain the same. Which of the following was probably the type of radiation that was given off? Question #03 (A) Alpha radiation (B) Beta radiation (C) Gamma radiation (D) It is not possible to determine. A: Incorrect. Alpha radiation is 2 protons and 2 neutrons. This would change the atomic mass and atomic number of an atom. B: Incorrect. Beta radiation is the release of an electron when a neutron converts to a proton. This would change the atomic number of an atom. C: Correct. Gamma radiation is the release of a high energy packet that would not change the atomic mass or atomic number. D: Incorrect. There is a correct answer listed. Characterize Gamma decay : Gamma decay occurs when a high energy packet of energy (or photon) is expelled from a nucleus. There is a tendency to think of radiation as something tangible it has mass and we can discuss the particles involved. Gamma radiation, however, deals with energy being expelled, so that the result is a less energetic, more stable nucleus. Beta radiation results in a neutron converting into a proton as it emits an electron (beta particle). This changes the nucleus of the original into that of another element with an atomic number one greater than the original. Answer: (C) Gamma Radiation

4 Question No. 4 of 10 4: A friend hypothesizes that after three half lives, about 33% of the original atoms have not decayed. Which of the following best describes a correct reaction on your part? Question #04 (A) You are very intelligent I am glad that you understand this concept so well. (B) I am sorry but you are quite incorrect, it will all be decayed. (C) I am sorry but you are quite incorrect because about 13% of the original atoms will not have decayed. (D) I am sorry but you are quite incorrect because about 25% of the original atoms will not have decayed. A: Incorrect. After 1 half life = 50%. After the second half-life = 25%. After the third half life = about 13% B: Incorrect. After 1 half life = 50%. After the second half-life = 25%. After the third half life = about 13% C: Correct. After 1 half life = 50%. After the second half-life = 25%. After the third half life = about 13% D: Incorrect. After 1 half life = 50%. After the second half-life = 25%. After the third half life = about 13% Define Half life Half life if the time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay. So after one half life, 50% of the original is left. After two half lives, half of the 50% or 25% will be left. When working with half life, counting on fingers can sometimes be as valuable as having a calculator. You can use your fingers to keep track of how many times half lives have passed, and mentally or verbally keep cutting the number you are starting with in half. After two half lives, 25% of the original atoms would remain. A third half life would bring the decay of half of that 25% and leave 12.5% of the original amount. Since this is approximately 13%, this signals a correct answer. Answer: (C)

5 Question No. 5 of 10 5: Which of the following is the joining of two smaller nuclei to form a larger one? Question #05 (A) Nuclear fission (B) Nuclear fusion (C) Alpha radiation (D) Beta radiation A: Incorrect. Fission is the splitting of a larger atom. B: Correct. Fusion is the joining of two smaller nuclei. C: Incorrect. Alpha radiation is the release of a helium nucleus from the nucleus. D: Incorrect. Beta radiation is the release of an electron when a neutron converts to a proton. When you re joining 2 nuclei, you re fusing them together. It s Nuclear Fusion Answer: (B) Nuclear Fusion

6 Question No. 6 of 10 Question #06 6: Complete the following equation: Ra Rn? (A) α β (B) (C) 1 0 n (D) 1 e 4 2 A: Correct. The change of 4 in mass number and the change of 2 in atomic number indicate the release of an alpha particle. B: Incorrect. The change of 4 in mass number and the change of 2 in atomic number indicate the release of an alpha particle. C: Incorrect. The change of 4 in mass number and the change of 2 in atomic number indicate the release of an alpha particle. D: Incorrect. The change of 4 in mass number and the change of 2 in atomic number indicate the release of an alpha particle. Superscripts: 226 = 222 +?? = 4 Subscripts: 88 = 86 +?? = 2 This is an alpha particle Answer: (A) 4 2 α

7 Question No. 7 of 10 7: Complete the following equation:? + β Li Question #07 (A) (B) (C) (D) 7 He Be Li N A: Incorrect. The atomic numbers do not balance. B: Correct. The atomic number and atomic mass balance. C: Incorrect. Lithium does not have an atomic number of 4. D: Incorrect. Nitrogen does not have an atomic number of 4. Superscript:? + 0 = 7? = 7 Subscripts:? + (-1) = 3? = 4 Atom with an atomic number of 4 is beryllium Answer: (B) Be 7 4

8 Question No. 8 of 10 Question #08 8: Complete the following equation: Se Se? (A) α β (B) (C) 1 0 n (D) 1 e 4 2 A: Incorrect. The atomic mass and atomic number are not balanced. B: Incorrect. The atomic mass and atomic number are not balanced. C: Correct. The atomic mass and atomic number are balanced. D: Incorrect. The atomic mass and atomic number are not balanced. Superscript: 91 = 90 +?? = 1 Subscripts: 34 = 34 +?? =0 This is a neutron Answer: (C) n 1 0

9 Question No. 9 of 10 9: Complete the following equation: Na ? 1 β Question #09 (A) (B) (C) (D) Cr Ne Mg Na A: Incorrect. The atomic mass and atomic number are not balanced. B: Incorrect. The atomic mass and atomic number are not balanced. C: Correct. The atomic mass and atomic number are balanced. D: Incorrect. The atomic mass and atomic number are not balanced. Superscript: 24 =? + 0? = 24 Subscripts: 11 =? + (-1)? =12 An atom with an atomic number of 12 is magnesium Answer: (C) Mg 24 12

10 Question No. 10 of 10 10: Complete the following equation: Ti + β ? Question #10 (A) (B) (C) (D) Ru V Ti Sc A: Incorrect. Ru is not atom number 21. B: Incorrect. The atomic mass and atomic number are not balanced. C: Incorrect. This is not atom number 21. D: Correct. The atomic mass and atomic number are balanced & Sc is atom number 21. Superscript: =?? = 44 Subscripts: 22 + (-1) =?? =21 An atom with an atomic number of 21 is Sc Answer: (D) Sc 44 21

Feedback D. Incorrect. Atomic mass is equal to protons + neutrons and atomic number is equal to number of protons.

Feedback D. Incorrect. Atomic mass is equal to protons + neutrons and atomic number is equal to number of protons. CLEP Chemistry - Problem Drill 22: Nuclear Reactions No. 1 of 10 1. How many protons and neutrons would be found in an atom of Iron with an atomic mass of 56 and an atomic number of 26? (A) 56 protons