AP Chemistry Questions on Atomic Number, Mass Number, and Isotopes

🧪 Quick Study Guide

• ⚛️ The atomic number (Z) represents the number of protons in the nucleus of an atom. It defines the element.
• ⚖️ The mass number (A) represents the total number of protons and neutrons in the nucleus of an atom.
• ⚗️ Isotopes are atoms of the same element (same atomic number) that have different numbers of neutrons, resulting in different mass numbers.
• ➕ To calculate the number of neutrons, subtract the atomic number (Z) from the mass number (A): Number of neutrons = A - Z
• 📊 Isotopic abundance is the percentage of each isotope of an element that occurs naturally.
• 💲 The average atomic mass is calculated as the weighted average of the masses of the isotopes of an element: Average Atomic Mass = $\sum$ (Isotopic Mass $\times$ Fractional Abundance)

Practice Quiz

1. What does the atomic number of an element represent?
   1. The number of neutrons in the nucleus.
   2. The number of protons in the nucleus.
   3. The number of electrons in the outermost shell.
   4. The total number of particles in the nucleus.
2. An atom has a mass number of 39 and contains 19 protons. How many neutrons does it have?
   1. 19
   2. 20
   3. 39
   4. 58
3. Which of the following statements best describes isotopes?
   1. Atoms with the same number of neutrons but different numbers of protons.
   2. Atoms with the same number of protons but different numbers of neutrons.
   3. Atoms with the same mass number but different atomic numbers.
   4. Atoms with the same number of electrons but different numbers of protons.
4. Chlorine has two isotopes: Chlorine-35 and Chlorine-37. Chlorine-35 has an abundance of 75%, and Chlorine-37 has an abundance of 25%. What is the average atomic mass of chlorine?
   1. 35.0
   2. 35.5
   3. 36.0
   4. 37.0
5. An ion with a +2 charge contains 12 protons and 10 electrons. What is the atomic number of this ion?
   1. 10
   2. 12
   3. 22
   4. 24
6. What is the mass number of an oxygen atom that has 8 protons, 8 electrons, and 9 neutrons?
   1. 8
   2. 16
   3. 17
   4. 25
7. Which of the following is NOT true regarding isotopes of the same element?
   1. They have the same chemical properties.
   2. They have the same number of protons.
   3. They have different numbers of neutrons.
   4. They have the same mass number.