What are isotopes? Definition and examples for high school physics

📚 Quick Study Guide

• ⚛️ Isotopes are variants of a chemical element which have the same number of protons and electrons, but a different number of neutrons. This means they have the same atomic number but different mass numbers.
• 🔢 The atomic number ($Z$) is the number of protons in the nucleus, which defines the element.
• ⚖️ The mass number ($A$) is the total number of protons and neutrons in the nucleus. So, $A = Z + N$, where $N$ is the number of neutrons.
• 🧪 Isotopes of an element have nearly identical chemical properties but may differ in physical properties like mass and stability.
• ☢️ Some isotopes are stable, while others are radioactive, meaning they decay over time. Radioactive isotopes have various applications in medicine, archaeology, and industry.
• 🗓️ Isotopic notation is often written as $^{A}_{Z}X$, where $X$ is the element symbol, $A$ is the mass number, and $Z$ is the atomic number. For example, Carbon-12 is written as $^{12}_{6}C$.
• ⚗️ Examples include Hydrogen-1 ($^{1}_{1}H$), Hydrogen-2 (Deuterium, $^{2}_{1}H$), and Hydrogen-3 (Tritium, $^{3}_{1}H$). All are hydrogen, but with different numbers of neutrons.

Practice Quiz

1. Which of the following statements BEST describes isotopes?
   1. A. Atoms with the same number of neutrons but different numbers of protons.
   2. B. Atoms with the same number of protons but different numbers of neutrons.
   3. C. Atoms with the same mass number but different atomic numbers.
   4. D. Atoms with the same number of electrons but different numbers of protons.
2. What is the atomic number ($Z$) of an element?
   1. A. The number of neutrons in the nucleus.
   2. B. The total number of protons and neutrons in the nucleus.
   3. C. The number of protons in the nucleus.
   4. D. The number of electrons orbiting the nucleus.
3. If an atom has 6 protons and 8 neutrons, what is its mass number ($A$)?
   1. A. 6
   2. B. 8
   3. C. 14
   4. D. 2
4. Which notation correctly represents Carbon-14?
   1. A. $^{6}_{14}C$
   2. B. $^{14}_{8}C$
   3. C. $^{14}_{6}C$
   4. D. $^{8}_{14}C$
5. Deuterium is an isotope of hydrogen. How many neutrons does a deuterium atom have?
   1. A. 0
   2. B. 1
   3. C. 2
   4. D. 3
6. What makes radioactive isotopes different from stable isotopes?
   1. A. Radioactive isotopes have more protons.
   2. B. Radioactive isotopes undergo decay over time.
   3. C. Radioactive isotopes have fewer neutrons.
   4. D. Radioactive isotopes have a higher atomic number.
7. Which of the following is NOT a common application of radioactive isotopes?
   1. A. Medical treatments
   2. B. Archaeological dating
   3. C. Industrial gauging
   4. D. Producing table salt