An ion has 19 protons, 20 neutrons, and 18 electrons. What is the correct isotope notation?
A. ${}_{19}^{39} K^{-1}$
B. ${}_{19}^{39} K^{+1}$
C. ${}_{18}^{19} K^{+1}$
Answer (1)
Determine the atomic number (Z) from the number of protons: Z = 19 , which identifies the element as potassium (K).
Calculate the mass number (A) by summing protons and neutrons: A = 19 + 20 = 39 .
Find the charge by subtracting the number of electrons from the number of protons: c ha r g e = 19 − 18 = + 1 .
Write the isotope notation as Z A X c ha r g e : 19 39 K + 1 .
The correct isotope notation is 19 39 K + 1 .
Explanation
Understanding Isotope Notation Let's break down how to determine the correct isotope notation for an ion. We'll start by identifying the key components and then assemble them into the correct format.
Determining Atomic Number The atomic number (Z) is the number of protons in the nucleus of an atom. This determines the element. In this case, the ion has 19 protons, so the atomic number is 19. The element with atomic number 19 is potassium (K).
Calculating Mass Number The mass number (A) is the total number of protons and neutrons in the nucleus. Here, we have 19 protons and 20 neutrons, so the mass number is 19 + 20 = 39 .
Determining the Charge The charge of an ion is determined by the difference between the number of protons (positive charges) and the number of electrons (negative charges). In this case, we have 19 protons and 18 electrons, so the charge is 19 − 18 = + 1 .
Writing the Isotope Notation Now, we combine all this information to write the isotope notation. The general form is Z A X c ha r g e , where:
Z is the atomic number,
A is the mass number,
X is the element symbol, and
charge is the ion's charge.
So, for our ion, the isotope notation is 19 39 K + 1 .
Final Answer Therefore, the correct isotope notation for the ion with 19 protons, 20 neutrons, and 18 electrons is 19 39 K + 1 .
Examples
Isotope notation is used in various fields, such as nuclear chemistry, geology, and medicine. For example, in carbon dating, scientists use the isotope 14 C to determine the age of organic materials. In medicine, radioactive isotopes like 131 I are used in diagnostic imaging and cancer treatment. Understanding isotope notation is crucial for accurately representing and interpreting data in these applications.
