One isotope of sodium has 11 protons and 7 neutrons. What is the mass number of this isotope?
A. 4
B. 7
C. 11
D. 18
Answer (2)
The mass number of the sodium isotope with 11 protons and 7 neutrons is 18. This is calculated by adding the number of protons and neutrons together. Therefore, the correct answer is D. 18.
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The mass number is the sum of protons and neutrons.
Add the number of protons (11) and neutrons (7): 11 + 7 = 18 .
The mass number of the isotope is 18 .
Explanation
Understanding the Problem We are given an isotope of sodium that has 11 protons and 7 neutrons. The problem asks us to find the mass number of this isotope.
Finding the Mass Number The mass number of an isotope is the total number of protons and neutrons in the nucleus of an atom. To find the mass number, we simply add the number of protons and the number of neutrons.
Calculation In this case, the number of protons is 11 and the number of neutrons is 7. Therefore, the mass number is: M a ss u mb er = N u mb er u mb ero f u mb er P ro t o n s + N u mb er u mb ero f u mb er N e u t ro n s M a ss u mb er = 11 + 7 M a ss u mb er = 18
Final Answer The mass number of the isotope is 18.
Examples
In nuclear chemistry, determining the mass number of an isotope is crucial for understanding its stability and radioactive properties. For example, carbon-14, with 6 protons and 8 neutrons (mass number 14), is used in radiocarbon dating to determine the age of organic materials. Similarly, isotopes of uranium with different mass numbers exhibit varying levels of radioactivity, influencing their use in nuclear power and weapons. Understanding mass numbers helps scientists predict how an isotope will behave and what applications it might have.
