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Difficulty: EasyAtomic Structure and Periodic Table

An isotope of potassium has an atomic number of 1919 and a mass number of 3939. How many neutrons are present in the nucleus of this atom?

Answer: 20

Answer

The nucleus of this potassium atom contains 2020 neutrons.
The mass number (3939) represents the combined count of protons and neutrons in the nucleus. Because the atomic number is 1919, the atom has 1919 protons. Subtracting the protons from the mass number yields 39−19=2039 - 19 = 20 neutrons.

Step-by-Step Solution

1
Identify the atomic number and mass number from the problem statement.
Atomic number Z=19Z = 19, Mass number A=39A = 39.
The atomic number indicates the number of protons (1919), and the mass number indicates the total number of nucleons (3939).
2
Subtract the atomic number from the mass number to calculate the number of neutrons.
N=39−19=20N = 39 - 19 = 20
The number of neutrons is determined by subtracting the number of protons from the mass number (N=A−ZN = A - Z).

Key Concept

Calculating subatomic particle counts in an isotope using the relationship between mass number, atomic number, and neutrons (N=A−ZN = A - Z).
Estimated Time:40s
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Topics

Atomic Structure and Periodic Table

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