A Potassium isotope contains 19 protons, 19 electrons and 21 neutrons. What is its mass number? 40
The Correct Answer and Explanation is :
The mass number of an isotope is the total number of protons and neutrons in its nucleus. In the case of the potassium isotope you mentioned, it contains 19 protons, 19 electrons, and 21 neutrons.
To calculate the mass number, you add the number of protons to the number of neutrons:
[
\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}
]
Substituting in the given values:
[
\text{Mass Number} = 19 \, (\text{protons}) + 21 \, (\text{neutrons}) = 40
]
Thus, the mass number of this potassium isotope is 40.
Explanation
In atomic structure, protons and neutrons are found in the nucleus of an atom, while electrons orbit around the nucleus. Protons have a positive charge, and the number of protons in an atom defines its atomic number, which determines the element. For potassium (K), the atomic number is 19, meaning it has 19 protons.
Neutrons, on the other hand, have no charge and contribute to the mass of the atom but do not affect its chemical behavior. The total number of protons and neutrons together gives the mass number, which is important in distinguishing between isotopes of the same element. Isotopes are atoms of the same element that have different numbers of neutrons. In this case, the potassium isotope with 19 protons and 21 neutrons is referred to as potassium-40 (written as (^{40}K)).
The mass number is significant in various applications, including nuclear chemistry and medicine, as it affects the stability of the nucleus. Potassium-40 is a naturally occurring isotope and is slightly radioactive, which makes it important for various scientific studies, including those related to radiometric dating and understanding potassium metabolism in living organisms.