Chemistry In Focus

6th Edition
Tro + 3 others
ISBN: 9781305084476



Chemistry In Focus

6th Edition
Tro + 3 others
ISBN: 9781305084476
Textbook Problem

40 K is used to measure the age of Earth. Determine the number of protons and neutrons in 40 K .

Interpretation Introduction


The number of protons and neutrons in 40K are to be determined.

Concept Introduction:

 An atom consists of a nucleus and extranuclear space. The nucleus of an atom is composed of protons and neutrons while the extra nuclear space contains electrons.

 The isotopes of an element are the species which contain the same number of protons but a different number of neutrons so they are the variants of the same element. The mass number of an atom is represented by A and because the atomic number is equal to the number of protons, it is represented by Z.

 So, the number of neutrons can be calculated as follows:

Number of neutrons=Mass number-Atomic numberN=A-Z


The atomic number of K is 19 and hence, the number of protons is also 19. Because atomic number represents the number of protons.

The mass number of potassium is 40 and its atomic number 19. So, the number of neutrons is calculated as follows:

Number of neutrons=Mass numberAtomic number x

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