An atom of bromine has an atomic number of 35 and a mass number of 81. What is the total n… — Armed Services Vocational Aptitude Battery (ASVAB)

An atom of bromine has an atomic number of $35$ and a mass number of $81$ . What is the total number of neutrons contained in its nucleus?

The nucleus contains

46

neutrons.

The mass number of an atom is the total count of protons and neutrons in the nucleus (

A = \text{protons} + \text{neutrons}

). Given that the atomic number is

35

(protons =

35

) and the mass number is

81

, the number of neutrons is calculated as

81 - 35 = 46

Identify the given values from the problem statement.

Atomic number (

Z

) =

35

(which equals the number of protons); Mass number (

A

) =

81

(total nucleons in the nucleus).

The atomic number defines the number of protons, and the mass number represents the sum of protons and neutrons.

Apply the relationship between mass number, protons, and neutrons:

\text{Mass Number } (A) = \text{Protons } (Z) + \text{Neutrons } (N)

N = A - Z

To find the unknown number of neutrons, rearrange the standard subatomic relationship.

Substitute the known integer values into the equation:

N = 81 - 35

N = 46

Subtracting

35

from

81

gives the total number of neutrons in the nucleus.

The mass number (

A

) of an atom equals the sum of its protons (

Z

) and neutrons (

N

). The number of neutrons is found by subtracting the atomic number from the mass number (

N = A - Z

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