Question

An atom of Bismuth (Bi) having an atomic mass of 209 amu has an atomic numbr of 83. How many neutrons are present in this atom of Bismuth? (show the calculations)​

Answer 1

126

Step-by-step explanation:

To calculate for neutron #, subtract atomic # from atomic mass.

t hus 09- 83= 126

Answer 2

There are 126 neutrons in the bismuth atom.

Step-by-step explanation:

Pre-Solving

We are given that a Bi atom has an atomic mass of 209 amu and an atomic number of 83.

We want to find how many neutrons the bismuth atom has.

Solving

The atomic mass of an atom is equal to the mass of the protons + mass of neutrons (n.b. the electrons are part of the mass too, however they are very, very small. Therefore, we tend to count the mass of the electrons as 0 when calculating the atomic mass).

Recall that protons and neutrons both have a mass of about 1 amu.

Also recall that the proton number is also the atomic number. Because of this, the bismuth atom has 83 protons. And since that protons have a mass of about 1 amu, the atomic mass of the protons will be:

83 protons ×
`(1 amu)/(1 proton)` = 83 amu

That means that if the atomic mass is 209 amu, it is equal to the proton mass (83 amu) + an unknown mass of neutrons (let's say it is x amu).

As an equation, it will be:

83 + x = 209

Subtract 83 from both sides.

x = 126

This means that the neutrons will weigh 126 amu.

Since every neutron is about 1 amu, the amount of neutrons will be:

126 amu ×
`(1 neutron)/(1 amu)` = 126 neutrons