Question

a student wants to draw a model of an atom. which statement describes how to find the number of neutrons to include in the model? (1 point)
subtract the atomic number from the mass number.
add the number of electrons to the number of protons.
add the atomic number and the mass number.
subtract the number of electrons from the number of protons.

Explanation:

The mass number of an atom is the sum of protons and neutrons. The atomic number is the number of protons. So, to find the number of neutrons, we use the formula \( \text{Number of neutrons}=\text{Mass number}-\text{Atomic number}\).

• For the option “Add the number of electrons to the number of protons”: In a neutral atom, the number of electrons equals the number of protons. Adding them gives \(2\times\) number of protons, not the number of neutrons.
• For the option “Add the atomic number and the mass number”: This gives \( (\text{Protons})+(\text{Protons}+\text{Neutrons}) = 2\times\text{Protons}+\text{Neutrons}\), not the number of neutrons.
• For the option “Subtract the number of electrons from the number of protons”: In a neutral atom, this gives \(0\) (since number of electrons = number of protons in a neutral atom), which is not related to the number of neutrons.

Answer:

Subtract the atomic number from the mass number.