Question

Elements occur in a number of isotopic forms. In this problem, you will learn about the notation used to distinguish different isotopes.

Part A

How many protons Z and how many neutrons N are there in a nucleus of the most common isotope of silicon, 28/14Si?

Separate your answers with a comma.

Z, N =

Answer 1

• Number of protons, Z = 14
• Number of neutrons, N = 14

Step-by-step explanation:

1) About isotopes:

Isotopes are different kind of atoms of the same element. Hence, they have the atomic number (Z), which is the number of protons, the same number of electrons (talking about to neutral atoms, not ions), and different number of neutrons N).

This is, it is the number of neutrons what distinguish different isotopes of an element.

2) About the notation used to distinguish different isotopes:

A superscript and a subscript, both to the left of the chemical symbol of the element, are used to distinguish different isotopes:

A ←------------- This superscript tells the mass number of the isotope

X ←--------- This is the chemical symbol of the element

Z ←-------------- This subscript is the atomic number of isotope

In our case, the notiation for the isotope of silicon is: ²⁸₁₄ Si

So, we have:

• 28 is the mass number (A)
• 14 is the atomic number (Z)
• Si is the chemical symbol.

Now, you can answer the questions of the part A:

• Number of protons: Z = 14

• Number of neutrons N:

mass number = number of protons + number of neutrons

A = Z + N

⇒ N = A - Z = 28 - 14 = 14

In conclusion:

• Number of protons, Z = 14
• Number of neutrons, N = 14