Student Question

# Calculate the subatomic particles for isotopes: Al

## Expert Answers

Subatomic particles are small particles found in atoms. The three main subatomic particles are protons, neutrons, and electrons.

Isotopes are different forms of the same element. The isotopes of an element are different from one another because they have different numbers of neutrons. Because they have different numbers of neutrons, they also have different masses.

There are three main isotopes of aluminum. We can indicate the isotopes for aluminum by using two different isotope symbols as shown below.

Aluminum-26 OR `~^26_13Al`

Aluminum-27 OR `~^27_13Al`

Aluminum-28 OR `~^28_13Al` ` `

In the first version, the name of the element is followed by a dash and a number. The number is equal to the mass of the isotope.

In the second version, two numbers are written in front of the element symbol. The top number is equal to the mass of the isotope. The bottom number is equal to the atomic number of the element.

Calculating Protons, Neutrons, and Electrons:

• # Protons: The number of protons is always equal to the atomic number of the element. When you are using the second isotope symbol shown above, the atomic number is the bottom number. So, the number of protons is equal to the bottom number in the symbol. When you are using the first isotope symbol shown above, the atomic number is not indicated. In this case, you will need to use a periodic table to find the atomic number.
• # Electrons: If the isotope is neutral (i.e. does not have a charge), the number of electrons is also equal to the atomic number. So, the number of electrons is equal to the number of protons.
• # Neutrons: The mass number is indicated in both of the isotope symbols show above. The mass number is equal to the number of protons plus the number of neutrons. Therefore, the number of neutrons can be calculated by subtracting the number of protons from the mass number.

Each of the isotopes of aluminum would have the following numbers of protons, neutrons, and electrons.

Aluminum-26 OR : 13 protons, 13 electrons, 13 neutrons (26 - 13)

Aluminum-27 OR : 13 protons, 13 electrons, 14 neutrons (27 - 13)

Aluminum-28 OR : 13 protons, 13 electrons, 15 neutrons (28 - 13)

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