Determining An Isotope

Determining an Isotope

Mass Numbers

• Atomic Mass=Protons + Neutrons

• The identity is based on the number of protons.

• Given: Iodine-131, Iodine-129, Iodine-127

• Let’s determine the number of neutrons.

Protons

• Where is Iodine on the periodic table?

• Element number 53.

• All Iodine isotopes have the same exact number of protons, 53.

• All Iodine isotopes also have 53 electrons.

Neutrons

• Let’s determine the number of neutrons.

• First, Iodine 131.

• 131 is protons + neutrons.

• 131-53 protons=78 neutrons.

• Iodine 130.

• 130-53=77 neutrons

• Iodine 127

• 127-53=74 neutrons

Finding the number of protons

• Given a substance with a mass of 42 amu.

• We are told this atom has 22 neutrons.

• What is the identity?

• Take the total mass of 42. This is 42 protons and neutrons.

• 42-22 neutrons=20 protons

How to solve for the identity

• The atomic number is also the same as the number of protons.

• The atomic number is like a permanent address. No matter what you do to the house, it will always have the same foundation (protons) and always have the same location (atomic number).

• 20 protons=Atomic # 20, Calcium