Isotopes

Isotopes• Isotopes are atoms that have the same

number of protons but different numbers of neutrons

• Most elements in the first two rows of the periodic table have at least 2 isotopes with one being more common than the other

• In nature, elements are almost always found as a mixture of isotopes

Hydrogen Deuterium Tritium

•For example, the most common isotope of hydrogen has no neutrons at all

•There's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.

Neutron

Proton

Isotopes of Hydrogen

Most common isotope

• To identify an isotope more specifically, chemists add a number after the elements name.

ex. Carbon-11 Carbon-12 Carbon-14• This number is called the isotope’s mass number and

is the sum of the isotope’s number of protons and neutrons.

• For example, an atom with 17 protons and 20 neutrons has a mass number of 37.

More fun with Isotopes

Q. What is the mass of the Nitrogen isotope with 7 protons and 12 neutrons?

A. Nitrogen-19

iodine-128

potassium-40

75

21

53

19

53

19

Atom Protons Electrons Neutrons

Examples

Isotope Symbols

141

56

Mass number

Atomic number

ChargeBa2+

How many protons, neutrons, and electrons are present?

5626STEP 1: The atomic number in the lower left corner = 26 protons. The difference between the mass number and the atomic number is 56 – 26 = 30 neutrons

STEP 2: The charge on the ion, 2+ shows us that there are 2 more protons than electrons, indicating that there are 24 electrons.

Fe 2+

Isotope Symbols

141

56

Mass number

Atomic number

ChargeBa2+Step 1) 141- 56= 85 neutronsStep 2) 56 electrons -2 = 54 electrons