In this lesson we will learn how atoms are defined by the number of protons they contain, as well as the number of neutrons.
By the end of this lesson you will be able to:
- Define atomic number.
- Define mass number.
- Compare isotopes of an element.
(Image: majcot, Adobe Stock)
- The number of protons in an atom is called the atomic number.
- Atomic Number = Number of Protons
- The number of protons plus the number of neutrons in an atom is called the mass number.
- Mass Number = Number of Protons + Number of Neutrons
- The atomic number of an element is fixed but the mass number can vary.
- Atoms that have the same atomic number (number of protons) but different mass numbers (number of neutrons) are called isotopes.
(Header image: Johannes Schneider, Wikimedia Commons)