Page 39 - Chemistry eBook

Atomic Mass/Mass Number
ATOMIC MASS/MASS NUMBER: Number of protons + neutrons in an atom
• Atomic mass tells you how heavy the atom is. Atomic mass can be expressed in different ways: 1. As a small number to the left of the
element’s symbol.
2. Following the element’s name, with a
“Don’t confuse
24Mg
Mg-24 atomic number!”
atomic mass with
dash before it.
To figure out the number of neutrons in an atom, follow this equation:
Atomic mass – atomic number = number of neutrons
(You can check the atomic number on Reffy. It never changes.) How do we know the atomic mass the atomic number of an element? Ask Reffy!!
Atomic mass can change. Atomic number NEVER changes.
UNIT 2: ATOMIC STRUCTURE © 39