Download Atomic Number and Mass Number

Atomic Number and Mass Number:
 Atomic Number: Number of protons in an atom; This number identifies the element.
 Mass Number: Number of protons and neutrons in an atom.
 To determine the mass number, you must round the average atomic mass to the
nearest whole number

12
 Atomic Number
Mg
 Element Symbol
Magnesium
 Element Name
24.305
Average Atomic Mass
 Calculating Number of Neutrons:
Number of Neutrons = Mass Number – Atomic Number
 If the atom is neutral, the number of protons and electrons are equal.
 Example:
12 eMagnesium
12 p+
12 n
 Example:
Lead
82 e82 p+
125 n