Determining the
NUMBER of
Protons
Electrons
and
Neutrons
in Atoms, Ions, and Isotopes
NUMBER of PROTONS
• For any given element, the number of
protons equal the atomic number
12
Mg
24.30
ATOMIC NUMBER
Examples
Element
Carbon
Iron
Nickel
Iodine
Barium
Atomic Number
Protons
6
6
26
26
28
28
53
53
56
56
NUMBER of ELECTRONS
• For any given element, the number of
electrons equal the protons.
12
Number of protons
Mg
or
24.30
Atomic Number
Examples
Atomic
Element Number Protons Electrons
Carbon
Iron
Nickel
Iodine
Barium
6
6
6
26
26
26
28
28
28
53
53
53
56
56
56
NUMBER of NEUTRONS
• For any given element, the number of
neutrons plus protons equal the mass
number.
12
Mg
24.30
ATOMIC MASS
Ions
• Substances that have a positive or
negative charge.
• Created by the change in
ELECTRONS.
• Protons and Neutrons are determined
in the same way as atoms.
Number of Electrons in Ions
• The number of electrons may be
calculated as:
2S
Charge of the ion
16 - (-2) = 18
Examples
Ion
Atomic
Number
Number of
Electrons
Na1+
11
10
Br1-
35
36
Al3+
13
10
O2-
8
10
Isotopes
• Substances that have the same atomic
number but different mass numbers
• Created by the change in NEUTRONS.
• Protons and Electrons are determined
in the same way as atoms.
Number of Neutrons in Isotopes
• The number of neutrons may be
calculated as:
H-1 H-2 H-3
Mass Number
Examples
Mass
Number
Number of
Neutrons
C-12
12
6
C-14
14
8
U-238
238
146
U-235
235
143
Isotope