Determining the Determining the NUMBER ofNUMBER of

ProtonsElectrons

and Neutrons

in Atoms, Ions, and Isotopes

NUMBER of PROTONSNUMBER of PROTONS• For any given element, the number of

protons equal the atomic number

12

Mg

24.30

ATOMIC NUMBER

ExamplesExamples Element Atomic Number Protons

CarbonIronNickelIodineBarium

6 6

26 26

28 28

53 53

56 56

NUMBER of ELECTRONSNUMBER of ELECTRONS

• For any given element, the number of electrons equal the protons.

12

Mg

24.30

Number of protons

or

Atomic Number

ExamplesExamples

ElementAtomicNumber Protons Electrons

CarbonIronNickelIodineBarium

6 6

26 26

28 28

53 53

56 56

6

26

28

53

56

NUMBER of NEUTRONSNUMBER of NEUTRONS• For any given element, the number of neutrons

plus protons equal the mass number.

12

Mg

24.30 ATOMIC MASS

IonsIons• 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 IonsNumber of Electrons in Ions

• The number of electrons may be calculated as:

S2-

16 - (-2) = 18

Charge of the ion

ExamplesExamplesIon Atomic

NumberNumber ofElectrons

Na1+

Br1-

Al3+

O2-

11

35

10

36

13 108 10

IsotopesIsotopes• 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 IsotopesNumber of Neutrons in Isotopes

• The number of neutrons may be calculated as:

H-1 H-2 H-3 Mass Number

ExamplesExamplesIsotope

MassNumber

Number ofNeutrons

C-12

C-14

U-238

U-235

12

14

6

8

238 146

235 143