Chem-To-Go Lesson 6Unit 2

ISOTOPES AND ATOMIC

MASS

QUICK REVIEW

PROTON NEUTRON ELECTRON

• Has mass• Found in the

nucleus

• Has mass• Found in the

nucleus

• Has no mass• Found outside

the nucleus

ISOTOPE ILLUSTRATION

𝐇𝟏𝟏 𝐇𝟏

𝟐 𝐇𝟏𝟑

Hydrogen-1

Hydrogen-2

Hydrogen-3

Why are all three atoms considered to be hydrogen?Definition of Isotope: Atoms of the same element

that have different masses because of differing numbers of neutrons (therefore different mass numbers)

PREVALENCE OF ISOTOPES

All of these blocks are called Legos,

but they are not all identical to one

another.Most

elements have

several isotopes.

ATOMIC MASS

If there are THREE different types of magnesium atoms, which ONE is

represented on the periodic table?

• Answer: None! The block represents the average magnesium atom.

• Huh? No magnesium atom actually weighs 24.3050 amu. All of the different types of magnesium atoms were averaged, and an average Mg atom weighs 24.3050 amu.

Atomic Mass = [(decimal abundance)(mass)] + [(decimal abundance)(mass)] + [(decimal abundance)(mass)] + …

CALCULATING ATOMIC MASS

Atomic Mass = [(decimal abundance)(mass)] + [(decimal abundance)(mass)] + [(decimal abundance)(mass)] + …

CALCULATING ATOMIC MASS