Isotopes

I. VIDEO ON ISOTOPES AND ATOMIC MASS

A. What is an Isotope?

B. How to Calculate Atomic Mass Practice Problems

C. Calculating Relative Abundance of Each Isotope

II. NOTES ON ISOTOPES AND ATOMIC MASS

ISOTOPE

Any two or more forms of an element where the atoms have the same number of

protons, but different number of neutrons within its nucleus.

ISOTOPES OF HYDROGEN

ISOTOPES OF LITHIUM

ATOMIC MASS

The weighted average mass of all the naturally occuring

isotopes of an element.

So when calculating the atomic mass of an element, one must take into consideration both the different isotopic forms of each isotopic form and their relative abundance.

FOR EXAMPLE

THE CALCULATION FOR THE ATOMIC MASS FOR OXYGEN WOULD BE

ATOMIC MASS OF OXYGEN =15.9994 amu

III. EXERCISES ON ISOTOPES AND ATOMIC MASS

1. Copper, a metal known since ancient times, is used in electrical cables and pennies, among other things. The atomic masses of its two stable isotopes 63Cu (69.09 %) and 65Cu (30.91%) are 62.93 amu and 64.9278 amu, respectively. Calculate the average atomic mass of copper. The relative abundances are given in parentheses.

2. The atomic masses of the two stable isotopes of boron 10B (19.78%) and 11B (80.22%) are 10.0129 amu and 11.0093 amu, respectively. Calculate the average atomic mass of boron.

3. The atomic masses of 6Li and 7Li are 6.0151 amu and 7.0160 amu, respectively. Calculate the natural abundances of these two isotopes. The average atomic mass of Li is 6.941 am.

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