Only two isotopes of copper occur naturally: ⁶³Cu (atomic mass = 62.9296 amu; abundance 69.17%) ⁶⁵Cu (atomic mass = 64.9278 amu; abundance 30.83%). Calculate the atomic weight (average atomic mass) of copper.

Verified step by step guidance

1. Identify the atomic masses and their respective abundances for each isotope. For ⁶³Cu, the atomic mass is 62.9296 amu and the abundance is 69.17%. For ⁶⁵Cu, the atomic mass is 64.9278 amu and the abundance is 30.83%.
2. Convert the percentage abundances into decimal form by dividing each by 100. For ⁶³Cu, 69.17% becomes 0.6917. For ⁶⁵Cu, 30.83% becomes 0.3083.
3. Multiply the atomic mass of each isotope by its corresponding decimal abundance. For ⁶³Cu, multiply 62.9296 amu by 0.6917. For ⁶⁵Cu, multiply 64.9278 amu by 0.3083.
4. Add the products from the previous step to find the weighted average of the atomic masses. This sum will give you the average atomic mass of copper.
5. The result from the previous step is the atomic weight of copper, expressed in atomic mass units (amu).

Key Concepts

Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For example, copper has two stable isotopes, 63Cu and 65Cu, which differ in their neutron count and thus their atomic mass.

Atomic Weight

Atomic weight, or average atomic mass, is the weighted average of the masses of an element's isotopes, taking into account their relative abundances. It is calculated by multiplying the mass of each isotope by its abundance (expressed as a fraction) and summing these values.

Weighted Average Calculation

To calculate a weighted average, each value is multiplied by its weight (or proportion), and the results are summed and divided by the total of the weights. In the case of copper, the atomic weight is calculated by summing the products of each isotope's mass and its abundance, providing a more accurate representation of the element's mass in nature.