The atomic mass of copper is calculated by taking a weighted average of the masses of its isotopes, considering their relative abundances. Copper has two naturally occurring isotopes: ⁶³Cu and ⁶⁵Cu.
Understanding Isotopes and Atomic Mass
- Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons. They have the same atomic number but different mass numbers.
- Atomic Mass: The weighted average mass of all isotopes of an element, considering their relative abundances in nature. It's expressed in atomic mass units (amu).
Calculating Copper's Atomic Mass
Copper's two isotopes and their abundances are:
- ⁶³Cu: 69.15% abundance, mass = 62.9300 amu
- ⁶⁵Cu: 30.85% abundance, mass = 64.928 amu
The calculation involves multiplying the mass of each isotope by its fractional abundance (abundance percentage divided by 100) and then summing the results:
Atomic mass of Copper = (Abundance of ⁶³Cu × Mass of ⁶³Cu) + (Abundance of ⁶⁵Cu × Mass of ⁶⁵Cu)
Atomic mass of Copper = (0.6915 × 62.9300 amu) + (0.3085 × 64.928 amu)
Atomic mass of Copper = 43.50 amu + 20.05 amu
Atomic mass of Copper = 63.55 amu
Therefore, the average atomic mass of copper is approximately 63.55 amu. Note that this is an average; no single copper atom has this exact mass.
Step-by-Step Guide (As per Study.com):
- Identify Isotopes and Abundances: Determine the isotopes of the element and their relative abundances (percentages).
- Multiply Mass by Percentage: For each isotope, multiply its mass (in amu) by its abundance (expressed as a decimal).
- Sum the Results: Add up the results from Step 2. The sum is the average atomic mass of the element.
