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Ch.2 - Atoms, Molecules, and Ions
All textbooksBrown 14th EditionCh.2 - Atoms, Molecules, and IonsProblem 35
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Chapter 2, Problem 35

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.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.
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Isotopes

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.
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Atom Structure

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.
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Average Rate Calculation Example
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Related Practice
Textbook Question
Without doing any detailed calculations (but using a periodic table to give atomic weights), rank the following samples in order of increasing numbers of atoms: 0.2 mol PCl5 molecules, 80 g Fe2O3, 3.0 3 1023 CO molecules.
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Textbook Question

(a) What isotope is used as the standard in establishing the atomic mass scale?

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Textbook Question

(b) Why is the atomic weight of carbon reported as 12.011 in the table of elements and the periodic table in the front inside cover of this text?

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Textbook Question

(a) Thomson's cathode-ray tube (Figure 2.4) and the mass spectrometer (Figure 2.11) both involve the use of electric or magnetic fields to deflect charged particles. What are the charged particles involved in each of these experiments?

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Textbook Question

Consider the mass spectrometer shown in Figure 2.11. Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (a) The paths of neutral (uncharged) atoms are not affected by the magnet.

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Textbook Question

Consider the mass spectrometer shown in Figure 2.11. Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (b) The height of each peak in the mass spectrum is inversely proportional to the mass of that isotope.

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