The karat scale used to describe gold alloys is based on mass percentages. (a) If an alloy is formed that is 50 mol% silver and 50 mol% gold, what is the karat number of the alloy? Use Figure 12.18 to estimate the color of this alloy.
Ch.12 - Solids and Modern Materials
Chapter 12, Problem 126a
(a) What are the C—C—C bond angles in diamond?


1
Identify the structure of diamond, which is a three-dimensional network of carbon atoms.
Recognize that each carbon atom in diamond is sp3 hybridized, forming four single covalent bonds with other carbon atoms.
Understand that in an sp3 hybridized carbon, the bond angles are determined by the tetrahedral geometry.
Recall that the ideal bond angle in a tetrahedral geometry is 109.5 degrees.
Conclude that the C-C-C bond angles in diamond are approximately 109.5 degrees.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Tetrahedral Geometry
In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement. This geometry arises from the sp3 hybridization of carbon, where the bond angles between the carbon-carbon bonds are approximately 109.5 degrees. This spatial arrangement contributes to the strength and rigidity of the diamond structure.
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Bond Angles
Bond angles are the angles formed between two bonds that share a common atom. In the case of diamond, the bond angles between the carbon-carbon bonds are crucial for understanding its three-dimensional structure. The tetrahedral bond angles of 109.5 degrees ensure that the carbon atoms are optimally spaced, minimizing electron pair repulsion according to VSEPR theory.
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Crystal Lattice Structure
Diamond has a crystal lattice structure, which is a repeating pattern of atoms in three-dimensional space. This arrangement not only defines the bond angles but also contributes to diamond's exceptional hardness and thermal conductivity. The regularity of the lattice allows for uniform bond angles and distances, reinforcing the stability of the material.
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Related Practice
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Textbook Question
The karat scale used to describe gold alloys is based on mass percentages. (b) If an alloy is formed that is 50 mol% copper and 50 mol% gold, what is the karat number of the alloy? What is the color of this alloy?
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Open Question
Spinel is a mineral that contains 37.9% Al, 17.1% Mg, and 45.0% O, by mass, and has a density of 3.57 g/cm³. The unit cell is cubic with an edge length of 8.09 Å. How many atoms of each type are in the unit cell?
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