Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2015

Lecture Notes 39: 4 May

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Solids, cont.

Bragg Equation

Crystal (Solid) Structure

Crystal Structure (overheads)

Lattice

Unit Cell (demo with cork ball cells)

Crystal lattice

3 kinds of cubic lattice: simple cubic, body-centered cubic (bcc), and face-centered cubic (fcc). (Figure 10.9, p 460 of Zumdahl)

The images below show the so-called cannon ball stacking in close-packing. Note that the stack is a direct result of the HCP lattice shown in the image above, where just the top ball and the next layer of three balls are darkened. Can you discern the next (triangular) layer in the diagram which cooresponds to the third layer down in the pictures below?

Types of Solids

Metallic solids: these are different in that they have ions at the lattice points in a "sea" of shared electrons (Figures 10.18–20, p 469–70 of Zumdahl). In metals that are very hard, such as chromium, the ions are also covalently bonded to each other.

Network (or covalent) solids - Carbon as example: carbon has allotropes (different physical forms of the same element) all of which have many atoms linked together in covalent networks, and two of which are covalent solids: (Figure 10.22, 24, 24, p 471–4 of Zumdahl)

Diamond (covalent solid) - each atom in the bulk solid is covalently bonded to four others in a tetrahedral arrangement. This is the secret to diamond's great hardness: to break a piece off many strong covalent bonds must be broken.

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© R A Paselk

Last modified 4 May 2015