Unformatted text preview: CHM CHM 25 Chapter 11 Chapter 11- Part I The The Chemistry of Solids
Spring 2009 Spring, 2009 Prof. R.S. Miller Alloys homogeneous Alloys – homogeneous mixture of metals
Gold rings – most alloys (except 24 karat) – Au + Pd, Ag, or Cu. ◦ 14K gold contains 14 parts gold and 10 parts of another metal(s), making it 58.3% gold. Steel – Fe, C, Cr (18% Cr makes stainless steel). Brass – Cu & Zn – resulting mat’l is harder than two elemental components. Bronze – Sn and Cu. Alloy uses: transportation mat’l, construction, sports equipment. Cu bonding models: Cu Metallic Metallic Bonds
Band Band theory is an extension of MO is theory that describes bonding in solids. Bands of orbitals that are filled or partially filled by valence electrons are called valence bands. Hi Higher-energy unoccupied bands in which electrons are free to migrate are called called conduction bands. Band Band Theory
As As the half-filled 4s orbitals of an increasing number of Cu atoms overlap, their energies their are split into a half-filled valence band. Electrons can move from the filled half (purple) to the slightly higher energy upper half (red), gy where they are free to migrate from one empty orbital to another. Metalloids Metalloids – physical prop of metals & chemical prop of nonmetals Band Band Gap
The energy gap between the valence and conduction bands is called the band gap. A semiconductor is a substance whose conductivity can be made to vary over several orders of magnitude by altering its chemical composition. A n-type semiconductor contains excess yp electrons contributed by electron-rich dopant atoms. (Si doped w/ P). A p-type semiconductor contains electron-poor dopant atoms (Si doped w/ Ga). Metallic Metallic Crystals stacking patterns http://www.wwnorton.com/college/chemistry/gilbert2/contents/ch11/c hemtours.asp Stacking Stacking Patterns A crystalline solid - ordered array of atoms ions or atoms, ions, or molecules. Hexagonal closest-packed (hcp) – hexagonal unit cell have an ababab . . . stacking pattern. Cubic closest packed (ccp) - facecentered cubic unit cells have an abcabcabc abcabcabc . . . stacking pattern. stacking
http://tannerm.com/AnimatedAtoms/closest_packing.htm Stacking Stacking Patterns
The unit cell is the basic repeating unit of the arrangement of atoms, ions, or molecules in a crystalline solid. A face-centered cubic (fcc) unit cell has the same kind of particle (atoms, ions, or molecules) at the 8 corners of a cube and at the center of each face (ccp arrangement). Summary Summary of Crystal Structures Examples Examples of Unit Cells Unit Unit Cells Contributions of Atoms to Cubic Unit Cells
Position of Atoms in Unit Cell Center Face Corner Contribution to Unit Cell 1 1/2 1/8 Unit-Cell Type bcc Fcc fcc, bcc, simple bcc simple cubic Atoms Atoms in a simple cubic unit cell
In the simple cubic cell there are only the 8 atoms at the corners.
1/8 x 8 = 1 atom in cell Atoms in bcc unit cell ll
In bcc, 8 atoms at the corners and 1 in center
(1/8 x 8) + (1) = 2 atoms in the cell Atoms Atoms in fcc unit cell
In fcc, 8 atoms atoms at the corners, 1 in center of each of the 6 faces.
(1/8 x 8) + (1/2 x 6) = 4 atoms in atoms the cell Density Density of Au
Gold crystallizes in a fcc w/ edge length = 407 pm. Calculate the density of Au in g/cm g/cm3. Alloys Alloys
An alloy is a blend of a host metal and one or more other elements which are added to change the properties of the host metal. Ores are naturally occurring compounds or mixtures of compounds from which elements elements can be extracted. Bronze Effect of Carbon Content on the Properties of Steel
Carbon Content (%) 0.05 - 0.19 0.20 - 0.49 0.5 - 3.0 Designation Low Carbon Medium Carbon High Carbon Properties Malleable, ductile High strength Hard but brittle Used to Make Nails, cables Construction girders Cutting tools ...
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- Spring '06
- Alloy, atoms atoms, Unit Unit Cells