Aim: I.O.SWBAT : 1)Distinguish between crystalline and amorphous solids.

Aim:

I.O.SWBAT: 1)Distinguish between crystalline and amorphous solids. 2) Predict the type of solid. 3) Predict different solids general property.

Motivation:

Do-Now: Complete the hand-out.

Do-Now: Give the phase of each of the following substances at room temperature.

a) Aluminum b) Plastic

Solids

• Have both definite structures and definite volume.

• There are two general groups of solids:– Crystalline solids: Particles are in

highly ordered arrangement.

Crystal structures are determined experimentally by X-Ray Diffraction.

Find a repeating pattern.

Crystalline Lattice

Repeating pattern of particles

Lattice point

Unit cell: the smallest repeating unit in the pattern in 3-D.

In the primitive unit cell, the atoms at the corners are cut because only 1/8 belongs to that cell. The rest of the atom belongs to neighboring cells.

Primitive unit cell

1/8 of 8 atoms (ions) = 1 atom per cell

Primitive unit cell

Body-centered cubic

Body-centered cubic cell (bcc)

1/8 of 8 atoms + 1 in the center 2 atoms per cell

Face-centered cube (fcc)

Each atom at the center of each face is shared with another cell.

1/8 of 8 atoms +1/2 of 6 atoms 4 atoms per cell

How many atoms are within the unit cell below?

SUMMARY

Atoms at the corners = 1/8

Atoms at an edge = 1/4

Atoms at a faces = 1/2

Atoms at the center = 1

– Amorphous solids: No particular order in the arrangement of particles. (no crystal lattice)

– Have NO definite melting pts.

Substance Melting pt (oC)

Bond type

NaCl 801

C12H22O11 185

Diamond 3550

Fe 1530

Al 620

Complete the following chart.

TYPE OF SOLIDS1. Molecular solids:Molecules are held together by weak intermolecular forces. (dipole-dipole, london dispersion, H-bond) PROPERTIES: Soft, low m.p.(usually below 200oC) Ex. Sugar, graphite

2. Covalent network solids:• Contain no discrete molecular units. • The atoms in the network solid are held together by covalent bonds with neighboring atoms. • The result is a single extended network.

PROPERTIES: Hard, high m.p. Ex. Diamond,SiO2(sand, quartz), SiC, BN

Diamond:• Bond angle = 109o

• Tetrahedral shape • sp3 Hybridization• Non-conductor of electricity• 3 dimensional

Graphite:• Bond angle = 120o

• Trigonal planar shape

• Sp2 hybridization• Conductor of electricity• 2 dimensional

*Graphite can conduct electricity because of delocalized electrons (-bonds) in the benzene ring.

Allotropes: Different forms of the same element that differ in bonding. Ex. C: graphite, diamond O: O2, O3 (ozone)

3. Metallic solids:• Covalent bonds between positive ions immersed in a “sea” of delocalized valence electrons.• Hardness and m.p. depend on the number of valence electrons. (Wide range of hardness and m.p.)

4. Ionic solids:• Ions held together by strong electrostatic attraction.• Melting pts. depend mostly on the charge of the ions.

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QkQ 21

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HW# 40

Do-Now: In terms of kinetic energy, explain why super critical fluids cannot be liquefied by increasing pressure.