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Unit 8 Chapter 10 Notes Liquids and Solids. Three States of Matter. Section 10.1: Intermolecular forces What is a condensed state? Intermolecular forces: Do molecules change as a substance changes state? Why do substances change state?. Dipole-dipole interaction:.
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Unit 8 Chapter 10 Notes Liquids and Solids
Section 10.1: Intermolecular forces What is a condensed state? Intermolecular forces: Do molecules change as a substance changes state? Why do substances change state?
London Dispersion Forces- Why do dispersion forces exist? Polarizability-
Section 10.2: The Liquid State Why does liquid bead up on surfaces? Surface tension:
Capillary action: When does a convex meniscus form? Viscosity:
Crystalline solids are composed of highly regular arrangement of their components Amorphous solids have a considerable amount of disorder in their structures What is the difference between crystalline solids and amorphous solids?
What is a lattice? • A lattice is a 3-D system of points designating the positions of the components (atoms, ions, or molecules) that make up the substance • The smallest repeating unit of the lattice is called the unit cell
What is X-ray diffraction used for? • It is used to determine the structure of crystalline solids
The Bragg Equation xy + yz = nλ xy + yz = 2d sin Ө nλ = 2d sin Ө
Sample Exercise 10.1 X-rays of wavelength 1.54 Å were used to analyze an aluminum crystal. A reflection was produced at Ө = 19.3 degrees. Assuming n = 1, calculate the distance d between the planes of atoms producing this reflection. nλ (1)(1.54 Å) 2 sin Ө (2)(0.3305) d = = = 2.33 Å = 233 pm
Types of Crystalline Solids • Ionic solids (represented by sodium chloride) have ions at the points of the lattice that describes the structure of the solid
cont. • Molecular solids (represented by sucrose) have discrete, covalently bonded molecules at each of its lattice points • Ice is a molecular solid that has an H2O molecule at each point
cont. • Atomic solids have atoms at the lattice points that describe the structure of the solid • One example is carbon, which exists in the forms of graphite and diamond
Subgroups of atomic solids • In metallic solids, a special type of delocalized non-directional covalent bonding occurs • In network solids, the atoms bond to each other with strong directional covalent bonds that lead to giant molecules, or networks, of atoms • In the Group 8A solids, the noble gas elements are attracted to each other with London dispersion forces
What structure do metals form? • Metal atoms are as closely packed as possible in a cubic or hexagonal shape • The atoms are in layers where each atom is surrounded by 6 others • Atoms of the next layer rest in the depressions formed by the first layer
Cubic Structure • Has abca • Every forth atom layer is directly above the first • Face centered unit cell
Hexagonal Structure • aba structure • in every other layer the atoms are directly above the first
How can you calculate density of a metal using unit cell? (using Ag as example) • First determine the number of atoms in the unit (8x1/8[corners])+(6x1/2[face centered])=4atoms • The diagonals equals four times the atomic radius (atomic radius of Ag= 144pm= 1.44x10-12) 4r=5.76x10-8cm • Using the Pythagorean Theorem each side of the unit cell =4.07x10-8cm • (4.07x10-8) 3=6.74x10-23)cm3 • Density=mass/volume= ((4 atoms) (107.9g/mol) (1mol/6.022x1023 atoms)) / (6.74x10-23 cm3) =10.6g/cm3
What is the electron sea model? • Metal cations surrounded by a “sea” of electrons • What is the band model? • Electrons travel around in the metal crystal in orbitals formed by valence electrons
Figure 10.20 A Representation of the Energy Levels (Bands) in a Magnesium Crystal
What properties of metals are explained by metallic bonding? • Properties of metals: malleable, good conductors, and ductile • Electrons are free to move around transmitting heat and electricity • Atoms are easily moved in relation to each other but hard to separate
What are alloys? • A substance that contains a mixture of elements and metallic properties • Substitutional alloy: host metal atoms are replaced by another metal ex. brass • Interstitial alloy: formed when small atoms occupy spaces between atoms ex. steel
Section 10.5: Carbon and Silicon: Network Atomic Solids • Network Solids: • What is the difference between diamond and graphite? • Silica-
Figure 10.23 Partial Representation of the Molecular Orbital Energies in (a) Diamond and (b) a Typical Metal
Figure 10.24 a & b The p Orbitals (a) Perpendicular to the Plane of the Carbon Ring System in Graphite can Combine to Form (b) an Extensive pi Bonding Network
Silicates • Why is silicon dioxide so different from carbon dioxide? • Silicates: • Ceramics:
Figure 10.26 The Structure of Quartz (Empirical Formula SiO2)
Figure 10.28 a & b Two-dimensional Representations of (a) a Quartz Crystal and (b) a Quartz Glass
Semiconductors • Semiconducting element: semiconductor: • N- type semiconductor- • P- type semiconductors – • P-N junction- • Rectifier -
Figure 10.29 a & b (a) A Silicon Crystal Doped with Arsenic (b) A Silicon Crystal Doped with Boron
Figure 10.30 a & b Energy-Level Diagrams for (a) an N-Type Semiconductor and (b) a P-Type Semiconductor
Figure 10.31 The P-N Junction Involves the Contact of a P-Type and an N-Type Semiconductor
Figure 10.32 A Schematic of Two Circuits Connected by a Transistor
What are the characteristics of molecular solids? • Strong covalent bonding within molecules • Weak forces between molecules
Would you expect a molecule that is non-polar to be gas or solid or liquid at room temperature? • for small molecules- gas. • For large molecules- liquid or solid • Because of increasing London dispersion forces
What are the differences between covalent bonds within the molecules and the forces between the molecules? • Covalent bonds are stronger • Intermolecular forces are weaker • Requires less energy to break the intermolecular bonds
