Polymer Chemistry Quiz

Chemistry of Engineering Materials: Metals

• Metals are elements, compounds, or alloys that conduct electricity and heat well.
• Metals are typically solids at room temperature, except for mercury.
• Metals are characterized by bright luster, hardness, the ability to resonate sound, and are excellent conductors of heat & electricity.
• Metals are typically solids at room temperature, except for mercury and gallium (sometimes liquid at higher temperatures).
• Metals are characterized by the ability to be hammered into sheets (malleability).
• Metals also have the ability to be drawn into wires (ductility).

Learning Objectives

• Introduce metals
• Describe the occurrence and abundance of metals in the Earth's crust
• Explain the metallurgical processes
• Explain the Band Theory of Electrical Conductivity
• Discuss the periodic trends of metals and their reactivity

Metal

• Metals are elements, compounds, or alloys that conduct electricity and heat.
• Their crystal structures determine their specific properties.

Metal (cont.)

• With the exception of hydrogen, elements that form positive ions during chemical reactions are called metals.
• Metals are solids under normal conditions, except for mercury.

Metals on Periodic Table

• A periodic table is presented identifying metals in various groups.

Physical Properties of Metal

• State: Most metals are solids at room temperature, except for mercury. Gallium is liquid at higher temperatures.
• Luster: Metals reflect light from their surface and can be polished.
• Malleability: Metals can be hammered into thin sheets.
• Ductility: Metals can be drawn into wires.
• Hardness: All metals are hard, except sodium and potassium which are soft and can be cut with a knife.
• Valency: Metals typically have 1 to 3 electrons in their outermost shell..
• Density: Metals have high density, with Iridium and Osmium having the highest. Lithium has the lowest.
• Melting and Boiling Points: Metals generally have high melting and boiling points, except mercury and sodium/potassium.

Chemical Properties of Metal

• Electropositive Character: Metals tend to have low ionization energies, losing electrons when undergoing chemical reactions. They usually do not accept electrons.

  • Alkali metals: Always +1 (lose the s-subshell electron).
  • Alkaline earth metals: Always +2 (lose both s-subshell electrons).
  • Transition metals: Ion charges vary (lose s and some d-subshell electrons).

• Chemical reactions are shown, illustrating oxidation states of metals (Na, Mg, Al).

Occurrence of Metal

• Most metals come from minerals.
• A mineral is a naturally occurring substance with a range of chemical compositions.
• An ore is a mineral deposit concentrated enough for economical metal recovery.
• Metals exist in various forms—within Earth's surface, as seawater ions, and in the ocean floor.
• Important metals are found in several different forms, and in varying concentrations.
• Representative minerals are given.
  • Examples of minerals—clay; bauxite
• Some metals are most readily found in seawater.

Metallurgy

• Metallurgy involves separating metals from their ores.
• This includes preparation, production, and purification.
• Preparation: Separation of desired metal from gangue/waste material
  • Methods include flotation, magnetic separation and amalgamation.

Production of Metals

• Processes for metal purification
  • Chemical reduction
  • Electrolytic reduction
  • Pyrometallurgy

Production of Metal (cont.)

• Specific examples of metal production, including iron.

Steelmaking

• Steel is an alloy of iron with small amounts of carbon and various other elements.
• Steelmaking involves oxidation processes to remove impurities.
• The basic oxygen process is a widely used simplification.
• Flux removes oxidized impurities.
• The cooling rate of the molten steel, called tempering, adjusts the carbon content and final product properties.
• A table with different steel types and their compositions.

Purification of Metals

• Metals require further treatment to remove impurities after reduction.
• Distillation, electrolysis, and zone refining are common purification methods.

Band Theory of Electrical Conductivity

• In solid-state physics, band theory describes the possible allowed energy ranges (bands) for electrons within solids.
• The theory postulates the existence of energy bands for electrons (allowed & forbidden bands).
• Band theory explains how electrons move in solids which can be used to understand conductivity.

Band Theory (cont.)

• Overlapping molecular orbitals produce bands in solids—valence band (low energy) & conduction band (higher energy)
• Band gap separating valence & conduction band; negligible gap = good conductor; large gap = insulator
• Metals (no band gap) are good electrical conductors.
• Semiconductors have a small band gap which causes their conductivity to be controlled by extrinsic factors.

Semiconductors

• Semiconductors can normally conduct electricity at high temperatures or when combined with other elements.
• Group 4A elements are semiconductors (esp silicon & germanium).

Semiconductors (cont.)

• Doping semiconductors can raise their conductivities.
• There are two doped categories—n-type (negative charge carriers) & p-type (positive charge carriers).

Alkali Metals

• Alkali metals are elements in group 1.
• They are silvery, cut easily with a knife, and have low density.
• Hydrogen doesn't always exhibit alkali metal properties.
• The word "alkali" comes from Arabic; meaning "from ashes".
• Alkali metals react with water readily, forming alkaline solutions.

Alkaline Earth Metals

• Alkaline earth metals are Group 2 elements.
• They are less reactive than alkali metals.
• They have a higher melting point than alkali metals, and are harder.
• The chemistry of radium is less well-studied due to its radioactivity.
• Emerald is a prominent mineral that contains beryllium.

Aluminum

• Aluminum is the most abundant metal in the Earth's crust.
• Bauxite (Al2O3 • H₂O) is its primary ore.
• Other related minerals include orthoclase, beryl, cryolite, and corundum.

Transition Metals

• Transition metals occupy groups 3-12, with variable oxidation states.
• They generally have incompletely filled d subshells that can be responsible for the colorful complexes & compounds they form.
• Transition metals often serve as catalysts in chemical reactions—without being consumed in the process.

Properties of Transition Metals

• Physical properties of transition metals are similar:

  • good conductors of heat and electricity.
  • can be hammered or bent into shape easily.
  • high melting points (mercury is an exception).
  • usually hard and tough
  • high densities

• Chemical properties of transition metals are more variable.

  • less reactive than alkali metals
  • form colored ions in compounds with different charges.
  • some are very unreactive (silver & gold)

Uses of Transition Metals

• Transition metals have many uses thanks to their properties:
  • Jewelry and electrical connectors
  • Electrical wires and printed circuits
  • Water pipes
  • Building materials (bridges, buildings, ships, cars)
  • Catalysts (chemical industry)
  • Coatings to prevent corrosion (e.g. chrome on car parts)

Polymer Chemistry

• Polymers are complex molecular compounds.
• Polymers are composed of numerous repeating units.
• Common sources of polymers include crude oil.
• Natural polymers come from living organisms.
• Synthetic polymers are created through lab reactions

Polymer Structure: Types

• Linear polymers: Repeat units link end-to-end; flexible; extensive van der Waals interactions possible
• Branched polymers: Branches occur from the main chains; lower density; less efficient packing
• Cross-linked polymers: linear chains cross-linked covalently; more rigid, less flexible
• Network polymers: chains highly cross-linked in a 3D network; more rigid and durable.

Polymer Chemistry: Properties

• Molecular weight: The weight of the polymer affects its properties. Higher molecular weights typically mean higher melting/softening temperature.
• Degree of Polymerization: The average number of repeat units in the chain, related to the number average molecular weight by a specific equation.

Copolymers

• Copolymers are polymers containing two types of repeat units.
• Copolymer types:
  • Alternating: alternating arrangement of different repeat units.
  • Random/Statical: randomly arranged repeat units.
  • Block: repeating blocks of the same repeat units.
  • Graft: branches containing repeating units attached to a homopolymer chain.

Polymer Crystallinity

• Crystalline polymers have an ordered atomic arrangement.
• Polymer crystallinity is the packing of molecular chains to form an ordered atomic array that can be determined via unit cells.

Thermoplastic and Thermosetting Polymers

• Thermoplastics: soften and liquefy upon heating, can be repeatedly melted & reshaped; characterized by a linear structure or branches that do not firmly bond together.
• Thermosets: form a rigid network that is not altered upon heating. They have extensive cross-links that make them durable, but can't be melted or reshaped.

Basic Concepts of Crystal Structures

• Crystal Structures: Atoms and ions form an ordered and repeating set of units to form crystalline solids.
• Unit Cells: The smallest repeating units in crystals. Various unit cell types exist; including simple cubic, body centered cubic, face centered cubic & hexagonal close packed cells.
• Density Computations: Density can be calculated by knowing the unit cell's number of associated atoms, its atomic weight, its volume and Avogadro's number.
• Types of Crystals: four basic categories - ionic, metallic, covalent & molecular.
• Amorphous Solids: Solids without a crystal lattice structures, like glass.