Characteristics, Classification, and Applications of Metals and Alloys

Metalanguage and Key Terminology

• Actinides: A series of fifteen metallic elements from actinium (atomic number $89$) to lawrencium (atomic number $103$) in the periodic table. They are all radioactive, with heavier members being extremely unstable and not naturally occurring.

• Alkali Metals: The metallic elements located in Group $1$ of the periodic table of elements.

• Alkaline Earth Metals: The metallic elements located in Group $2$ (Column $2\text{A}$) of the periodic table.

• Alloy: A mixture of a metal with at least one other element, usually another metal.

• Amalgam: An alloy composed of mercury and silver or tin, utilized for dental fillings due to its ability to be shaped when warm and its corrosion resistance.

• Brass: An alloy composed of copper and zinc that does not tarnish and is used in door knobs, buttons, and musical instruments.

• Corrosion: A natural process that converts a refined metal into a more chemically stable form such as an oxide, hydroxide, or sulfide; it represents the gradual destruction of materials by chemical and/or electrochemical reaction with their environment.

• Ductility: A measure of a material's ability to undergo significant plastic deformation before rupture, expressed as percent elongation or percent area reduction from a tensile test.

• Electrical Conductivity: The degree to which a specified material conducts electricity.

• Lanthanides: A group of $15$ chemical elements with atomic numbers $57$ through $71$, each possessing one valence electron in the $5\text{d}$ shell.

• Luster: A gentle sheen or soft glow, especially that of a partly reflective surface.

• Malleability: A physical property of metals defining the ability to be hammered, pressed, or rolled into thin sheets without breaking.

• Ore: A naturally occurring solid material from which a metal or valuable mineral can be profitably extracted.

• Reactivity: The ease and speed with which an element combines or reacts with other elements and compounds.

• Rusting: The specific term designated for the corrosion of iron, resulting from a chemical reaction between iron, oxygen, and water.

• Solder: An alloy of zinc and lead used in electronics to attach components to circuit boards.

• Sonority: A nonbinary phonological feature categorizing sounds into a relative scale.

• Steel: An alloy containing iron and other elements, such as carbon, nickel, and chromium.

• Thermal Conductivity: The rate at which heat passes through a specified material, expressed as the amount of heat that flows per unit time through a unit area with a temperature gradient of one degree per unit distance.

• Transition Metals: The chemical elements located in Groups $3$ through $12$ in the periodic table.

Essential Knowledge and Physical Properties of Metals

• Definition of Metals: A metal is a material that, when freshly prepared, polished, or fractured, exhibits a lustrous appearance and conducts electricity and heat relatively well. Metals are typically malleable (hammerable into thin sheets) or ductile (drawable into wires).

• Forms of Metals: Metals can exist as:

  • Elementary chemical substances (e.g., iron).

  • Alloys (e.g., stainless steel).

  • Molecular compounds (e.g., polymeric sulfur nitride).

• Abundance and Occurrence:

  • Approximately three-quarters ($75\%$) of all known chemical elements are metals.

  • Chemical elements comprising metals constitute $25\%$ of the Earth's crust.

  • The most abundant metals in the Earth's crust are aluminum, iron, calcium, sodium, potassium, and magnesium.

  • Most metals occur in ores (mineral-bearing substances). Unreactive metals such as copper, gold, platinum, and silver frequently occur in the free state.

• Atomic and Crystalline Structure:

  • Metals are usually crystalline solids characterized by simple crystal structures with close packing of atoms and high symmetry.

  • Atomic valence shells typically contain less than half of their full electron capacity (fewer than $4$ valence electrons).

  • Because of low outer shell electron counts, metal atoms tend not to form compounds with each other, but combine readily with nonmetals (e.g., oxygen, sulfur), which contain more than half their maximum valence electrons.

• Physical Properties:

  • Luster: Possess a reflective surface glow.

  • Malleability: Can be pressed or rolled without fracture (e.g., copper formed into flat sheets).

  • Ductility: Can be pulled into thin wiring (e.g., copper wire).

  • Conductivity: High efficiency in thermal and electrical transfer.

  • Magnetism: Selected metals—iron ($\mathbf{Fe}$), cobalt ($\mathbf{Co}$), and nickel ($\mathbf{Ni}$)—are attracted to magnets and can be magnetized.

  • State at Room Temperature: Almost all metals are solid at room temperature, with the exception of mercury ($\mathbf{Hg}$), which is a liquid.

Chemical Properties, Corrosion, and Oxidation

• Reactivity Mechanism: Metals generally react by losing valence electrons to other atoms.

• Variations in Reactivity:

  • High Reactivity: Sodium ($\mathbf{Na}$) reacts vigorously upon exposure to air or water and must be stored submerged under oil in sealed containers.

  • Low Reactivity / Noble Metals: Gold ($\mathbf{Au}$) and platinum ($\mathbf{Pt}$) are prized for their extreme chemical unreactivity and rarity. Gold objects can endure underwater or buried for thousands of years without degradation.

  • Intermediate Reactivity: Iron ($\mathbf{Fe}$) reacts slowly with atmospheric oxygen to form iron oxide.

• Corrosion Process:

  • Defined as the gradual destruction and weakening of a metal caused by chemical reactions with atmospheric elements. Corrosion alters appearance, reduces mechanical strength, and destroys structural integrity.

  • Protection against corrosion is achieved by applying surface coatings such as paint or protective chemical sealants.

• Aluminum Anti-Corrosion Mechanism:

  • Although aluminum is highly reactive chemically, it resists continuous atmospheric corrosion.

  • Atmospheric oxygen reacts with surface aluminum atoms to form a dense, micro-thin layer of aluminum oxide.

  • This oxide layer adheres firmly to the metal surface, creating an impermeable barrier against further oxidation.

• Rusting of Iron:

  • Rusting is the specific chemical corrosion process affecting iron.

  • Requires the concurrent presence of iron, oxygen, and water:     $\text{iron} + \text{oxygen} + \text{water} \rightarrow \text{hydrated iron oxide}$

  • Chemical compound produced: hydrated iron oxide.

  • Rate acceleration: Exposure to salt significantly increases the rate of rusting, rapidly degrading seaside structures and vehicles.

Classification of Metals in the Periodic Table

• Reactivity Trend: Reactivity of metals systematically decreases moving from left to right across the periodic table.

• Group 1: Alkali Metals:

  • Elements: Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium.

  • Outer shell configuration: Single valence electron ($1\text{e}^-$).

  • Properties: Exceptionally soft (can be sliced with a knife), low density, low melting and boiling points relative to other metals. Retain high thermal/electrical conductivity, malleability, and ductility.

• Group 2 (Column 2A): Alkaline Earth Metals:

  • Elements: Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium.

  • Outer shell configuration: Two valence electrons ($2\text{e}^-$).

  • Properties: Shiny and silvery appearance in pure elemental form.

• Groups 3–12: Transition Metals:

  • Defined by atoms with incomplete $\text{d}$ sub-shells ($\text{d}$-block elements).

  • Electron removal occurs primarily from outer $\text{d}$ orbitals following initial loss from outer $\text{s}$ orbitals.

  • Characteristics:

  • Formation of compounds in multiple oxidation states.

  • Formation of paramagnetic compounds due to unpaired $\text{d}$ electrons.

  • Highly conductive, malleable, ductile, and lustrous with a silver-white color (exception: copper exhibits a brownish-red color).

  • Similar atomic sizes allow atoms to substitute for one another in crystal lattices, readily forming alloys.

  • Occur primarily as compounds in the Earth's crust rather than pure substances.

  • Metal extraction techniques include pyrometallurgical (high-temperature processing) and hydrometallurgical (aqueous solution extraction) methods.

• Lanthanides:

  • Set of $15$ elements with atomic numbers $57$ through $71$ located below the main periodic table grid.

  • Possess one valence electron in the $5\text{d}$ shell.

  • Properties: Soft, malleable, shiny, highly conductive.

  • Naturally co-occur in minerals and are difficult to isolate due to nearly identical chemical behavior. Frequently alloyed with common metals.

• Actinides:

  • Set of $15$ elements with atomic numbers $89$ through $103$ (Actinium to Lawrencium).

  • Named after the first element in the series, Actinium.

  • All members are radioactive; heavier members are synthetic and extremely unstable. Naturally occurring actinides are limited to trace amounts of Uranium and Thorium.

  • Heavy radioactive isotopes (e.g., Plutonium, Thorium, Uranium) are used in nuclear reactors and weapons.

  • Discovery of Transuranium Elements:

  • Scientific belief once held Uranium (atomic number $92$) as the ultimate chemical boundary.

  • University of California physicists Edwin McMillan ($1907\text{--}1991$) and Philip Abelson ($1913\text{--}2004$) investigated nuclear fission (splitting of an atomic nucleus releasing huge energy).

  • Their work led to the discovery of transuranium elements beyond atomic number $92$:

    • Neptunium (named after Neptune).

    • Plutonium (atomic number $94$, named after Pluto).

    • Americium (atomic number $95$, discovered $1944$).

    • Curium (atomic number $96$, discovered $1944$).

    • Berkelium (atomic number $97$, discovered $1949$).

    • Californium (atomic number $98$, discovered $1950$).

    • Einsteinium (atomic number $99$, discovered $1952$).

    • Fermium (atomic number $100$, discovered $1952$).

    • Mendelevium (atomic number $101$, discovered $1955$).

    • Nobelium (atomic number $102$, discovered $1958$).

    • Lawrencium (atomic number $103$, discovered $1961$).

• Metalloids (Semi-metals):

  • Commonly recognized elements: Boron, Silicon, Germanium, Arsenic, Antimony, and Tellurium (uncommon additions: Polonium and Astatine).

  • Exhibit intermediate properties: behave as non-metals when reacting with metals, and as metals when reacting with non-metals.

  • Form amphoteric oxides and function as semiconductors.

• Other Metals (Post-Transition Metals):

  • Positioned to the right of the transition metals on the periodic table.

  • Properties: Strong, ductile, malleable, highly heat and electrically conductive, opaque, with relatively high physical density.

Alloys, Composition, and Engineering Applications

• Definition and Atomic Mechanism:

  • An alloy is a mixture of a metal with at least one other chemical element.

  • In pure metals (e.g., pure iron), identical atoms arrange in densely packed layers that slide across one another easily under stress, making pure metals relatively soft.

  • Adding foreign atoms of differing sizes distorts the regular crystalline lattice. This distortion prevents layers from sliding smoothly, substantially increasing mechanical strength and hardness.

  • Material scientists adjust constituent ratios to tailor specific alloy properties.

• Historical and Common Alloys:

  • Bronze: Copper and tin alloy, used extensively prior to the development of iron extraction techniques.

  • Brass: Copper and zinc alloy. Non-tarnishing; used in door knobs, buttons, and musical instruments.

  • Solder: Zinc and lead alloy. Used in electronics for securing components to printed circuit boards.

  • Amalgam: Mercury mixed with silver or tin. Formable when warm and highly corrosion-resistant; used for dental fillings.

• Gold Alloys:

  • Pure gold ($24\text{k}$) is soft and malleable.

  • Jewelry requires alloying to enhance hardness and modify color:

  • Yellow Gold: Alloy of gold, copper, and silver (higher copper proportions yield redder/rose shades).

  • White Gold: Alloy of gold with nickel, platinum, or palladium. Approximately $12\%$ of people exhibit nickel allergies.

• Coinage Alloys:

  • Traditional coins were minted from pure copper. As copper commodity values rose, raw metal content surpassed face value.

  • Since $1992$, UK copper coins have been produced using copper-plated steel, making them magnetic and easily separable by age using magnets.

• Steel Classifications and Types:

  • Steel is an iron alloy containing carbon and additional elements (e.g., nickel, chromium). Stronger than pure iron, used in products ranging from cookware to suspension bridges.

• Carbon content ranges up to $2\%$:

  • Low Carbon Steel: Contains less than $0.25\%$ carbon.

  • High Carbon Steel: Contains more than $0.5\%$ carbon (increases hardness).

  • Stainless Steel: Iron alloy containing at least $11\%$ chromium, along with smaller quantities of nickel and carbon. Chromium imparts corrosion resistance.

  • Titanium Steel: Iron alloyed with titanium.

Smart Alloys

• Smart Materials: Materials capable of altering one or more physical characteristics in response to external environmental stimuli.

• Shape Memory Alloys (SMA): Metals that can be deformed and subsequently return to their original pre-deformed shape upon application of an appropriate stimulus.

• Nitinol:

  • A shape memory alloy composed of nickel and titanium.

  • Applications:

  • Eyeglass frames that retain shape memory and resist breakage when crushed.

  • Medical orthopedic devices used to hold severely fractured bones in alignment during healing.

Questions and Review Concepts

• Check Questions:

  1. What is stainless steel?

  2. What are the most common metals used in construction?

  3. What is the difference between Iron and Steel?

  4. Why isn't steel termed as a metal?

• Analysis Questions:

  1. Differentiate metals from non-metals based on physical and chemical properties.

  2. What makes stainless steel stainless? Explain the protective role of chromium.

  3. Which is stronger, Steel or Titanium? Explain.

  4. What are the 4 types of steel?

• Summary Task:

  • Construct a vis-à-vis comparison of different alloyed materials, detailing their individual advantages, disadvantages, and best applications.