A1 Material Science Introduction

Option A SummaryMaterialsA1 Material science introductionUnderstandings Materials are classified based on their uses, properties, or bonding and structure. The properties of a material based on the degree of covalent, ionic, or metallic character in a compound can be deduced from its position on a bonding triangle. Composites are mixtures in which materials are composed of two distinct phases, a reinforcing phase that is embedded in a matrix phase.Guidance Consider properties of metals, polymers and ceramics in terms of metallic, covalent and ionic bonding. See section 29 of the data booklet for a triangular bonding diagram.Applications Use of bond triangle diagrams for binary compounds from electronegativity data. Evaluation of various ways of classifying materials. Relating physical characteristics (melting point, permeability, conductivity, elasticity, brittleness) of a material to its bonding and structures (packing arrangements, electron mobility, ability of atoms to slide relative to one another).Guidance Permeability to moisture should be considered with respect to bonding and simple packing arrangements.

Materials and properties Metals are strong and malleable Glasses are transparent and brittle Ceramics are excellent insulators except superconductors Substances can be classified as ionic, covalent or metallic but some show intermediate properties and this is determined by the difference in electronegativity of elements

Materials and propertiesSince CsF is the most ionic compound with difference in electronegativity = 3.2, the ionic character of a compound can be defined relative to this value:

Percentage ionic character = x 100%Classes of materialThere are four distinct classes of materials: metals, polymers, ceramics and composites1. Ceramic All solid materials (except metals and their alloys) are ceramics, glasses and semiconductors are also considered as ceramics sometimes Made by high-temperature processing of inorganic raw materials Have properties opposite to those of metals Forms giant ionic or giant covalent structures and thus are very hard yet brittle (because of ions) Can be porous as they are gaps in their structure that allows water molecule to passExample: Glass is formed when molten silicon dioxide and ionic metal oxides are mixed and cooled quickly so that the solid formed retains some disorder of the liquid2. Composite Composites are formed when strong and hard fiber material are embedded in a matrix of another material Fibers confer strength while matrix confers toughness, these properties of a composite can be changed or tailor-made by adjusting the amount or orientation of the fibersExamples

3. Metal Metal cationic lattice bathing in a sea of delocalized electrons Malleable and ductile because layers of atoms can slide easily relative to one another Excellent heat and electrical conductivity because of the delocalized sea of electrons Transition metals are harder and have higher melting points than main group metals due to the involvement of both s and d electrons in metallic bonding Usually too soft in pure form, becomes tougher when alloyed with other elementsExample: Gold is very soft in its pure form; it can be alloyed with copper to make rings, which are more wear-resistant4. Polymer Polymer is a macromolecular structure consist of many monomer units joined either by addition of condensation polymerization Although polymer is a molecule, the extremely large size of it means threads of polymer are held together by very strong London dispersion force or van der Waals force and so they are solids A very important example of polymer is plastic in which individual polymer thread may (thermosetting plastics) or may not (thermoplastics) cross-link Thermoplastics tend to be elastic as separated chains can re-bond by LDF after stress is removed while thermosetting plastics tend to be hard and brittle because of cross-linksA2 Metals and inductively coupled plasma (ICP) spectroscopyUnderstandings Reduction by coke (carbon), a more reactive metal, or electrolysis are means of obtaining metals from their ores. The relationship between charge and the number of moles of electrons is given by Faradays constant, F. Alloys are homogeneous mixtures of metals with other metals or non-metals. Diamagnetic and paramagnetic compounds differ in electron spin pairing and their behavior in magnetic fields. Trace amounts of metals can be identified and quantified by ionizing them with argon gas plasma in inductively coupled plasma (ICP) spectroscopy using mass spectroscopy ICP-MS and optical emission spectroscopy ICP-OES.Guidance Faradays constant is given in the IB data booklet in section 2. Details of operating parts of ICP-MS and ICP-OES instruments will not be assessed.Applications Deduction of redox equations for the reduction of metals. Relating the method of extraction to the position of a metal on the activity series. Explanation of the production of aluminium by the electrolysis of alumina in molten cryolite. Explanation of how alloying alters properties of metals. Solving stoichiometric problems using Faradays constant based on mass deposits in electrolysis. Discussion of paramagnetism and diamagnetism in relation to electron structure of metals. Explanation of the plasma state and its production in ICP-MS and ICP-OES. Identify metals and abundances from simple data and calibration curves provided from ICP-MS and ICP-OES. Explanation of the separation and quantification of metallic ions by MS and OES. Uses of ICP-MS and ICP-OES.Guidance Only analysis of metals should be covered. The importance of calibration should be covered.

Metal extraction and reactivity Reactive metals are found in ores while unreactive metals exist in native form in nature Ores are usually metal oxides, sulphides or carbonates mixed with impurities like sand Steps of extraction:Purification of ore Reduction Different methods of extraction may be used, depending on the reactivity of the metal, e.g. electrolysis or reduction by coke or carbon monoxide

Prepared by Toman Lam