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14.16: Chemistry

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    45598
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    This is a small discussion of chemistry, for a true engineering for chemistry course go to the Chemistry for Engineers course for Prince Georges Community College (PGCC):

    https://chem.libretexts.org/Courses/Prince_Georges_Community_College/Chemistry_2000%3A_Chemistry_for_Engineers_(Sinex)

    The course above represents an atoms first approach which basically starting at the most fundamental particle and moving up to molecules and structures. For this brief introduction we will only focus on the basic atom first introduction and crystal structures alone.

    Particles form other particles form other particles

    The most basic particles are the elementary particles. These particles consist of quarks, electrons, and other particles. With the exception of the electron these particles really don't play a role in most of chemistry (except nuclear chemistry). Quarks make protons (two up quarks and one down quark) and neutrons (two down quarks and one up quark).

    Periodic table of elementary particles including quarks, electron, muon, neutrino, photon, and higgs.
    This is a table of the most common elementary particles and can be found on Wikipedia on the subject of the Elementary Particles. Credit: MissMJ, Cush - Own work by uploader, PBS NOVA [1], Fermilab, Office of Science, United States Department of Energy, Particle Data Group

    Atoms

    Atoms consist of protons, neutrons, and electrons with the protons (and neutrons) making up the nucleus which is surrounded by "orbiting" electron. There are less than 100 unique stable atoms which we call elemental atoms. The bulk of the mass of an atom is in the nucleus, but the volume is the inner portion of the "electron cloud." Electrons give rise to most of the electrical, mechanical, chemical, and thermal properties, or more precisely the orbital shells (or better yet cloud) determine the properties. Elements form bonds to other elements to form molecules.

    Periodic Tables

    All atoms in nature and that are relevant to chemistry were created by astronomical events.

    Periodic table of elements and their associated astronomical origin.
    Periodic table that explains the origins of the various elements (in nature only) through astronomical events. Note the elements with a color not in the legend are elements that are not natural but created by humankind. Credit: Wikipedia: Cmgless. CC BY-SA 3.0

    For a more traditional periodic table we have atomic weights and ionization energies among other useful information.

    Modern periodic table form NIST.
    Modern-day traditional periodic table from NIST. This has the artificially created elements which will not have any useful application in engineering. Credit: Alexander Kramida, Karen Olsen, and Yuri Ralchenko, NIST, Physical Measurement Laboratory

    Molecules and Crystals

    Atoms bond to other atoms with different bonding methods with the most common being ionic and covalent bonds. When atoms bond together in a stable structure that is a molecule. Gases, liquids, and solids are three of the most common phases of matter. Gases, liquids, and solids consist of numerous atoms or molecules or compounds. Gases and liquids have some applications in engineering, but primarily solids dominate the field. For this brief topic page, gases and liquids will not be discussed but rather saved for Chemistry. Solids can take different forms some of which are amorphous and some of which are crystalline. Crystals can be formed from elements or from molecules. For instance salt (NaCl) is formed by elements but not molecules whereas white phosphorus is formed from molecules (other allotropes of phosphorus are not considered molecular crystals but macromolecules or amorphous polymers1). In general engineers refer to solids as materials as in solid materials (civil and mechanical engineering) and materials science (most disciplines of engineering).

    Materials

    There are three main type of materials: metallic materials, polymeric materials, and ceramic materials. Metals are crystals, polymers can be crystalline but are in general considered not crystals, and ceramics are a mix of metallic and non-metallic materials. Metals are ductile and strong (not brittle) and are also electrically and thermally conductive. Polymers are less easily characterized because ot the many different types of polymers. DNA, RNA, and proteins are polymers. Wood is a polymeric material that is used in engineering. Ceramics have a high degree of hardness and temperature resistance, are light weight, but are brittle and porous. Detailed discussions of polymers and ceramics will wait until after completion of chemistry for engineers.

    Crystals are solids that have a repeated structure defined by seven different lattice systems2 that have fourteen different "unit cells" which we call Bravais lattices. Most elemental metals are either body-centered cubic (BCC), face-center cubic (FCC), or hexagonal closed-back (HCP) because these structures are densely packed and, therefore, have lower energy and are more stable. Iron has a unit cell of BCC with a length of 0.287 nanometers at room temperature which is quite small. The lattice structure of a metal helps determine a number of properties of metals (ductility, electric properties, etc.). For instance, the Fourier transform of the Bravais lattice (which are Bravais lattices themselves) is a reciprocal lattice that is helps define bandgaps (determines where we have a conductor, insulator, or semiconductor) in materials.

    Image of the 14 Bravais lattices that define basic crystal structures.
    Models of the fourteen possible basic crystal structures of solid elements. This consists of seven lattice systems that make up the fourteen Bravais lattices shown here. Most metals have either an FCC, BCC, or SC crystal structure.

    Manipulatives

    Below are two demonstration projects3 from Wolfram (Mathematica) allowing you to manipulate (rotate and change): 1) the seven lattice systems (not crystal systems) and 2) the SC, FCC, BCC, and diamond (two FCCs merged) lattice structures for additional information. The demonstration projects at Wolfram have interesting examples of physics, chemistry, engineering, and other subjects that you might want to investigate on your own.

    This concludes this discussion on chemistry with a dose of materials science which is very important to all disciplines of engineering (for example, materials for building structures like dwellings, laboratories, mining equipment, cars, pencils, and musical instruments, and materials for electronics and electrical devices). All students are advised to take chemistry for engineers and scientists and materials science for engineers and scientists for a complete engineering education.


    1Polymers have a range of types from crystalline polymers to amorphous polymers. Something that is polymer-like but not consisting of monomers is considered a macromolecule (not a polymer, crystalline, or ceramic), though there is some semantics debate on this. This subject would be explored in Materials Science for Engineers and Scientists.

    2Crystal systems (geology) are not lattice system though they are very similar. Sometimes they are confused however there is an easy way to tell if lattice system should be used instead of crystal system. If one of the structures is rhombohedral (which is a trigonal crystal system) then we have a lattice system.

    3Click on the menu symbol next to "Created with Wolfram Technology" to get general information. The attribution to the two demonstrations shown, respectively, are S. M. Blinder, "The Seven Crystal Classes", http://demonstrations.wolfram.com/TheSevenCrystalClasses/, Wolfram Demonstrations Project, Published: March 7 2011 and Bianca Eifert, "Cubic Crystal Lattices", http://demonstrations.wolfram.com/CubicCrystalLattices/, Wolfram Demonstrations Project, Published: March 7 2011


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