LECTURE 5.1

LECTURE OUTLINE Weekly Deadlines Weekly Deadlines Molecules, Monomers, Crystals, Etc. (Part I) Molecules, Monomers, Crystals, Etc. (Part I) Lesson 5 Prototype Quiz Lesson 5 Prototype Quiz

MOLECULES, MONOMERS, CRYSTALS, ETC. (PART I) Definitions and Atomic Models

MOLECULES, MONOMERS, CRYSTALS, ETC. The Hierarchical Levels of Structure The Hierarchical Levels of Structure Definition of a Molecule Definition of a Molecule Definition of a Monomer Definition of a Monomer Definition of a Crystal Definition of a Crystal Definition of a Glass Definition of a Glass Molecular or Not? Molecular or Not? Matter and Form Matter and Form

DEFINITION OF A MOLECULE Molecule. A molecule is a stable, electrically neutral, discrete group of atoms within which the atoms are covalently bonded. Molecules should, at least potentially, be able to exist as separate entities in the gaseous state. Molecule. A molecule is a stable, electrically neutral, discrete group of atoms within which the atoms are covalently bonded. Molecules should, at least potentially, be able to exist as separate entities in the gaseous state. Molecular Material. A substance may be defined as molecular if it comprises small, discrete groups of atoms which are covalently bonded to each other but are joined by only secondary bonds to all other atoms. Molecular Material. A substance may be defined as molecular if it comprises small, discrete groups of atoms which are covalently bonded to each other but are joined by only secondary bonds to all other atoms.

MOLECULES, MONOMERS, CRYSTALS, ETC. The molecule of water consists of one oxygen atom which is covalently bonded to two hydrogen atoms. The angle between the two bonds is about 105˚. The molecule and the monomer are one and the same. The molecule of water consists of one oxygen atom which is covalently bonded to two hydrogen atoms. The angle between the two bonds is about 105˚. The molecule and the monomer are one and the same.

MOLECULES, MONOMERS, CRYSTALS, ETC. A molecule of methane consists of a single atom of carbon which is tetrahedrally bonded to four hydrogen atoms. The molecule and monomer are equivalent. A molecule of methane consists of a single atom of carbon which is tetrahedrally bonded to four hydrogen atoms. The molecule and monomer are equivalent. In general, carbon forms four bonds with a characteristic tetrahedral geometry. (A notable exception is graphite.) In general, carbon forms four bonds with a characteristic tetrahedral geometry. (A notable exception is graphite.)

DEFINITION OF A MONOMER A monomer is the basic building block of any material. It is a small group or assembly of atoms, ions, etc., which is representative of the entire structure of the material. A monomer is the basic building block of any material. It is a small group or assembly of atoms, ions, etc., which is representative of the entire structure of the material. A key property of a monomer is that it can create the entire material through the application of a simple set of rules, called a lattice or translational form. A key property of a monomer is that it can create the entire material through the application of a simple set of rules, called a lattice or translational form.

MOLECULES, MONOMERS, CRYSTALS, ETC. The monomer of diamond consists of a single atom of carbon tetrahedrally bonded to four other carbon atoms. The monomer of diamond consists of a single atom of carbon tetrahedrally bonded to four other carbon atoms. THE MONOMER IS NOT A MOLECULE. THE MONOMER IS NOT A MOLECULE. Each carbon atom must bond to four other carbon atoms. The monomer is our notional building brick, and it need not be stable! Each carbon atom must bond to four other carbon atoms. The monomer is our notional building brick, and it need not be stable!

MOLECULES, MONOMERS, CRYSTALS, ETC. A “dimer” of diamond is created when a second carbon atom is tetrahedrally coordinated. The crystal structure of diamond can be built up by creating a “trimer,” then a “tetramer,” and so on. A “dimer” of diamond is created when a second carbon atom is tetrahedrally coordinated. The crystal structure of diamond can be built up by creating a “trimer,” then a “tetramer,” and so on.

MOLECULES, MONOMERS, CRYSTALS, ETC. The (SiO 4 ) monomer is characteristic of the various polymorphs of silica (e.g., quartz), silica glass, and all the silicates. The (SiO 4 ) monomer is characteristic of the various polymorphs of silica (e.g., quartz), silica glass, and all the silicates. The central silicon atom is tetrahedrally bonded to four oxygen atoms. The central silicon atom is tetrahedrally bonded to four oxygen atoms. This monomer is not a molecule—it does not even have the correct composition! This monomer is not a molecule—it does not even have the correct composition!

MOLECULES, MONOMERS, CRYSTALS, ETC. A “dimer” of quartz, for example. Note that each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms. This yields the correct composition: SiO 2. A “dimer” of quartz, for example. Note that each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms. This yields the correct composition: SiO 2. In crystalline materials that are based on the silica tetrahedron, the monomers are periodically arranged. In crystalline materials that are based on the silica tetrahedron, the monomers are periodically arranged. In silica-based glasses, the monomers are arranged randomly. In silica-based glasses, the monomers are arranged randomly.

MOLECULES, MONOMERS, CRYSTALS, ETC. The monomer of polyethylene consists of two carbon atoms and four hydrogen atoms. The carbon atoms are tetrahedrally bonded to two carbon atoms and two hydrogen atoms. The monomer of polyethylene consists of two carbon atoms and four hydrogen atoms. The carbon atoms are tetrahedrally bonded to two carbon atoms and two hydrogen atoms. The result of adding monomers to each other to produce a dimer, a trimer, a tetramer, etc., is a macromolecule. The result of adding monomers to each other to produce a dimer, a trimer, a tetramer, etc., is a macromolecule.

MOLECULES, MONOMERS, CRYSTALS, ETC. A small fragment of a macromolecule of polyethylene ( a “pentamer”). A real macromolecule of PE might contain 10 6 monomers. A small fragment of a macromolecule of polyethylene ( a “pentamer”). A real macromolecule of PE might contain 10 6 monomers. Packing of these linear macromolecules can produce a crystalline polymer, called high-density polyethylene (HDPE). Packing of these linear macromolecules can produce a crystalline polymer, called high-density polyethylene (HDPE). Note that for polymers the monomer is much smaller than the (macro)molecule. Note that for polymers the monomer is much smaller than the (macro)molecule.

THE MACROMOLECULE AND THE MONOMER OF POLYETHYLENE Figure 1a is a small segment of a macromolecule of polyethylene. Figure 1a is a small segment of a macromolecule of polyethylene. A typical macromolecule might contain 50,000 carbon atoms. A typical macromolecule might contain 50,000 carbon atoms. Figure 1b shows a monomer of polyethylene. It consists of two carbon atoms and four hydrogen atoms. Figure 1b shows a monomer of polyethylene. It consists of two carbon atoms and four hydrogen atoms. Figure 1c is a structural representation of the monomer. Figure 1c is a structural representation of the monomer.

MOLECULES, MONOMERS, CRYSTALS, ETC. However, the macromolecules need not be straight. They may be curved while still retaining the tetrahedral geometry of the monomers. However, the macromolecules need not be straight. They may be curved while still retaining the tetrahedral geometry of the monomers. It is now impossible to pack the macromolecules to create a crystalline polymer. It is now impossible to pack the macromolecules to create a crystalline polymer. The result is amorphous low-density polyethylene (LDPE). The result is amorphous low-density polyethylene (LDPE).