LECTURE 5.1LECTURE 5.1

LECTURE OUTLINELECTURE OUTLINE

Weekly Deadlines.Weekly Deadlines. Molecules, Monomers, Crystals Etc. (Part I)Molecules, Monomers, Crystals Etc. (Part I)

Name Structure 1: Introduction

Lectures Lecture 5.1 Molecules, Monomers, Crystals and Glasses ILecture 5.2 Molecules, Monomers, Crystals and Glasses II

Required Book Reading 1(For the end-of-UNIT quiz)

Part D:Prologue +Chapters 12 and 13

Animations Ian Harrison: "HistoryAtomF"BiographiesMineral of the Week

Assignments due this week Nothing this week.

Practice Quiz Practice quiz questions are available on ANGEL, in theLesson 05 folders.

End of Unit Quiz Quiz 5 will consist of twenty ~(20) questions for a total offifty (50) points. Quizzes are “individualized”, but with thequestions taken from a large database.

Material covered: Book Reading and Animations

MOLECULES,MONOMERS, MOLECULES,MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

(PART I)(PART I)

Definitions and Atomic ModelsDefinitions and Atomic Models

MOLECULES,MONOMERS, CRYSTALS MOLECULES,MONOMERS, CRYSTALS ETC.ETC.

The Hierarchical Levels of StructureThe Hierarchical Levels of StructureDefinition of a MoleculeDefinition of a MoleculeDefinition of a MonomerDefinition of a MonomerDefinition of a CrystalDefinition of a CrystalDefinition of a GlassDefinition of a GlassStudy QuestionsStudy Questions

DEFINITION OF A MOLECULEDEFINITION OF A MOLECULE

MoleculMolecule. e. A molecule is a stable, electrically A molecule is a stable, electrically neutral, discrete group of atoms, within which neutral, discrete group of atoms, within which the atoms are covalently bonded. Molecules the atoms are covalently bonded. Molecules should, at least potentially, be able to exist as should, at least potentially, be able to exist as separate entities in the gaseous state. separate entities in the gaseous state.

Molecular Material.Molecular Material. A substance may be A substance may be defined as molecular, if it comprises small, defined as molecular, if it comprises small, discrete groups of atoms, which are discrete groups of atoms, which are covalently bonded to each other, but to all covalently bonded to each other, but to all other atoms, by secondary bonds only.other atoms, by secondary bonds only.

EXAMPLES OF MOLECULESEXAMPLES OF MOLECULES

Figure 6. Ball and stick representation of several molecules, which are also monomers. a) A molecule/monomer ofphosphorous (P4). Both polymorphs of phosphorus (white and red) are comprised of P4 tetrahedra. b) The eight-membermonomer/molecule of sulfur. This monomer is the basic building block of both orthorhombic and monoclinic sulfur,and is also present in the liquid and gas phases. c) The tetrahedral monomer/molecule of methane.

MOLECULES,MONOMERS, CRYSTALS MOLECULES,MONOMERS, CRYSTALS ETC.ETC.

The molecule of water consists of one oxygen atom which The molecule of water consists of one oxygen atom which is covalently bonded to two oxygen atoms. The angle is covalently bonded to two oxygen atoms. The angle between the two bonds is about 105˚. The molecule and between the two bonds is about 105˚. The molecule and the monomer are one and the samethe monomer are one and the same

MOLECULES,MONOMERS, CRYSTALS MOLECULES,MONOMERS, CRYSTALS ETC.ETC.

A molecule of methane, A molecule of methane, consists of a single atom of consists of a single atom of carbon which is carbon which is tetrahedrallytetrahedrally bonded to four bonded to four hydrogen atoms. The hydrogen atoms. The molecule and monomer are molecule and monomer are equivalent.equivalent.

In general, carbon forms In general, carbon forms four bonds, and with a four bonds, and with a characteristic tetrahedral characteristic tetrahedral geometry. (A notable geometry. (A notable exception is graphite)exception is graphite)

DEFINITION OF A MONOMERDEFINITION OF A MONOMER

A monomer is the basic building block of any A monomer is the basic building block of any material. A small group, or assembly of atoms, material. A small group, or assembly of atoms, ions, etc., which is representative of the entire ions, etc., which is representative of the entire structure of the material.structure of the material.

The monomer must have the property that it can The monomer must have the property that it can create the entire material through the application create the entire material through the application of a simple set of rules, called a lattice or of a simple set of rules, called a lattice or translational form.translational form.

BUILDING A WALL;EGYPTIAN BUILDING A WALL;EGYPTIAN STYLESTYLE

TETRAHEDRAL MOMOMERSTETRAHEDRAL MOMOMERS

Ball and stick representations of two tetrahedral monomers. (b) and (c), both of which are created by decorating a geometric form (the tetrahedron of part a)) with atoms. a) A tetrahedral, geometric form. The centroid of the tetrahedron is indicated by the open circle. b) A monomer of the diamond form of carbon; a central carbon atom is tetrahedrally coordinated by four other carbon atoms. Note that the monomer of Figure 11b is not stable; each carbon atom needs to bond covalently to four other carbon atoms. c) A monomer of the silica-based (SiO2) materials. The central silicon atom is tetrahedrally coordinated by four oxygen atoms to yield a structural unit, that if ionically bonded, has the formula (SiO4)4-, i.e., it is not

electrically neutral.

THE FERRITIC FORM OF IRONTHE FERRITIC FORM OF IRON

THE SILICA MONOMERTHE SILICA MONOMER

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

The monomer of diamond The monomer of diamond consists of a single atom consists of a single atom of carbon, tetrahedrally of carbon, tetrahedrally bonded to four other bonded to four other carbon atoms.carbon atoms.

THE MONOMER IS NOT A THE MONOMER IS NOT A MOLECULE.MOLECULE.

Each carbon atom must Each carbon atom must bond to four other carbon bond to four other carbon atoms: the monomer is our atoms: the monomer is our notional building brick, and notional building brick, and it need not be stable!it need not be stable!

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

A “dimer” of diamond is A “dimer” of diamond is created when a second created when a second carbon atom is carbon atom is tetrahedrally tetrahedrally coordinated. The crystal coordinated. The crystal structure of diamond can structure of diamond can be built up by creating a be built up by creating a “trimer”, then a “trimer”, then a “tetramer”….“tetramer”….

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

The (SiOThe (SiO44) monomer which is ) monomer which is

characteristic of the various characteristic of the various polymorphs of silica (e.g., polymorphs of silica (e.g., quartz), silica glass and all quartz), silica glass and all the silicates.the silicates.

The central silicon atom is The central silicon atom is tetrahedrally bonded to four tetrahedrally bonded to four oxygen atomsoxygen atoms

This monomer is not a This monomer is not a molecule: it does not even molecule: it does not even have the correct have the correct composition!composition!

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

A “dimer” of e.g., quartz. Note that each silicon atom is bonded to four A “dimer” of e.g., quartz. Note that each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms. This oxygen atoms, and each oxygen atom is bonded to two silicon atoms. This yields the correct composition: SiOyields the correct composition: SiO22..

In crystalline materials which are based on the silica tetrahedron, the In crystalline materials which are based on the silica tetrahedron, the monomers are periodically arranged.monomers are periodically arranged.

In silica-based glasses, the monomers are arranged randomlyIn silica-based glasses, the monomers are arranged randomly

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

The monomer of polyethylene The monomer of polyethylene consists of two carbon atoms consists of two carbon atoms and four hydrogen atoms. The and four hydrogen atoms. The carbon atoms are tetrahedrally carbon atoms are tetrahedrally bonded to two carbon atoms bonded to two carbon atoms and two hydrogen atoms.and two hydrogen atoms.

The result of adding monomers The result of adding monomers to each other to produce a to each other to produce a dimer, a trimer, a tetramer…, is dimer, a trimer, a tetramer…, is a a macromolecule.macromolecule.

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

A small fragment of a macromolecule of polyethylene ( a “pentamer”). A A small fragment of a macromolecule of polyethylene ( a “pentamer”). A “real” macromolecule of PE might contain 10“real” macromolecule of PE might contain 1066 monomers. monomers.

Packing of these linear macromolecules can produce a crystalline polymer, Packing of these linear macromolecules can produce a crystalline polymer, called high-density polyethylene (HDPE).called high-density polyethylene (HDPE).

Note that for “polymers” the monomer is much smaller than the Note that for “polymers” the monomer is much smaller than the (macro)molecule.(macro)molecule.

THE MACROMOLECULE, AND THE THE MACROMOLECULE, AND THE MONOMER OF POLYETHYLENEMONOMER OF POLYETHYLENE

a) is a small segment of a macromolecule of polyethylenea) is a small segment of a macromolecule of polyethylene A typical macromolecule might contain 50,000 carbon atomsA typical macromolecule might contain 50,000 carbon atoms b) shows a monomer of polyethylene: it consists of two carbon atoms and b) shows a monomer of polyethylene: it consists of two carbon atoms and

four hydrogen atomsfour hydrogen atoms c) is a structural representation of the monomerc) is a structural representation of the monomer

aa

{ } { }CCHH

HH

a)

b) c)

MOLECULES, MONOMERS, MOLECULES, MONOMERS, CRYSTALS ETC.CRYSTALS ETC.

However, the macromolecules need not be straight, they may be curved, However, the macromolecules need not be straight, they may be curved, whilst still retaining the tetrahedral geometry of the monomers.whilst still retaining the tetrahedral geometry of the monomers.

It is now impossible to pack the macromolecules to create a crystalline It is now impossible to pack the macromolecules to create a crystalline polymer.polymer.

The amorphous low-density polyethylene (LDPE) resultsThe amorphous low-density polyethylene (LDPE) results