LECTURE 7.1LECTURE 7.1

LECTURE OUTLINELECTURE OUTLINE

Weekly Deadlines.Weekly Deadlines.• The Metallic BondThe Metallic Bond The van der Waals BondThe van der Waals Bond The Hydrogen BondThe Hydrogen Bond

Name Structure 3: Bonding, Crystal Structures and Properties

Lectures Lecture 7.1 Metallic, van der Waals and Hydrogen BondingLecture 7.2 Bonding in Polymers

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

Part D:Chapters 17, 18, 19 and 20

Animations Ian Harrison: "PolymerSynthF" “StateMatterF”BiographiesMineral of the Week

Assignments due this week Nothing

Practice Quiz Practice quiz questions are available on ANGEL, in theLesson 07 folders.

End of Unit Quiz Quiz 7 will consist of ~ thirty (30) questions for a total ofseventy (70) points. Quizzes are “individualized”, but withthe questions taken from a large database.

Material covered: Book Reading and Animations

THE METALLIC BONDTHE METALLIC BOND

The bonds formed between an array of positively The bonds formed between an array of positively charged metallic cations and a "sea" of charged metallic cations and a "sea" of negatively charged, free-electrons, the latter negatively charged, free-electrons, the latter being "donated" from the outer shells of the being "donated" from the outer shells of the constituent atoms. constituent atoms.

Metallic bonds are Metallic bonds are non-directional.non-directional. Occurs for all metallic elements and their alloys Occurs for all metallic elements and their alloys

(i.e., Group I, I and III metals and for the (i.e., Group I, I and III metals and for the transition metals), to form close-packed solidstransition metals), to form close-packed solids

METALLIC BONDMETALLIC BOND

Metallic Bond: arises from the electrostatic attraction between cation cores and an electron cloud. The electrons are said to be delocalized, because they are not confined, to any cation core, but are “free” to move between the cation cores.Hence, the metallic bond is non-directional.

a

+ +_

METALLIC BONDINGMETALLIC BONDING

CUBIC CLOSE PACKING ICUBIC CLOSE PACKING I

CUBIC CLOSE PACKING IICUBIC CLOSE PACKING II

CUBIC CLOSE PACKING IIICUBIC CLOSE PACKING III

BODY CENTERED CUBICBODY CENTERED CUBIC

THE THREE COMMON THE THREE COMMON METALLIC CRYSTAL METALLIC CRYSTAL

STRUCTURESSTRUCTURES

VAN DER WAALS BONDVAN DER WAALS BOND

Weak, secondary bonds formed by Weak, secondary bonds formed by the attraction of the attraction of fluctuating dipolesfluctuating dipoles between e.g., atoms of the noble between e.g., atoms of the noble gases, and between molecules. van gases, and between molecules. van der Waals bonds are der Waals bonds are non-directionalnon-directional..

THE VAN DER WAALS BONDTHE VAN DER WAALS BOND

THE VAN DER WAALS BOND THE VAN DER WAALS BOND AND POLYETHYLENEAND POLYETHYLENE

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CCCCCCCCHHHHHHHHHHHHHHHHSingle Polyethylene ChainPolymer Chains

a) b){} Intermolecular Intramolecular

HYDROGEN BONDHYDROGEN BOND

Weak, secondary bonds formed by Weak, secondary bonds formed by the attraction of the attraction of polar moleculespolar molecules. A . A polar molecule (or dipole) results polar molecule (or dipole) results from a permanent imbalance in the from a permanent imbalance in the electron distribution in a molecule, electron distribution in a molecule, between an electronegative atom between an electronegative atom (e.g., oxygen) and an electropositive (e.g., oxygen) and an electropositive atom (e.g., hydrogen). Hydrogen atom (e.g., hydrogen). Hydrogen bonds are bonds are directionaldirectional..

THE COVALENT BOND AND THE COVALENT BOND AND WATERWATER

The water molecule consists of one oxygen atom, covalently The water molecule consists of one oxygen atom, covalently bonded to two hydrogen atoms.bonded to two hydrogen atoms.

However, the oxygen atom attracts the shared electron pairs more However, the oxygen atom attracts the shared electron pairs more strongly than do the hydrogen atoms, and the shared electrons strongly than do the hydrogen atoms, and the shared electrons “spend more time” with the oxygen atom. Hence, a permanent “spend more time” with the oxygen atom. Hence, a permanent dipole develops, with slightly positive charges on the hydrogen dipole develops, with slightly positive charges on the hydrogen atoms, and slightly negative charges on the oxygen atoms.atoms, and slightly negative charges on the oxygen atoms.

THE HYDROGEN BOND, AND THE THE HYDROGEN BOND, AND THE CRYSTAL STRUCTURE OF ICECRYSTAL STRUCTURE OF ICE

The monomer of the ice structure consists of a central, The monomer of the ice structure consists of a central, covalently bonded molecule of water, which is hydrogen covalently bonded molecule of water, which is hydrogen bonded to four other water molecules.bonded to four other water molecules.

When the monomers are assembled to create the crystal When the monomers are assembled to create the crystal structure of ice, a hexagonal material results.structure of ice, a hexagonal material results.

MAKING SNOWBALLSMAKING SNOWBALLS

aa

“Original” surfaceliquid layer is now“internal”“Internal” liquid watersolidifies and sintersthe particles togetherIce CrystalLiquid WaterSurface Layera) b) c)Modest hand-pressure bringsisolated ice grains into contactOriginalIce Crystal

THE “SURFACE” STRUCTURE THE “SURFACE” STRUCTURE OF ICEOF ICE

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Surface Layer(A Fraction of Missing Bonds)Ice (Solid)Liquid Surface Layer(Due to Missing Bonds)VaporWATERMOLECULE~-10˚Cb)Ice (Solid)

VaporWATERMOLECULEWell below ˚Ca)

THE SPECIFIC THE SPECIFIC GRAVITY/VOLUME OF WATERGRAVITY/VOLUME OF WATER

THE ANOMOLOUS COOLING THE ANOMOLOUS COOLING BEHAVIOR OF WATERBEHAVIOR OF WATER

THE SPECIFIC VOLUME OF THE SPECIFIC VOLUME OF WATERWATER

HYDROGEN BONDING AND THE HYDROGEN BONDING AND THE MELTING/BOILING POINTS OF WATERMELTING/BOILING POINTS OF WATER

HYDROGEN BONDING AND THE HYDROGEN BONDING AND THE MELTING/BOILING POINTS OF WATERMELTING/BOILING POINTS OF WATER

A COPMPARISON OF ICE WITH A COPMPARISON OF ICE WITH OTHER “OXIDES”OTHER “OXIDES”