Bonding in SolidsBonding in Solids

Valentin PanyushenkoValentin PanyushenkoChris ZhengChris Zheng

Molecular SolidsMolecular Solids

Held together by Held together by intermolecular forcesintermolecular forces

Forces are weak; solidForces are weak; solidsoft; low melting pointssoft; low melting points

Typically gas or liquid inTypically gas or liquid inroom temperatureroom temperature

Ex. Ar, HEx. Ar, H22O, COO, CO22

Molecular SolidsMolecular Solids

Property of molecular solids depend on:Property of molecular solids depend on: Strength of the forcesStrength of the forces Abilities of molecules to pack efficiently in 3DAbilities of molecules to pack efficiently in 3D

CH3 OH

Benzene Toluene PhenolMelting point (˚C) 5 -95 43Boiling point (˚C) 80 111 182

Intermolecular ForcesIntermolecular Forces London dispersion: weakest;London dispersion: weakest;

result from attractions betweenresult from attractions betweendipolesdipoles

H Bonding: strongest; molecules H Bonding: strongest; molecules containing H bond to an electro-containing H bond to an electro-negative elementnegative element

Dipole-dipole: attraction between Dipole-dipole: attraction between the + end of one molecule and the + end of one molecule and the – end of anotherthe – end of another

Covalent-Network SolidsCovalent-Network Solids

Held together by covalent Held together by covalent bondsbonds

Compared to molecular Compared to molecular solids: harder and higher solids: harder and higher melting points melting points

In diamond:In diamond: Each C is bonded to four Each C is bonded to four

other Cother CMelting point: 3550 ˚C

Diamond

Covalent-Network SolidsCovalent-Network Solids Graphite:Graphite:

C atoms arranged in C atoms arranged in hexagonal ringhexagonal ring

Each C is bonded to three Each C is bonded to three others in the layerothers in the layer

Good conductor of Good conductor of electricity b/c delocalized electricity b/c delocalized ππ bonds bonds

Used as lubricant and the Used as lubricant and the “lead” in pencils“lead” in pencils

Graphite

Melting point: 3652 – 3697 ˚C

Ionic SolidsIonic Solids

Ions held together by Ions held together by ionic bondsionic bonds

Strength of ionic bonds Strength of ionic bonds depend on the chargesdepend on the charges

Structure depend on Structure depend on charges and sizes of charges and sizes of ionsions

NaCl: each NaNaCl: each Na++ ion is ion is surrounded by 6 Clsurrounded by 6 Cl-- ions ions

Gray: Na. Green: Cl

Ionic Solid StructuresIonic Solid Structures ZnS: ZnZnS: Zn2+2+ ions surround ions surround

tetrahedrally by four Stetrahedrally by four S2-2- ions ions

Blue: S. Yellow: Zn

CaFCaF22: There are twice as : There are twice as many Fmany F-- ions as Ca ions as Ca2+2+ ions ions

CsCl: each CsCsCl: each Cs++ ion is ion is surrounded by eight Clsurrounded by eight Cl-- ions ions

Gray: Ca. Green: F

Gray: Cs. Green: Cl

Metallic SolidsMetallic Solids

Consist entirely of metal Consist entirely of metal atomsatoms

Each atom has 8 or 12 Each atom has 8 or 12 adjacent atomsadjacent atoms

Bonding due to delocalized valence eBonding due to delocalized valence e--

Strength of bonding Strength of bonding ↑ as # of valence e↑ as # of valence e-- ↑ ↑ Good conductors b/c of the mobility of eGood conductors b/c of the mobility of e--

Body Center-Cubic (BCC): atoms Body Center-Cubic (BCC): atoms on each corneron each corner

Atoms: Li, Na, K, Cr, Ba, etc.Atoms: Li, Na, K, Cr, Ba, etc.

Hexagonal Close-Packed (HCP): Hexagonal Close-Packed (HCP): 3 layers – top and bottom with 7 3 layers – top and bottom with 7 e-, and middle with 3 e-e-, and middle with 3 e-

Atoms: Mg, Zn, Ti, Be, etc.Atoms: Mg, Zn, Ti, Be, etc.

Metallic Bond StructuresMetallic Bond Structures

Face-Center-Cubic (FCC): atoms Face-Center-Cubic (FCC): atoms on each corner & center of each on each corner & center of each faceface

Atoms: Al, Au, Ag, Ni, Pt, etc.Atoms: Al, Au, Ag, Ni, Pt, etc.

Additional SourcesAdditional Sources http://www.science.uwaterloo.ca/~cchieh/http://www.science.uwaterloo.ca/~cchieh/

cact/c123/intermol.htmlcact/c123/intermol.html https://edocs.uis.edu/kdung1/www/https://edocs.uis.edu/kdung1/www/

Gemini/crystal_structure_visualization.htmGemini/crystal_structure_visualization.htm http://www.elmhurst.edu/~ksagarin/color/http://www.elmhurst.edu/~ksagarin/color/

discussion6.htmldiscussion6.html http://www.ndt-ed.org/http://www.ndt-ed.org/

EducationResources/CommunityCollege/EducationResources/CommunityCollege/Materials/Structure/metallic_structures.htmMaterials/Structure/metallic_structures.htm