crystal properties by abhishek jaguessar

8/4/2019 Crystal Properties by Abhishek Jaguessar

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CRYSTAL PROPERTIES

BY

ABHISHEK JAGUESSAR



Ionic, HIonic, H--bonding, Dipole, or London?bonding, Dipole, or London?

Details Bond Molecule IMF

(EN = 0 - 0.5 nonpolar nonpolar London(EN = 0.5 - 1.7 polar polar dipole-dipole*

(EN = 1.7 - 3.2 ionic Ionic ionic*

H + N,O,F polar polar H-bonding*

Symmetrical

molecule (any (EN)-- nonpolar London

*Since all compounds have London forces. London*Since all compounds have London forces. London

forces are also present. However, their affect is minor forces are also present. However, their affect is minor and overshadowed by the stronger forces present.and overshadowed by the stronger forces present.Note: the term ³polar´ is used interchangeable withNote: the term ³polar´ is used interchangeable with³polar covalent´. Likewise, ³nonpolar´ and ³nonpolar ³polar covalent´. Likewise, ³nonpolar´ and ³nonpolar

covalent´ mean the same thing.covalent´ mean the same thing.



Network solids (covalent crystals)Network solids (covalent crystals)� There are some compounds that do not

have molecules, but instead are long chainsof covalent bonds (E.g. diamond)

C C C

C C C

C C C C C

C

C CCC

C

� This happens in 3 dimensions, creating acrystal

� Because there are only covalent bonds,

network solids are extraordinarily strong



Metallic crystalsMetallic crystals� Metals normally occur as solids (high

melting points).� Thus, there must be strong bonds between

the atoms of metals causing them to bond� Bonding in metals and alloys is different

from in other compounds: positive nucleiexist in a sea of electrons (this explains whymetals conduct electricity)

+

+

+

+

+

++

+

+ ±

±

±

±

± ±

±

±

±

±

± ±

± ± ±

±

± ±



Crystal typesCrystal types� There are 6 types of intermolecular forces

� These forces are associated with certaincrystal types. By comparing solids we have

a common frame of reference.

� The crystal types and their basic units are1) Network (covalently bonded atoms)

2) ionic (electrostatic attraction of ions),

3) metallic (positive nuclei in electron sea),

4) Molecular (electrostatic attraction of

dipoles in molecules)

a) Polar (dipole-dipole and H-bonding)

b) Non-polar (London forces)



Properties of crystalsProperties of crystals� Boiling and melting occur when the forces

between molecules are overcome and achange of state occurs

� The higher the force of attraction between

molecules (IMF) the higher the melting/-boiling point (see previous slide for order )

� Only metallic crystals conduct electricity in

solid state (they also conduct in liquid state)

� Ionic crystals will conduct electricity in

molten state or dissolved because ions are

free to move to positive and negative poles



Solubility of crystal typesSolubility of crystal types� Solute = what is dissolving (e.g. salt)

� Solvent = what it is dissolving in (e.g. water )

� Strong attractions between the basic units of

covalent crystals cause them to be insoluble.

� Metallic crystals are likewise insoluble� The solubility of other crystals depends on

solute and solvent characteristics

� We will see that polar/ionic solutes dissolvein polar/ionic solvents and non-polar solutes

dissolve in non-polar solvents

� This is known as the like-dissolves-like rule



Attraction and randomness Attraction and randomness� The reason why some substances mix and

others do not has to do with «1) Intermolecular forces2) the tendency for randomness due to

random molecular motion

� Reference: 499 (starting from ³ A tendencytoward randomness´) to 502 (ending right

before ³How Soaps and Detergents work´)



Mixing oil and water Mixing oil and water � Lets take a look at why oil and water don¶t

mix (oil is non-polar, water is polar )

H+

H ±H+ H+

H ±H+

H+

H ±H+

H+

H

±H+ H+

H ±H+

H+

H ±H+

H+

H ±H+

H+

H

±H+

The dipoles of water

attract, pushing the oil(with no partial charge)

out of the way: attractionswin out over the tendency

toward randomness



Crystals worksheetCrystals worksheet� Place numbers in boxes according to

descriptions� Use pg. 374-376 and class notes, and

internet as references� At end rows should add up to 126 each



Crystals worksheet answersCrystals worksheet answers

P A M E T C E

Metallic 2 7 13 16 23 30 35

Network 3 10 11 20 21 29 32

Ionic 5 8 12 17 24 27 33

Molecular polar 4 9 14 18 22 28 31

Molecular

non-polar

1 6 15 19 25 26 34

crystal properties by abhishek jaguessar

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