structure and properties of solids

8/2/2019 Structure and Properties of Solids

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A solid is one of the three classical states of matter Solids can be classified into 2 types:

Crystalline (regular geometric lattice) Amorphous (irregular arrangement w/ no pattern/lattice)

All solids have a definite shape and volume, are virtuallyincompressible, & do not readily flow because the atoms in asolid are tightly bound to each other

Hardness, melting point, mechanical characteristics,conductivity of solids can vary

Structure and properties related to FORCES BETWEEN THEPARTICLES

Forces are all electrostatic (interaction between +ve and vecharges) but vary in strength


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Crystals consist of a pattern of repeating cell units ina 3D structure

Crystal lattice is a regular, repeating pattern ofatoms, ions, or molecules in a crystal

Crystalline solids can be further classified by theirdistinct properties and chemical bonding

Class of Substance ElementsCombined

Examples

Ionic Metal + Nonmetal NaCl(s) , CaCO3(s)

Metallic Metal(s) Cu(s), CuZn(s)

Molecular Nonmetal(s) H20(s), CO2(s)

Covalent Network Metalloids/carbon C(s) , SiC(s)


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Molecular

Solids

Covalent Solids Ionic solids

Metallic solids

Na+

Cl-


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NaCl, or table salt is an example of an ionic crystal. The properties of ioniccrystals are explained by a 3-D arrangement of positive and negative ions heldtogether by strong, directional ionic bonds.


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Ionic compounds are formed when a metal gives up its valenceelectrons to a nonmetal to gain stability and form ions

These ions are held together in a 3D crystal lattice structure becauseof the simultaneous attraction of an ion by the surrounding ions of

opposite charge The distance between the nuclei of adjacent ions in a crystal

(interionic distance) is determined by the tendency of the ve- torepel each other

Theres a greater force of attraction since its made of full chargeions not partial charge polar molecules, which is why ionic bondingis much stronger than any IMF


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Ionic crystals are relatively hard and brittle (SATP), conduct electricity (ONLY inliquid state), & have high melting points (due to high crystal energy)

These properties prove that ionic bonds are:

Strong electrostatic attractions between ve and +ve ions, require a lot of

energy to overcome them(hardness,MP)

The greater the charge on the ions, the stronger the attraction; higher mp

Also, the smaller the ions, the closer together they are, the greater theattraction, but if ions are bigger, attraction is less and less heat is needed toseparate them (Sodium > Rubidium)

Directional, packed in a certain way so they split at an angle (brittleness)

-because of the highly directional bonds, if something (pressure) shifts the ion layersslightly, the ions of the same charge repel each other, and the crystal breaks (repels

itself to pieces)

And that the lattice is formed of ions (electrical conductivity)

Cannot conduct as a liquid because e- not free to move

As a liquid, irons dissociate; e- free to move and conduct


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SOLUBLE IN POLAR SOLVENTS

Not soluble in non-polar solvents

The attractions between the solvent molecules andthe ions aren't big enough to overcome the attractions

holding the crystal together


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Gold, copper and silver are examples of metals made up of metalliccrystals. The properties of metallic crystals are explained by a 3-Darrangement of metal cations held together by strong,nondirectional bonds created by a sea of mobile electrons.


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Metallic crystals refers to elements and alloys of metals

X-ray diffraction patterns show that metals have a continuousand compact crystalline structure

The electron sea theory is most accepted because it can explain

all the properties of metals It states that the properties of metals are the result of the

bonding between fixed, positive nuclei, and loosely held, mobilevalence electrons

The attraction is not localized or directed for specific atoms

The electrons acts as a negative glue surrounding the positivenuclei Electron sea model incorporates:

low IE ve- are loosely held Mobility empty valence orbitals

Electrostatic sea strong, non directional bonding


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Metallic crystals are shiny and silvery

Because their valence electrons are subject to the photoelectric effect, where the ve- absorb

and re-emit energy from all of visible/near visible light

Flexible - ductility (wire) /malleability (sheets)

Nondirectional bonds allow planes of atoms to slide over each other without breaking bonds

Electrical Conductivity

ve- move freely through the metal

A battery can force additional e- onto one end of a metal sample and remove e- from theother end

Hardness/ high MP (varies due to size of atom)

Electron sea around positive nuclei = strong bonding

More e- and higher positive charge = stronger metallic bond

The strength of the bond varies from metal to metal and depends on the number of

electrons which each atom delocalises into the sea of electrons, and on the packing

Group 1 metals like sodium and potassium have relatively low melting and boiling pointsmainly because each atom only has one electron to contribute to the bond, in efficient

packing (8 co-ord)

Crystalline structure

Electron sea holds atomic nuclei together, this produces structures that are continuous and

closely packed


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Molecular solids are made up of one or more non-metals

Non metals come together and form covalent bonds by sharing electrons tobe more stable

Can be polar or non-polar molecular crystals The covalent bonds holding the molecules together are very strong, but

physical properties of the substance are dependant on the intermolecularforces - forces attracting one molecule to its neighbours, which are weaker


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Solid carbon dioxide is an example of a molecular crystal.The properties of molecular crystals are explained by a 3-D arrangement of neutral molecules held together byrelatively weak intermolecular forces.


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they normally have a low MP, are soft, and are non-conductors

Properties can be explained by IMF: Low MP/

You don't have to break any covalent bonds in order to melt or boil amolecular substance.

lack of hardness London, dipole-dipole, H bonds are weak

Attraction between molecules is not strong

Lack of conductivity individual particles are neutral molecules, even inmolten state, molecules to not break up into ions

Molecular Molecules London,

dipole-dipole,

hydrogen

-soft

-low MP

-non-conductors

- like dissolves like in terms of

solubility

H20(s), CO2(s)(ice, solid

carbon

dioxide)

CRYSTAL PARTICLES FORCE/BOND PROPERTIES EXAMPLE


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Crystals consist of a pattern of repeating units

X-ray analysis shows that they have a crystal lattice like ionic compoundsbut the molecules are packed as closely as size/shape allows (morecomplicated)


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Quartz and Amethyst are examples of CNC. Theproperties of network covalent crystals are explainedby a 3-D arrangement of atoms held together bystrong, directional covalent bonds.


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Covalent network crystals are among the hardest materials onearth

they are also brittle (rarely brake, dont bend under pressure),

have high melting points (higher than ionic/molecular crystals),are insoluble, & are non-conductors

These solids consist of large networks of covalent bonds thatform a long-range, regular crystalline structure, called a covalent

network Most covalent networks involve the elements and compounds of

carbon and silicon


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Hard - the individual bonds in a covalent network crystal (ex. C-Cbond) are not that strong on their own, the overall bonding inthe large macromolecule is very strong

High MP - To melt a covalent network crystal, many bonds mustbe broken with lots of energy

Lack of conductivity electrons are held tightly between theatoms or in covalent bonds, they are not free to move through

the network Many are insoluble in water and organic solvents

There are no possible attractions which could occur betweensolvent molecules and carbon atoms which could outweighthe attractions between the covalently bound carbon atoms.


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Solids that are arranged in 3-D arrays because oftheir covalent bonds

The strong bonds in these solids cause them to

have very high melting and boiling points, solidsat room temperature, hard, insoluble and arenon-conductors of electricity

(Eg Diamond, Quartz, silicon carbide)


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Belongs to 3-D dimensional group The silicon atoms form a tetrahedral shape when bonded to four oxygen

atoms Quartz is used for metal ions within substances that produces well known

stones such as emerald, amethyst and garnet

SiO2(s) - (in the form of quartz) has a regular network covalent crystallinestructure which makes it hard and gives it a high MP But as glass, it is not crystalline because it lacks order, and does not have the

properties of a covalent network crystal (it is purposely cooled to a rigid state) Although they have the same formula, their properties are GREATLY effected

by the structure their molecules form


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Solids that form 2-D network sheets, the sheets are held by covalent bonds

The layers are held by weak Van der Waals forces

These solids have high melting and boiling points, however they are soft enoughto be used as lubricant

Eg( Graphite, Mica)

2-Dimensional sheets of silicate

The weak forces between the layers of mica is why this substance breakseasily


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Solids that only form one dimensional networks Forces between the chains are very weak

However they have high melting and boiling points, are solids at roomtemperature and are insoluble

Belong to 1-Dimensional network solids group, asbestos are very stringy

Asbestos were used in fire extinguishers to put out fires, however studieshave now shown that asbestos can lead to lung cancer


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Elements that can exist with different physicalforms and properties but will all have the exact

same chemical properties.

Eg( Diamond, and Graphite)


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Carbon is able to bond to many different molecules andcan bond with itself to form pure carbon substances

Carbon can form 3-D tetrahedral arrangements(diamonds), layers of sheets (graphite) large sphericalmolecules (buckyballs) and long thin tubes (nanotubes)

The structures of eight allotropes of carbon: (A) Diamond [3D, network covalent structure] (B) Graphite [2D, covalent plates] (graphene is a single of graphite) (C) Lonsdaleite (D) C60 [0D, molecules] (Buckminsterfullerene or buckyball) (E) C540 Fullerene (F) C70 Fullerene (G) Amorphous carbon (H) Single-walled carbon nanotube [1D, tubes] (buckytube).


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Using x-ray diffraction we can see that diamonds have carbon atomsin a large tetrahedral network with a Carbon bonded to 4 other Carbonatoms.

Diamond is one of the strongest substances in the world due to strongcovalent bonds.

Its properties can be explained by the 3-D arrangement of atoms heldtogether by strong, directional covalent bonds that from a network


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Using x-ray diffraction we can see that diamonds have carbon atomsin a large tetrahedral network with a Carbon bonded to 4 other Carbonatoms.

Its properties can be explained by the 3-D arrangement of atoms heldtogether by strong, directional covalent bonds that from a network

Diamond is one of the strongest substances in the world due to strongcovalent bonds.

It is so hard it can be used to make drill bits, and to cut other diamonds

VERY HIGH MP

Diamonds do not have delocalized electrons so they do not conductelectricity

The planes inside the crystal of a diamond allows light to be reflected,giving the diamond its sparkle.


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Unlike most CNC graphite can conduct electricity and acts as a lubricant butstill has a high MP/is hard

Graphite belongs to the 2-D network solids X-ray diffraction shows that graphite is made of hexagonal sheets of sp2

hybridized carbon atoms These planar sheets are strong covalent networks but the bonding between

the sheets is weak London dispersion forces, which allows for graphite's

lubricating properties (layers of graphite are able to slide past each other) The delocalized electrons in graphite move freely allowing electricity to pass

through. When we write with a pencil we are splitting the layers of graphite, not

breaking the sheets


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Transistors are used in almost everything electronic (asolid state sandwich of crystalline semi conductors)

In a semiconductor an atom only requires a small amount

of energy to jump to the next highest energy level

Semiconductors, are very useful and are used for many

things such as power cells in satellites and for the ISS

These semiconductors are able to convert electricity to

light, heat to electricity and vice versa

Transistor -> increases flow of electricity; resistor impedes

(decreases) it


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Basically in a conductor empty orbitals and valence orbitalsare at same energy so e- can easily be transported

throughout the solid In an insulator there is a large energy gap between

empty/valence orbitals so e- cannot easily get to theseconducting orbitals

In a semi conductor there is a small energy gap between thevalence/empty orbitals; thermal energy can easily promotesome e- into the empty orbitals to provide conductivity


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By adding chemicals to semiconductors we can make them work indifferent ways.

This is called doping

Semiconductors in transistors are covalent crystals that have been

manipulated (silicon or germanium + small quantity of group 13/15element)

For example, doping silicon with a small fraction of phosphorus, (whichhas one more ve-) , there are more e- for conduction, increasing theconductivity

Or with Boron (one ve- less than silicon) in this case, since there is oneless electron, an electron vacancy or hole is created

As an electron fills this hole, it leaves a new hole, and this keeps going on(hole goes opposite the electrons) the charge moves along resulting inconduction


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CRYSTAL PARTICLES FORCE/BOND PROPERTIES EXAMPLE

Ionic Ions (+/-) Ionic bonding -hard-brittle

-high MP

-conductor (as liquid/aq state)

-many are water soluble

NaCl(s) (tablesalt)

Metallic Cations (+)

surroundedby sea ofelectrons (-)

Metallic

bonding

-characteristic lustre

-soft to hard-flexible (ductile, malleable)-conductors

-dissolve in other metals to form alloys

Au(s) , Ag(s) ,

Cu(s) (coinagemetals)

Molecular Molecules London,

dipole-dipole,

hydrogen

-soft

-low MP

-non-conductors- like dissolves like in terms of

solubility

H20(s), CO2(s)(ice, solid

carbondioxide)

CovalentNetwork

Atoms Covalent -very hard-very high MP

-non-conductors

-insoluble in most liquids

C(s) , SiO2(s)(carbon,

silicon dioxide)


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Metallic Crystals

Network Crystals

Molecular Crystals

* I i l f d h l d l ( l i i )

structure and properties of solids

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