4.5 4.5 Physical Properties in Physical Properties in

Giant Covalent SubstancesGiant Covalent Substances

Structure: Giant covalent macromoleculeGiant covalent macromolecule Bonding: Bonding: Each carbon atom has 4 bonding pairs of Each carbon atom has 4 bonding pairs of electrons and 0 lone pairs of electrons. According to electrons and 0 lone pairs of electrons. According to VSEPRVSEPR theory in order to minimize the repulsion the 4 pair theory in order to minimize the repulsion the 4 pair ofof bonding electrons repel each other equally.bonding electrons repel each other equally. Bond angle: 109.5Bond angle: 109.5oo

Shape: tetrahedral Shape: tetrahedral No intermolecular forces of attraction, only No intermolecular forces of attraction, only intramolecular attractions between the carbon intramolecular attractions between the carbon atoms.atoms.

DiamondDiamond

Physical Properties of DiamondPhysical Properties of DiamondHardness Hardest substance known Each carbon atom is held in the lattice by 4 strong covalent bonds, making diamond a strong rigid

structure. The carbon – carbon bonds can only be broken up by another diamond. Because of their hardness diamonds have many applications in industry. Parts of cars, planes, and other

machines are shaped by diamonds.

Diamond saw

Solubility in waterSolubility in water The covalent bonds between the carbon The covalent bonds between the carbon

atoms are much stronger than the force atoms are much stronger than the force of attraction exerted by polar water of attraction exerted by polar water molecules. Diamond is not soluble in molecules. Diamond is not soluble in water.water.

Melting PointMelting Point To break the strong intramolecular To break the strong intramolecular

covalent bonds requires a large amount covalent bonds requires a large amount of energy, therefore they have very high of energy, therefore they have very high temperature. temperature.

M.pt of diamond M.pt of diamond 4000 4000ooC C

Conductivity of electricityConductivity of electricity

All four outer valence electrons in in each C atom are involved in All four outer valence electrons in in each C atom are involved in forming covalent bonds with four other C atoms. Therefore the forming covalent bonds with four other C atoms. Therefore the valence electrons are not free to move making diamond a non valence electrons are not free to move making diamond a non conductor of electricity.conductor of electricity.

GraphiteGraphite Structure: Giant Covalent macromoleculeGiant Covalent macromolecule Bonding: Layers of hexagonal rings of carbon Layers of hexagonal rings of carbon

atoms. Within each layer intramolecular covalent atoms. Within each layer intramolecular covalent bonds attach each carbon atom to three other bonds attach each carbon atom to three other carbon atom. The 4carbon atom. The 4thth bonding electron is delocalized bonding electron is delocalized (mobile) and moves between the layers. These (mobile) and moves between the layers. These electrons form Van der Waal’s intermolecular forces electrons form Van der Waal’s intermolecular forces that hold the layers together.that hold the layers together.

The Physical Properties of GraphiteThe Physical Properties of Graphite

Conducts ElectricityConducts Electricity

The one electron not used in bonding is free / mobile / delocalized The one electron not used in bonding is free / mobile / delocalized and can carry a current.and can carry a current.

LubricantLubricant

The weak van der Waals forces between the layers allow them to The weak van der Waals forces between the layers allow them to slide over one another making graphite an excellent lubricant.slide over one another making graphite an excellent lubricant.

Insoluble in waterInsoluble in water

The intramolecular covalent bonds between the carbon atoms are The intramolecular covalent bonds between the carbon atoms are too strong to interact with water.too strong to interact with water.

Low densityLow density

Compared to diamond. This is because of the relatively large Compared to diamond. This is because of the relatively large amount of space between the layers. amount of space between the layers.

Soft and slipperySoft and slippery

The layers of carbon atoms slide over each other due to weak Van The layers of carbon atoms slide over each other due to weak Van der Waal’s forces between them. When you use a pencil, the layers der Waal’s forces between them. When you use a pencil, the layers of carbon atoms are rubbed off and stick to the paper. Graphite is of carbon atoms are rubbed off and stick to the paper. Graphite is one of the softest substances.one of the softest substances.

High melting point and boiling pointHigh melting point and boiling point

Mpt = 3652°C - 3697°C : b.pt = 4200°C.Mpt = 3652°C - 3697°C : b.pt = 4200°C.

Similar to diamond. To melt graphite both the intermolecular van der Similar to diamond. To melt graphite both the intermolecular van der Waals forces and intramolecular covalent bonds need to be broken.Waals forces and intramolecular covalent bonds need to be broken.

VolatilityVolatility

Not volatile Not volatile

C60 FullerenesC60 Fullerenes

Structure: Giant Covalent macromoleculeGiant Covalent macromolecule Bonding: 60 carbon atoms covalently bonded in a 60 carbon atoms covalently bonded in a

a polyhedron with 20 hexagonal (6-angled) surfaces a polyhedron with 20 hexagonal (6-angled) surfaces and 12 pentagonal (5-angled) surfaces. and 12 pentagonal (5-angled) surfaces.

Physical Properties of fullerenesPhysical Properties of fullerenes

Reactivity with other compoundsReactivity with other compoundsNot very reactive due to the stability of the carbon-carbon Not very reactive due to the stability of the carbon-carbon bonds. Chemists have been able to increase the reactivity bonds. Chemists have been able to increase the reactivity by attaching active groups to the surface.by attaching active groups to the surface.

Insoluble in many solventsInsoluble in many solvents Partial conductor of electricityPartial conductor of electricity Due to the one delocalized electron per carbon atom.Due to the one delocalized electron per carbon atom. SoftSoft

CC6060 molecules can slide over one another making them molecules can slide over one another making them softer than diamond but not as soft as graphitesofter than diamond but not as soft as graphite

VolatilityVolatilityNot volatileNot volatile

Silicon, SiSilicon, Si

Si - semimetal or metalloid element. Structure: Giant Covalent macromoleculeGiant Covalent macromoleculeBonding: Tetrahedral structure. Each silicon atom has 4 bonding Tetrahedral structure. Each silicon atom has 4 bonding

pairs of electrons and 0 lone pairs of electrons.pairs of electrons and 0 lone pairs of electrons. According to VSEPR theory in order to minimize the According to VSEPR theory in order to minimize the

repulsion between the 4 pairs of bonding electrons repulsion between the 4 pairs of bonding electrons they repel each other equally. Bond angle: 109.5they repel each other equally. Bond angle: 109.5oo. .

No intermolecular forces of attraction, only No intermolecular forces of attraction, only intramolecular attractions between the silicon atoms.intramolecular attractions between the silicon atoms.

The Physical Properties of SiliconThe Physical Properties of Silicon Does not conduct electricityDoes not conduct electricity

No delocalized valence elections to carry a current because they are all involved in bonding. Called an insulator.

HardHard

Each silicon atom is held in the lattice by 4 strong covalent bonds, giving it Each silicon atom is held in the lattice by 4 strong covalent bonds, giving it a strong rigid structure.a strong rigid structure.

Insoluble in waterInsoluble in water

The intramolecular covalent bonds between the silicon atoms are too The intramolecular covalent bonds between the silicon atoms are too strong to interact with water.strong to interact with water.

Melting pointMelting point

Lower than diamond. Si-Si bond is longer than C-C bond in diamond, Lower than diamond. Si-Si bond is longer than C-C bond in diamond, because Si has a larger radius. As the bond length increases, the amount because Si has a larger radius. As the bond length increases, the amount of energy needed to break the attractive force between the pair of of energy needed to break the attractive force between the pair of electrons in the covalent bond and the protons in the nucleus decreases. electrons in the covalent bond and the protons in the nucleus decreases.

Silicon as a semiconductorSilicon as a semiconductor Si can be made into a partial of conductor of electricity. Si can be made into a partial of conductor of electricity. Si semiconductors are found in the Si semiconductors are found in the microprocessor chips of all of all

electronic deviceselectronic devices Silicon can be made into a conductor (but not as good as a metal), by Silicon can be made into a conductor (but not as good as a metal), by

doping – adding B, P, Ga or As atoms are added to the lattice.doping – adding B, P, Ga or As atoms are added to the lattice. P and As have five valence electrons. The fifth electron does not P and As have five valence electrons. The fifth electron does not

covalently bond with the Si and remains delocalized and able to covalently bond with the Si and remains delocalized and able to conduct a current. conduct a current.

B and Ga have three outer electrons. When they bond with Si they B and Ga have three outer electrons. When they bond with Si they form a “hole” (the 4form a “hole” (the 4thth valence electron that is not involved in bonding). valence electron that is not involved in bonding). The absence of an electron on each Si atoms creates the effect of a The absence of an electron on each Si atoms creates the effect of a ppositive charge which can conduct a current. Alternatively the non ositive charge which can conduct a current. Alternatively the non bonded electrons can move from “hole” to “hole” carrying a current.bonded electrons can move from “hole” to “hole” carrying a current.

Silicon dioxide, SiOSilicon dioxide, SiO22 Naturally occurring in in the earths Naturally occurring in in the earths

crust.crust. Each Si atom is linked to four O Each Si atom is linked to four O

atoms, and each O to two Si atoms atoms, and each O to two Si atoms in a 1:2 ratio. Bent shape.in a 1:2 ratio. Bent shape.

Physical Properties:Physical Properties: High melting point (1650 - 1730 High melting point (1650 - 1730

°C) and boiling point°C) and boiling point insoluble in waterinsoluble in water not volatilenot volatile does not conduct electricitydoes not conduct electricity

Silicone bake wareSilicone bake ware Synthetically manufactured rubber like polymer containing Synthetically manufactured rubber like polymer containing

silicon and oxygen.silicon and oxygen.

Properties that make it useful for baking:Properties that make it useful for baking: durable and long lasting durable and long lasting Soft and flexibleSoft and flexible Doesn’t break like glass, or ceramic (other silicon based Doesn’t break like glass, or ceramic (other silicon based

substances)substances) Does not dent or rust like metalDoes not dent or rust like metal Lightweight Lightweight Does not react with foodDoes not react with food Can withstand high tempCan withstand high temp

Silicone Breast Silicone Breast ImplantsImplants

Synthetically manufactured rubber sac filled with silicon gel like Synthetically manufactured rubber sac filled with silicon gel like polymer containing silicon and oxygen atoms.polymer containing silicon and oxygen atoms.

Properties that make is useful for breast Properties that make is useful for breast

implants:implants: Soft, flexible and tactileSoft, flexible and tactile Stable at all temperaturesStable at all temperatures Long lastingLong lasting Won’t react with other chemicals in the bodyWon’t react with other chemicals in the body Despite silicones chemical and physical stability some women’s Despite silicones chemical and physical stability some women’s

bodies have rejected the silicone implants resulting in many law bodies have rejected the silicone implants resulting in many law suits in the US and concerns about their safety.suits in the US and concerns about their safety.

BibliographyBibliography

http://chemcases.com/silicon/sil15one.htmhttp://chemcases.com/silicon/sil15one.htm