Presentation on theme: "4.5 Physical Properties in Giant Covalent Substances"— Presentation transcript:
14.5 Physical Properties in Giant Covalent Substances
2Diamond Structure: Giant covalent macromolecule Bonding: Each carbon atom has 4 bonding pairs ofelectrons and 0 lone pairs of electrons. According to VSEPRtheory in order to minimize the repulsion the 4 pair ofbonding electrons repel each other equally.Bond angle: 109.5oShape: tetrahedralNo intermolecular forces of attraction, onlyintramolecular attractions between the carbon atoms.
3Physical Properties of Diamond HardnessHardest substance knownEach 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
4Solubility in waterThe covalent bonds between the carbon atoms are much stronger than the force of attraction exerted by polar water molecules. Diamond is not soluble in water.Melting PointTo break the strong intramolecular covalent bonds requires a large amount of energy, therefore they have very high temperature.M.pt of diamond 4000oC
5Conductivity of electricity All four outer valence electrons in in each C atom are involved in forming covalent bonds with four other C atoms. Therefore the valence electrons are not free to move making diamond a non conductor of electricity.
6Graphite Structure: Giant Covalent macromolecule Bonding: Layers of hexagonal rings of carbon atoms. Within each layer intramolecular covalent bonds attach each carbon atom to three other carbon atom. The 4th bonding electron is delocalized (mobile) and moves between the layers. These electrons form Van der Waal’s intermolecular forces that hold the layers together.
7The Physical Properties of Graphite Conducts ElectricityThe one electron not used in bonding is free / mobile / delocalized and can carry a current.LubricantThe weak van der Waals forces between the layers allow them to slide over one another making graphite an excellent lubricant.Insoluble in waterThe intramolecular covalent bonds between the carbon atoms are too strong to interact with water.Low densityCompared to diamond. This is because of the relatively large amount of space between the layers.
8Soft and slipperyThe 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 of carbon atoms are rubbed off and stick to the paper. Graphite is one of the softest substances.High melting point and boiling pointMpt = 3652°C °C : b.pt = 4200°C.Similar to diamond. To melt graphite both the intermolecular van der Waals forces and intramolecular covalent bonds need to be broken.VolatilityNot volatile
9C60 Fullerenes Structure: Giant Covalent macromolecule Bonding: 60 carbon atoms covalently bonded in a a polyhedron with 20 hexagonal (6-angled) surfaces and 12 pentagonal (5-angled) surfaces.
10Physical Properties of fullerenes Reactivity with other compoundsNot very reactive due to the stability of the carbon-carbon bonds. Chemists have been able to increase the reactivity by attaching active groups to the surface.Insoluble in many solventsPartial conductor of electricityDue to the one delocalized electron per carbon atom.SoftC60 molecules can slide over one another making them softer than diamond but not as soft as graphiteVolatilityNot volatile
11Silicon, Si Si - semimetal or metalloid element. Structure: Giant Covalent macromoleculeBonding:Tetrahedral structure. Each silicon atom has 4 bonding pairs of electrons and 0 lone pairs of electrons.According to VSEPR theory in order to minimize the repulsion between the 4 pairs of bonding electrons they repel each other equally. Bond angle: 109.5o.No intermolecular forces of attraction, only intramolecular attractions between the silicon atoms.
12The Physical Properties of Silicon Does not conduct electricityNo delocalized valence elections to carry a current because they are all involved in bonding. Called an insulator.HardEach silicon atom is held in the lattice by 4 strong covalent bonds, giving it a strong rigid structure.Insoluble in waterThe intramolecular covalent bonds between the silicon atoms are too strong to interact with water.Melting pointLower 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 of energy needed to break the attractive force between the pair of electrons in the covalent bond and the protons in the nucleus decreases.
13Silicon as a semiconductor Si can be made into a partial of conductor of electricity.Si semiconductors are found in the microprocessor chips of all electronic devicesSilicon 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.P and As have five valence electrons. The fifth electron does not covalently bond with the Si and remains delocalized and able to conduct a current.B and Ga have three outer electrons. When they bond with Si they form a “hole” (the 4th valence electron that is not involved in bonding). The absence of an electron on each Si atoms creates the effect of a positive charge which can conduct a current. Alternatively the non bonded electrons can move from “hole” to “hole” carrying a current.Remember ions or delocalized electrons or ions are needed to conduct a current. Si semiconductors come in two types p and n. Silicon valley. Silicon chip – small square of Si semiconductor.
14Silicon dioxide, SiO2 Naturally occurring in in the earths crust. Each Si atom is linked to four O atoms, and each O to two Si atoms in a 1:2 ratio. Bent shape.Physical Properties:High melting point ( °C) and boiling pointinsoluble in waternot volatiledoes not conduct electricity
15Silicone bake wareSynthetically manufactured rubber like polymer containing silicon and oxygen.Properties that make it useful for baking:durable and long lastingSoft and flexibleDoesn’t break like glass, or ceramic (other silicon based substances)Does not dent or rust like metalLightweightDoes not react with foodCan withstand high temp
16Silicone Breast Implants Synthetically manufactured rubber sac filled with silicon gel like polymer containing silicon and oxygen atoms.Properties that make is useful for breastimplants:Soft, flexible and tactileStable at all temperaturesLong lastingWon’t react with other chemicals in the bodyDespite silicones chemical and physical stability some women’s bodies have rejected the silicone implants resulting in many law suits in the US and concerns about their safety.The first implants were a silicon bag filled with salt water – saline implants