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Presentation On Metallic Bonding

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Published in: Chemistry
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This presentation describes on: i. intermolecular forces ii. instantaneous dipole induced dipole forces iii. permanent dipole dipole forces iv. water is peculiar

Athumani R / Dubai

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  1. METALLIC BONDING PREPARED BY: ATHUMANI R KAWAMBWA PHARMICIST (BPHARM)
  2. OUTLINES Introduction Intermolecular Forces Instantaneous Dipole-induced dipole forces Permanent dipole-dipole forces Water is Peculiar
  3. Metals have different properties to both ionic and covalent compounds. In appearance they are usually shiny They are good conductor of both heat and electricity. They are usually worked and drawn into a wire or hammered into different shapes. They are ductile and malleable
  4. Metals possess high tensile strengths and they are usually hard. Because of these properties human use them to make different tools, weapons and jewelry. In metallic lattice, the atoms lose their outermost shell electrons to become positive ions. The outer shell electrons occupy new energy levels, which extend throughout the metal lattice.
  5. The bonding is often described as a 'sea' of mobile electrons surrounding the lattice of positive ions. DIAGRAM OF METALLIC BONDING
  6. The lattice is held together by strong attractive force between the mobile electrons and the positive ions. Electrical conduction can take place in any direction, as electrons are free to move throughout the lattice. Conduction of heat occurs by vibration of positive ions as well as via mobile electrons. Metals are both ductile and malleable because the bonding in metallic lattice is not broken down when they are physically deformed.
  7. As the metal is hammered or drawn into a wire, the metal ions slide over each other to a new lattice positions. The mobile electrons continue to hold lattice together. Some metals will even flow under their own weight. Lead has a problem on hammering, it has been used as a roof over years. It suffers from 'creep'. This is because lead flow slowly under gravitational force.
  8. Transitional metals are both hard and have high tensile strength. High tensile strength and hardness is due to strong attractive forces between metal ions and the mobile electrons in the lattice.
  9. PROPERTIES OF SOME METALS AND SULFUR ELEMENT cu DENSITY (gcm-3) 2.7 7.86 8.92 2.07 TENSILE STRENGTH (1010 Pa) 7.0 21.1 13.0 THERMAL ELECTRICAL CONDUCTIV CONDUCTIV ITY (W/mK) 238 82 400 0.029 ITY (108 S/m) 0.38 0.10 0.59 Ix 10-23
  10. QUIZ Use the table in the last slide to answer the following questions and give out their fully explanation. (Assume that steel and stainless steel have the same properties as iron) a. Why some stainless steel saucepan have a copper base? b. Aluminium with steel core is used for overhead power cables in preference to copper, why is Aluminium preferred? What is the function of steel core? c. Copper is chosen for almost all other electrical uses. Suggest a reason for the choice of copper?
  11. INTERMOLECULAR FORCES On reviewing states of matter In solid state, the particles are closely packed together in regularly ordered way. This order breaks when solid melts. In liquid state, there may be small group of particles with some degree of orders, but overall in liquid, particles are free to move past each other. In gaseous state, the particles move randomly in any direction, as they do so, they exert pressure on the wall of container.
  12. multitude of biochemical compounds are involved in enormous number of chemicals reaction found in the living things. They are also responsible for a seemingly infinite numbers of variations within given species. All biochemical compounds rely significantly on a weak attractive force that exist between their molecules to produce this variety. The intermolecular forces are called van der Waal forces which are weaker than ionic, covalent or metallic bonding forces.
  13. The properties of all small molecules depend on intermolecular forces. It is property of these small molecules that provide evidence for the existence of intermolecular forces of and helps us to understand nature of this force. If a gas is able to condense to liquid, which can be frozen to solid, there must be an attraction between these molecules of the gas. When solids melt or liquids boil, energy is needed to overcome this attraction.
  14. For example, water in a kettle will continue to boil only whilst the electricity is switched ON. The temperature of water is constant whilst the water is boiling, and the heating effect of energy from the electricity is separating the water molecules from each other to produce water vapour.
  15. There are three types of intermolecular forces, namely: Instantaneous dipole — induced dipole forces ii. Dipole— dipole forces iii. Hydrogen bonds l. INSTANTANEOUS DIPOLE - INDUCED DIPOLE FORCES Even noble gas atoms must exert attractions on each other. Enthalpy of vaporization of noble gases increases from helium to xenon as the number of electrons increases.
  16. Alkanes also show similar trends as noble gases. Enthalpy of vaporization This is the energy required to convert liquids into the gases. Both noble gases and alkane have attractive forces between atoms and molecules, which are now known to depend on number of electrons and protons present. the attractive forces arise because electrons in atoms or molecules are moving at very high speed in orbitals.
  17. At any instant in time it is possible for more electrons to lie to one side of atom or molecule tan the other, when this happens an instantaneous electric dipole occurs. The momentary imbalance of electrons provides the negative end of a dipole, with atomic nucleus providing the positive end of the dipole. This instantaneous dipole produces an induced dipole in a neighbouring atom or molecule, which is hence attractive. This is rather like effect of a magnet (magnetic dipole) on a pin. The pin becomes temporary magnetized and it is attracted to the magnet. Intermolecular forces of this type are called van der Waal forces or instantaneous dipole — induced dipole forces.
  18. The strength of van der Waal forces increases with increase in number of electrons and protons present. Instantaneous dipole — induced dipole forces are the weakest type of attractive forces found between atoms or nucleus. They are responsible for slippery nature of graphite, which is contrast to the great hardness of diamond and volatility of bromine and iodine.
  19. POLYMER Polymer is the large molecule built up from large number of small molecules called monomers. The differences in many properties of polymers depend on the way that polymer molecules (monomers) are packed. Example of polymers: High Density Poly(Ethene), HDPE Low Density Poly(Ethene), LDPE
  20. HDPE Hight Density Poly(Ethene) .•HDPE molecules can pack much more closely as they are not branched. This causes HDPE to have stronger instantaneous dipole — induced dipole forces. HDPE is made using catalyst developed by Swiss chemist Ziegler nad Italian chemist Natta.
  21. In HDPE, the polymer chains are arranged in a much more regular fashion. This increases the density of materials and makes it more opaque to light. As molecules are closer together in HDPE, the instantaneous dipole — induced dipole forces between non — polar poly(ethene) molecules are greater and the tensile strength of materials is higher.
  22. STRUCTURE OF ??? DENSlTY POLY(ETHENE) ??? ?? ?? -—??? ??? ???
  23. Low Density Poly(Ethene) LDPE molecules are branched at intervals, which prevent them packing as closely. • That results LDPE to have weaker instantaneous dipole — induced dipole forces. • LDPE is made under high pressure with trace of oxygen as catalyst. The product consists of primarily of a tangled mass of polymers chains with some regions where the chain have some alignment.
  24. THE STRUCTURE OF LOW DENSITY POLY(ETHENE) Low Density Polyethylene (LDPE) Chemical Structure CH2 CH2 CH2
  25. The diagram of crystalline and non crystalline regions in poly(ethene). LDPE has fewer of the crystalline regions than HDPE. In the crystalline regions, polymer chains lie parallel to each other. CRYSTALLINE AND NON CRYSTALLLINE REGIONS IN POLY(ETHENE) ITS
  26. TEFLON Teflon is poly(tetrafluoroethene), PTFE The instantaneous dipole — induced dipole forces between oil or grease and PTFE are much weaker than those present in oil or grease itself. This gives rise to polymer non stick properties.
  27. STRUCTURE OF INDUCED DIPOLE ATTRACTIONS Water (polar) -6 Oxygen (induced dipole)
  28. THE STRUCTURE OF GRAPHITE In the planar sheets of carbon atoms, all the bonding electrons are involved in the covalent bonds. The sheets are held together by much weaker instantaneous dipole — induced dipole forces.
  29. The forces are easily overcome, allowing the sheets to slide over each other, rather like a pack of cards. For this property graphite is often used as lubricant.
  30. THE STRUCTURE OF DIAMOND In contrast to graphite, each carbon atom in diamond forms four covalent bonds to other four carbon atoms.
  31. The resulting network of covalent bonds requires considerable energy to separate the atoms. The strength of bonding in diamond is responsible for its greater hardness.
  32. ll. PERMANENT DIPOLE - DIPOLE FORCES A nylon rod may be given charge of static electricity by rubbing it with dry sheet of poly(ethene). If this is brought near a fine jet of water, the stream of water is attracted by the charge on the nylon rod. TRY THIS: Use a nylon/plastic comb and a fine trickle of water from tap.
  33. The water molecules are attracted to the charged nylon rod or comb because they have permanent electric dipole. A force of this type is called dipole — dipole force. The dipole of water rises because of the bent shape of the molecule and greater electron charge around the oxygen atom.
  34. DEFFLECTION OF WATER BY ELECTRICALLY CHARGED NYLON COMB
  35. A molecule is often polar if its atoms have different electronegativities. The diagram below shows the lone-pairs and electric dipole of sea water molecules ELECTRIC DIPOLE AND LONE PAIR OF SEA WATER
  36. QUIZ 1. The nylon rod carries a positive charge. Which end of water molecule is attracted to the rod, why are no water molecules repelled to the rod? A ply(ethene) rod may be given a negative charge when rubbed with nylon cloth. Will the charge of poly(ethene) rod attract or repel a thin stream of water?
  37. POLY(ESTER) CHAIN Many fabrics are made using poly(ester) fibre because of that polymer strength. SECTION OF POLY(ESTER) MOLECULE o o o Polyesters —CH2-CH2 n
  38. The strength of poly(ester) fibre is due to the strength of dipole — dipole forces between ester groups of adjacent molecules. QUIZ 1. Draw a section of poly(ester) as shown in the past slide and mark the polar groups showing 5+ and 6- charges. 2. Draw a second section of poly(ester) as shown in (1) and mark dipole — dipole forces with dotted line.
  39. WATER IS PECULIAR The boiling point of water is also much higher than predicted by the trend in boiling points for other hydrides of group VI elements. • This trend would suggest that water should be gas at room temperature and pressure. There are several more ways in which water behaves differently to most other liquids. For example: It has a very high surface tension and high viscosity. The density of ice is less than the density of water.
  40. Most solids are denser than their liquids, as molecules usually pack closer in solids than in liquids. TRENDS IN ENTHALPY CHANGES OF VAPORISTAION FOR GROUP VI HYDRIDES 300 Has H,Te 120 Molecular rnass
  41. QUIZ 1. Explain the underlying increase in the enthalpy changes of vaporization with increasing atomic numbers. 2. Estimate a value for water based on their trends. 3. What is the cause of much higher value observed for water?
  42. HYDROGEN BONDS *The peculiar nature of water is explained by the presence of strongest type of intermolecular force that is hydrogen bond. Water is highly polar owing to large difference in electronegativity between hydrogen and oxygen. The resulting intermolecular attraction between oxygen and hydrogen atoms on neighbouring water molecules is very strong dipole - dipole attraction called hydrogen bond. Each water molecule can form two hydrogen bonds to other water molecules. These form in the direction of lone pairs.
  43. In the liquid state, water molecules collect in groups. On boiling, the hydrogen bonds must be broken down. This raises the boiling point of significantly as the hydrogen bonds are stronger than the other intermolecular forces. Similarly the enthalpy change of vaporization is much higher than it would be if no hydrogen bonds were present. In ice, a three dimensional hydrogen bonded lattice is produced. In this lattice, each oxygen is surrounded by a tetrahedron of hydrogen atoms bonded to further oxygen atoms.
  44. The extensive network of hydrogen bonds raises the freezing point significantly above the predicted by the trend for other hydrides of group VI elements.
  45. MODEL OF ICE
  46. The high surface tension of water is explained by the presence of hydrogen bonded network of water molecules at the surface. This network is sufficiently strong to enable a needle to be floated on the surface of water. Within the bulk of water, small groups of molecules are attracted by hydrogen bonds. The hydrogen bonds are constantly breaking and reforming at the room temperature. As the temperature of water is raised toward the boiling point, the number of hydrogen bonds reduce. On boiling the remaining hydrogen bonds are broken down . Water vapour consists of widely separated water molecules.
  47. QUIZ 1. Why does a needle float on water sink on the addition of washing — up liquid to the water? 2. A diamond type lattice is present in ice. The O-- --H hydrogen bond is 0.159 nm and the O —H covalent bond length is 0.096 nm. When the ice melts, some hydrogen bonds break and the density rises, explain why ice has lower density than water?
  48. 3. The boiling points for group V elements hydrides are as follows: HYDRIDE Ammonia NH3 Phosphine PH3 Arsine AsH3 Stibine SbH3 Bismuthine BiH3 BOILING POINTS (K) 240 185 218 256 295 Plot a graph of those boiling points against the relative molecular masses of hydrides a. Explain the steady rising trend in the boiling point from phosphine to bismuthine b. Explain why the boiling point of ammonia does not follow this trend?
  49. This synthetic polymer is an example of poly(amide) It is similar to poly(ester) with the — O — link replaced by — NH — link. The structure section of the polymer chain of one type of nylon is shown below. O Structure of Nylon - 6.6 n
  50. The — CO — NH — link is called an amide, hence the name polyamide) Nylon fibers are produced in the same way as poly(ester) fibers. Their high tensile strength is due to strong hydrogen bonds forming between —NH— hydrogen atoms and a C = O oxygen atom on neighbouring polymer chain. The structure of a section of nylon 6,6 Each monomer unit contains six carbon atoms, hence the name nylon—6,6.
  51. THE DIAGRAM OF NYLON -6 6 Structure of Nylon - 6,6
  52. MODEL OF THE DNA HELIX FORMED BY PROTEIN MOLECULE
  53. Not all the polymer chains lie close and parallel when fibers are stretched, the molecules straighten further but are held together by hydrogen bonds, which return the molecules to the original positions on release. The combinations of strength and high elasticity are important properties in climbing rope. If a climber falls, a nylon rope can stretch to half of its length to stop the fall without injuring the climber.
  54. The hydrogen bonds play a very important part in the structures and properties of biochemical polymers. For example: protein chain often produce a helical structure, and the ability of DNA molecule to replicate themselves depends primarily on the hydrogen bonds, which hold two parts of the molecules in a double helix.
  55. RELATIVE BOND STRENGTH Note that all intermolecular forces are much weaker than the force of attraction found in typical covalent bonds or ionic bond. Instantaneous dipole — induce forces are weaker than dipole — dipole forces. Hydrogen bonds are about twice as strong as the intermolecular forces.
  56. TABLE OF RELATIVE STRENGTH OF INTERMOLECULAR FORCES AND TYPES OF BONDS Instantaneous dipole — induced dipole forces e.g. Xenon Hydrogen bond e.g. in water O —H covalent bond in water Ionic boning e.g. Sodium chloride BONDS ENERGY (kJ/mol) 15 22 464 760
  57. THANK YOU VERY MUCH FOR YOUR COOPERATION WELCOME TO THE NEXT TOPIC: STATE OF MATTER DO NOT FORGET TO DOWNLOAD THE APP AND WRITE YOUR REVIEW FOR ME

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