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C07 chemical bonding
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  • 1. Chapter 7 Chemical Bonding LEARNING OUTCOMES       Explain the formation of ionic bonds; Define and give examples of ionic solids; Explain the formation of covalent bonds; Define and give examples of simple molecular solids; Explain metallic bonding; Relate the structure of sodium chloride to its properties; 1
  • 2. Chapter 7 Chemical Bonding LEARNING OUTCOMES     Distinguish between ionic and simple molecular solids; Explain the term allotropy; Define and give examples of giant molecular solids; Relate the structure of diamond and graphite to their properties 2
  • 3. Chapter 7 Chemical Bonding The Electronic Structure of Noble Gases The noble gases like helium, neon and argon, which are in Group 0 of the Periodic Table, are very unreactive.  They do not form bonds with other atoms.  They have fully filled outermost (valence) shells.  Except for helium, which has 2 outer electrons, all the other noble gases have 8 outer electrons.  3
  • 4. Chapter 7 Chemical Bonding The Electronic Structure of Noble Gases    The outer shell of 8 electrons is called an octet structure and it makes the atom very stable. E.g. Helium, neon, argon Atoms of other elements become stable like the noble gases by losing or gaining electrons or by sharing electrons. They achieve this by forming bonds with other atoms. 4
  • 5. Chapter 7 Chemical Bonding Types of Bonds Covalent Bond Sharing of Electrons Between Non-metals Ionic Bond Transfer of Electrons Between Metal + Non-metal 5
  • 6. Chapter 7 Chemical Bonding Ionic Bonds  When sodium reacts with chlorine, the sodium atom loses an electron to become a positively charged sodium ion: 6
  • 7. Chapter 7 Chemical Bonding Ionic Bonds  The chlorine atom gains an electron to become a negatively charged chloride ion: 7
  • 8. Chapter 7 Chemical Bonding Ionic Bonds  The positive sodium ion and the negative chloride ion then attract each other to form sodium chloride.  Sodium chloride is called an ionic compound. 8
  • 9. Chapter 7 Chemical Bonding Other ionic compounds   Another example of an ionic compound is that formed between magnesium and chlorine. Each magnesium atom transfers 2 electrons, one to each chlorine atom, to form magnesium chloride. The formula of magnesium chloride is therefore 9 given as MgCl2.
  • 10. Chapter 7 Chemical Bonding Quick check 1 1. Ionic bonds are formed between a ______ and a _____. 2. A metal atom ______ an electron to form a _______ ion while a non-metal ______ an electron to become a ________ ion. 3. The two oppositely charged ions ________ each other to form an ______ compound. 4. An ionic bond is formed by the _________ of _______. 5. (a) Is aluminium oxide an ionic or covalent compound? (b) State the formula of aluminium oxide. 10 Solution
  • 11. Chapter 7 Chemical Bonding Solution to Quick check 1 1. Ionic bonds are formed between a metal and a non-metal. 2. A metal atom loses an electron to form a positive ion while a non-metal gains an electron to become a negative ion. 3. The two oppositely charged ions attract each other to form an ionic compound. 4. Ionic bond is formed by the transfer of electrons. 5. (a) Aluminium oxide is an ionic compound. (b) Al2O3 11 Return
  • 12. Chapter 7 Chemical Bonding Covalent Bonds  A hydrogen atom has only one electron in its first shell. To achieve a more stable structure like helium, it needs one more electron in the first shell.  So two hydrogen atoms join together and share their electrons. A hydrogen molecule is formed.  12
  • 13. Chapter 7 Chemical Bonding Covalent Bonds   This sharing of electrons is called covalent bonding. In an oxygen atom, the outer shell has 6 electrons, so to achieve an octet structure of 8 electrons like neon, two oxygen atoms combine to share 4 electrons. This is called a double bond. 13
  • 14. Chapter 7 Chemical Bonding Other covalent molecules Methane H Water H C H H O H H CH4 (4 single bonds) H2O (2 single bonds) 14
  • 15. Chapter 7 Chemical Bonding Quick Check 2 1. The joining of atoms to form a molecule is called __________ ________ . 2. The two types of bonds are ________ bond and ________ bond. 3. Covalent bonds are formed by the _________ of _________ . 4. Ionic bonds are formed by the __________ of_________ . 5. _________ ______ are formed between non-metals e.g. hydrogen, oxygen and carbon. 15 Solution
  • 16. Chapter 7 Chemical Bonding Lesson 2 Solution to Quick check 2 1. The joining of atoms to form a molecule is called chemical bonding . 2. The two types of bonds are covalent bond and ionic bond. 3. Covalent bonds are formed by the sharing of electrons . 4. Ionic bonds are formed by the transfer of electrons . 5. Covalent bonds are formed between non- metals e.g. hydrogen, oxygen and carbon. 16 Return
  • 17. Chapter 7 Chemical Bonding Properties of Covalent Compounds  The intermolecular forces between the molecules are weak so covalent compounds have low melting and boiling points. For example, water, a covalent compound, has a melting point of 0 oC and a boiling point of 100 oC. Weak intermolecular forces 17
  • 18. Chapter 7 Chemical Bonding Properties of Covalent Compounds Covalent compounds do not conduct electricity in any state.  Most covalent compounds are insoluble in water. Instead they are soluble in organic solvents. For e.g. iodine is insoluble in water, but soluble in ethanol.  water Pure water does not conduct electricity 18
  • 19. Chapter 7 Chemical Bonding Properties of Ionic Compounds  The electrostatic forces between the oppositelycharged ions are very strong so ionic compounds have very high melting points and boiling points. For e.g. sodium chloride, an ionic compound, has a melting point of 801 oC and a boiling point of 1 517oC. 19
  • 20. Chapter 7 Chemical Bonding Properties of Ionic Compounds  Ionic compounds conduct electricity when molten or dissolved in water. This is because the ions can move about and conduct electricity.  Most ionic compounds are soluble in water, but insoluble in organic solvents. For e.g. sodium chloride is soluble in water, but insoluble in oil or petrol. Molten sodium chloride conducts electricity. 20
  • 21. Chapter 7 Chemical Bonding Summary Differences between Ionic and Covalent Compounds Ionic Compounds Covalent Compounds Have very high melting and boiling points Have low melting and boiling points Conduct electricity when molten or in aqueous solution Cannot conduct electricity in any state Are usually soluble in water, but insoluble in organic solvents Are usually insoluble in water, but soluble in organic solvents 21
  • 22. Chapter 7 Chemical Bonding Quick check 3 1. Covalent compounds have _______ forces of attraction between the molecules, so they have ____ melting points and ______ boiling points. 2. Ionic compounds have very ______ forces of attraction between the oppositely charged ions, so they have very ______ melting points and ______ boiling points. 3. All covalent compounds cannot _____ _______ . 4. All ionic compounds can conduct ________ when they are _______ or ________ in water. 5. Sugar is a covalent compound but it is soluble in water. State one test you would use to show that sugar is a covalent compound. 22 Contd.
  • 23. Chapter 7 Chemical Bonding Quick check 3 (cont.) 6. The table below shows 3 substances. Substance Electrical Conductivity when solid when molten A does not conduct does not conduct B does not conduct conducts C conducts conducts (a) Which substance is an ionic compound? (b) Which substance is a metal? (c) Which substance could be a covalent compound? 23 Solution
  • 24. Chapter 7 Chemical Bonding To learn more about Chemical Bonding, click on the links below! 1. http://www.quia.com/jq/19617.html 2. http://www.purchon.com/chemistry/bonding.htm 24
  • 25. Chapter 7 Chemical Bonding Solution to Quick check 3 1. Covalent compounds have weak forces of attraction between the molecules, so they have low melting points and low boiling points. 2. Ionic compounds have very strong forces of attraction between the oppositely charged ions, so they have very high melting points and high boiling points. 3. All covalent compounds cannot conduct electricity. 4. All ionic compounds can conduct electricity when they are molten or dissolved in water. 5. Dissolve some sugar in water, then try to pass electricity through it. The sugar solution will not able to conduct electricity. Contd. 25
  • 26. Chapter 7 Chemical Bonding Solution to Quick check 3 (contd.) 6. The table below shows 3 substances. Substance Electrical Conductivity when solid when molten A does not conduct does not conduct B does not conduct conducts C conducts conducts (a) Ionic compound: B (b) Metal: C (c) Covalent compound: A 26 Return
  • 27. Chapter 7 Macromolecular Structures Simple molecules  Many covalent substances like water, methane, carbon dioxide and iodine exist as small molecules.  These compounds are said to have simple molecular structures. 27
  • 28. Chapter 7 Macromolecular Structures Macromolecules  Some covalent substances like silicon dioxide (SiO2), diamond and graphite are made up of very large molecules.  These substances are said to have macromolecular structures. 28
  • 29. Chapter 7 Macromolecular Structures Properties of Macromolecules Due to the large structures of these macromolecules, their chemical and physical properties are different from those of the simple molecules.  The macromolecules are solids with very high melting and boiling points. E.g. The melting point of diamond is 3550 oC, compared to 0 oC for water.  Due to their sizes, they are also not as reactive compared to the simple molecules.  29
  • 30. Chapter 7 Macromolecular Structures Metallic bonding Metals are also made up of very large lattice structures.  The metallic structure consists of a lattice of positive ions in a “sea of electrons”.  Metals are malleable because the layers of atoms can slide over one another easily as they are being arranged in neat layers.  30
  • 31. Chapter 7 Macromolecular Structures Properties of Metallic structure     The closely packed positively charged metallic ions form a lattice structure with the outer electrons moving freely around the whole metallic structure. The electrostatic attraction between the metallic ions and the electrons holds the metallic ions tightly in the lattice and this gives the metal a high melting point. The free electrons are able to move and conduct electricity and heat. This explains why metals are good conductors of heat and electricity. 31
  • 32. Chapter 7 Macromolecular Structures Van der Waals Forces -Van der Waals forces of attraction can exist between atoms and molecules. -They are not the same as ionic or covalent bonds. They arise because of fluctuating polarities of nearby particles. -The shape and size of molecules affect the strength of the van der Waals forces. The larger the force, the higher the melting and boiling point. 32
  • 33. Chapter 7 Macromolecular Structures Structure of diamond  In diamond, each carbon atom is linked to four other carbon atoms by strong covalent bonds.  The carbon atoms are arranged in a tetrahedral structure which extends throughout the whole diamond lattice made up of millions of atoms.  Structure of diamond The diamond structure is very rigid and the bonds are very strong and difficult to break. This explains why diamond is very hard and strong and has a very high melting point (3550 ºC) and very high boiling point (4827 ºC). 33
  • 34. Chapter 7 Macromolecular Structures Structure of graphite    In graphite, each carbon atom is linked to three other carbon atoms in the same plane by strong covalent bonds. The carbon atoms form six-member hexagonal rings that link up to form flat layers. The hexagonal rings are arranged in parallel layers with weak forces of attraction between the atoms in each layer. 34
  • 35. Chapter 7 Macromolecular Structures Properties of graphite    The covalent bonds between the atoms in each layer are strong, and a lot of heat energy is required to break these bonds when graphite melts. This explains why graphite has a very weak forces high melting point (3652 oC ). Not all the electrons in graphite are used in bonding. There are some free electrons which enable graphite to conduct electricity. The forces of attraction between the atoms in each layer is weak. The layers can easily slide away from each other when a force is applied. For this reason, graphite is smooth and slippery. strong covalent bonds 35
  • 36. Chapter 7 Macromolecular Structures Summary of properties Property Diamond Graphite Hardness and Texture Very hard and strong Soft, smooth and slippery Melting point and Boiling point Very high Very high Electrical Conductivity Does not conduct electricity Conducts electricity 36
  • 37. Chapter 7 Macromolecular Structures Uses of diamond    Due to their differences in properties, diamond and graphite are used in different ways. Diamond being hard and strong, is used for making cutting and drilling tools. Another use for diamond is for making jewellery. jewellery 37
  • 38. Chapter 7 Macromolecular Structures Uses of graphite Graphite being smooth and slippery, is used in making lubricants for use in machinery, motorcar engines and even bicycle chains.  Graphite being chemically unreactive and a conductor of electricity, is used in making electrodes for use in electrolysis and in dry cells.  Due to its very high melting point, graphite is used as a heat insulator. It is used to coat the nose of a insulator space shuttle.  38
  • 39. Chapter 6 Macromolecular Structures Quick check 4 1.The table below shows the properties of 4 substances. Element Conducts electricity in Melting point (OC) Solid state Liquid state W good good 1085 X poor good 801 Y poor poor 3550 Z poor poor 114 Deduce the type of bonds that each substance has. 39 Solution
  • 40. Chapter 6 Macromolecular Structures Quick check 4 (cont’d) 2.The pictures below show 4 types of molecular structures. A B C D Identify the substance or the type of bonds shown by each structure. 40 Solution
  • 41. Chapter 7 Macromolecular Structures Solution to Quick check 4 1. W: metallic bonding, X: ionic bonding, Y: macromolecular (diamond), Z: simple molecular 2. A: graphite; macromolecular B: silicon dioxide; macromolecular C: metallic bonding D: ionic crystal lattice Return 41
  • 42. Chapter 7 Macromolecular Structures To learn more about Macromolecular Structures, click on the links below! • http://mineral.galleries.com/minerals/elements/graphite/graphite.htm • http://www.chemguide.co.uk/atoms/bonding/metallic.html 42