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Chemical Bonds

Chemical Bonds. Types of Chemical Bond. When atoms combine to achieve more stable structures, three types of bonding are possible Ionic Bond – results when metallic atoms combine with non-metallic atoms to form and ionic lattice

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Chemical Bonds

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  1. Chemical Bonds

  2. Types of Chemical Bond • When atoms combine to achieve more stable structures, three types of bonding are possible • Ionic Bond – results when metallic atoms combine with non-metallic atoms to form and ionic lattice • Metallic Bond – results when metallic atoms combine to form a metallic lattice • Covalent Bond – results when non-metallic atoms combine to form either molecules or covalent lattices.

  3. METALS Metals are… Solid at room temperature, except mercury, which is liquid ! Metals have… very high melting point. Metals are… shiny when they cut. Metals are… good conductors of heat and electricity. Metals are… usually strong & malleable so they can be hammered into shape.

  4. METALS

  5. Metals in columns 1, 2, 3 are electron donors. NonMetals in columns 5, 6, 7 receive Electrons.

  6. METALS

  7. METALS

  8. METALS FerrousNon-FerrousAlloys Containing iron & Do not contain iron. A mixture of almost all are e.g. aluminium, metals, or a magnetic. copper, silver, gold, metal & small e.g. mild-steel, lid, tin etc. amount of cast-iron, tool- other substance Steel etc. Ferrous AlloysNon-Ferrous Alloys e.g. e.g. brass (copper + zinc) stainless steel bronze (copper + tin ) steel + chromium

  9. Metals • The first widely used metal was copper – first mined and used on the island of Cyprus around 5000 years ago • Low melting point • Easily extracted from its ores • Aluminium (most common metal in the earth’s crust) • Difficult and expensive to extract • Now widely used due to technological advances

  10. Properties of Metals The Lattice structure of metals explains their key properties • Lustre –due to mobile electrons within the lattice being able to reflect light causing the metal to shine • Conduction of heat – electrons are able to gain kinetic energy in hotter areas of the metal and are able to quickly transfer it to other parts of the metal lattice because of their freedom of movement. Heat causes the electrons to move faster and the ‘bumping’ of these electrons with each other and the protons transfers the heat.

  11. Properties of Metals • Conduction of electricity – When an electric field is applied to a metal, one end of the metal becomes positive and the other becomes negative. All the electrons experience a force toward the positive end. The movement of electrons is an electric current.

  12. Properties of Metals 4. Malleability an ductility – metals are malleable and ductile, rather than brittle, as a result of the non-directional nature of metallic bonds. The attractive forces exerted by the positive metal ions for the mobile electrons occur in all directions. This means that layers of atoms can move past one another without disrupting the force between the positive ions and the negative sea of electrons. The nature of the metal does not change when the metal becomes thinner.

  13. Properties of Metals • Melting point and hardness – The generally high melting points and hardness of metals indicate that metallic bonding is quite strong. Melting points and hardness increase with an increase in the number of outer shell electrons, since there is a greater attractive force between the cations and the electrons. • Density – most metals have relatively high densities because metallic lattices are close-packed.

  14. Structure of Metals • Metallic atoms have low electronegativities (lose their outer shell electron easily) • Once a metallic atom loses its outer shell electron it becomes a positively charged cation. • Metals occur as crystal lattices – metallic lattice structures made up of an array of cations • The electrons from each metallic atom are found in a common pool and are free to move between all the cations. Delocalised electrons.

  15. Structure of Metals • Electrostatic forces of attraction between the positively charged cations and the negatively charged electrons hold the lattice together. • A metal is therefore a seen as a rigid framework of cations immersed in a ‘sea’ of electrons that serve as the cement holding the three-dimensional cationic network together – Metallic bonding.

  16. Review • Complete the revision questions page 94 (1 - 3) • Complete the revision questions pages 95,96 (4 – 5)

  17. Properties and Uses of Metals • Page 96 – construct a table of the metals listed and their uses and the appropriate properties

  18. Review • Complete the revision questions page 98 (6, 7, and 9)

  19. Metallic Properties – alternative models • The Ball Bearing Model • Briefly summarise this model for explaining metal strength. • Metals with large grains have fewer dislocations and bend easily • Metals with small grains have many dislocations and do not bend easily

  20. METALS METALS & ALLOYS Metals are available in pure or alloy form. Pure Metals such as pure aluminium or pure copper, contain only one type of metal. They are not mixed with any other metal. Alloys are a mixture of two or more pure metals. Alloys tend to have better strength properties than pure metals. Alloys and pure metals often have special physical properties.

  21. Modifying Metals • Work Hardening • Bending or hammering cold metals causes the crystal grains to become smaller – bending is made more difficult, the metal is toughened or work hardened.

  22. Modifying Metals • Modifying using heat (all processes disrupt the metal lattice) • Annealed metals are heated until they are red hot then cooled slowly. Larger crystals form; increased softness; restores ductility • Quenched metals are heated until they are red hot then cooled quickly. Smaller crystals are formed – metal is harder but brittle • Tempered metals are produced when quenched metals are warmed again to a lower temperature and then allowed to cool slowly. Reduces brittleness and retains hardness.

  23. Modifying Metals • Alloying – mixing a metal with other metal or some non-metals, properties are changed. • Substitutional alloy – atoms of the metals used are about the same size and can replace each other in the metal crystals. Eg Ag and Cu to form Sterling Silver (increased hardness) • Interstitial alloy – atoms of the metals differ greatly. The smaller atoms then fit into the spaces between the larger atoms. Eg. Fe and C to form Steel (stronger and more resistant to corrosion)

  24. METALLIC BONDbond found in metals; holds metal atoms together very strongly

  25. Metallic Bond • Formed between atoms of metallic elements • Electron cloud around atoms • Good conductors at all states, lustrous, very high melting points • Examples; Na, Fe, Al, Au, Co

  26. Metallic Bonds: Mellow dogs with plenty of bones to go around.

  27. Ionic Bond, A Sea of Electrons

  28. Metals Form Alloys Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal. Examples are steel, brass, bronze and pewter.

  29. Review • Complete the revision questions page 102 (15 – 18) • Read ‘Titanium Bicycles’ • Complete the revision questions page 104 (19, 20)

  30. Review • Complete the multiple choice questions pages105, 106 • Complete the review questions pages 106, 107 – 1, 6, 7, 10, 11

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