Chemistry_Grade_10-12 (1).pdf

76 chapter 4 atomic combinations figure 411 positive

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CHAPTER 4. ATOMIC COMBINATIONS - GRADE 11 4.8 + + + + + + + + + + + + + + + + + + + + + + + + + + + Figure 4.11: Positive atomic nuclei (+) surrounded by delocalised electrons ( ) 4.8.2 The properties of metals Metals have several unique properties as a result of this arrangement: Thermal conductors Metals are good conductors of heat and are therefore used in cooking utensils such as pots and pans. Because the electrons are loosely bound and are able to move, they can transport heat energy from one part of the material to another. Electrical conductors Metals are good conductors of electricity, and are therefore used in electrical conducting wires. The loosely bound electrons are able to move easily and to transfer charge from one part of the material to another. Shiny metallic lustre Metals have a characteristic shiny appearance and are often used to make jewellery. The loosely bound electrons are able to absorb and reflect light at all frequencies, making metals look polished and shiny. Malleable and ductile This means that they can be bent into shape without breaking (malleable) and can be stretched into thin wires (ductile) such as copper, which can then be used to conduct electricity. Because the bonds are not fixed in a particular direction, atoms can slide easily over one another, making metals easy to shape, mould or draw into threads. Melting point Metals usually have a high melting point and can therefore be used to make cooking pots and other equipment that needs to become very hot, without being damaged. The high melting point is due to the high strength of metallic bonds. Density Metals have a high density because their atoms are packed closely together. Exercise: Chemical bonding 1. Give two examples of everyday objects that contain.. (a) covalent bonds (b) ionic bonds 77
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4.9 CHAPTER 4. ATOMIC COMBINATIONS - GRADE 11 (c) metallic bonds 2. Complete the table which compares the different types of bonding: Covalent Ionic Metallic Types of atoms involved Nature of bond between atoms Melting Point (high/low) Conducts electricity? (yes/no) Other properties 3. Complete the table below by identifying the type of bond (covalent, ionic or metallic) in each of the compounds: Molecular formula Type of bond H 2 SO 4 FeS NaI MgCl 2 Zn 4. Which of these substances will conduct electricity most effectively? Give a reason for your answer. 5. Use your knowledge of the different types of bonding to explain the following statements: (a) Swimming during an electric thunderstorm (i.e. where there is lightning) can be very dangerous. (b) Most jewellery items are made from metals. (c) Plastics are good insulators. 4.9 Writing chemical formulae 4.9.1 The formulae of covalent compounds To work out the formulae of covalent compounds, we need to use the valency of the atoms in the compound. This is because the valency tells us how many bonds each atom can form. This in turn can help to work out how many atoms of each element are in the compound, and therefore what its formula is. The following are some examples where this information is used to write the chemical formula of a compound.
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