Ch06 elements, compounds & mixtures


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Ch06 elements, compounds & mixtures

  1. 1. Chapter 6: Elements, Compounds and Mixtures
  2. 2. Before we move on, We have… Representing the video clip available
  3. 3. Lesson Outline <ul><li>recognise that substances can be classified as elements, compounds and mixtures </li></ul><ul><li>distinguish among elements, compounds and mixtures </li></ul><ul><li>identify an element as the basic building block of matter </li></ul><ul><li>recognise that elements are classified according to their properties </li></ul><ul><li>describe compounds as substances consisting of two or more chemically combined elements </li></ul><ul><li>describe mixtures as two or more elements and/or compounds that are not chemically combined </li></ul><ul><li>classify elements as metals and non-metals based on their characteristic properties </li></ul><ul><li>show an appreciation of the systematic investigation involved in the study of substance </li></ul>
  4. 4. 6.1 Elements Elements are the simplest kind of matter It cannot be broken down into simpler substances by chemical reactions E.g. When you heat oxygen, expose it to light or pass electricity through it, it does not break down and remains as oxygen. Oxygen + = Oxygen o 2 o 2 lead There are more than 110 elements. Every element is given a name and a chemical symbol. E.g. Helium = He Chemical symbol takes one or two letters from the name of the element First letter is always capitalised and the letter that follows is in lower case For two-letter symbols, they may not always be the first two letters of the name of the element Oxygen o 2
  5. 5. <ul><li>There are some cases where chemical symbols take letters from the name of the element in other languages such as Latin, Greek and Arabic. </li></ul>P lum b um (Latin) Pb Lead H ydrar g yrum (Latinized Greek) Hg Mercury Au rum (Latin) Au Gold S ta n num (Latin) Sn Tin A r g entum (Latin) Ag Silver Cu prum (Latin) Cu Copper Fe rrum (Latin) Fe Iron K alium (Latin) K Potassium Name of element (Language) Chemical symbol Name of element Did You Know ? ? ?
  6. 6. 6.2 Classification of Elements To make the study of matter easier, scientists have classified the elements. Classifying elements according to similar chemical properties arranged systematically in a table is called the Periodic Table . Go to Video 6.1
  7. 7. Classifying Elements by State A simple way to classify elements is to observe their physical states at room temperature. Lead (solid) Mercury (liquid) Chlorine (gas) Classifying Elements as Metals and Non-Metals Here are the characteristic properties that are used to classify elements into metals and non-metals: Metal Non-Metal <ul><li>shiny appearance </li></ul><ul><li>high density </li></ul><ul><li>high melting point </li></ul><ul><li>good electrical and heat conductor </li></ul><ul><li>ductile </li></ul><ul><li>malleable </li></ul><ul><li>sonorous </li></ul><ul><li>dull appearance </li></ul><ul><li>low density </li></ul><ul><li>low melting point </li></ul><ul><li>poor electrical and heat conductor </li></ul><ul><li>non-ductile </li></ul><ul><li>brittle </li></ul><ul><li>non-sonorous </li></ul>
  8. 8. Uses of Metals <ul><li>Aluminium is used to make aircraft bodies, packaging and cooking utensils because it is light and resists corrosion </li></ul><ul><li>Copper does not react to water and is cheap thus it is used to make water pipes to prevent corrosion. It is also used to make wires as it is a good conductor of electricity. </li></ul><ul><li>Silver reflects light so well that it is used to coat glass to make mirrors. Some other uses include jewellery, coins and electrical contacts. </li></ul>Can you think of more uses of metals?
  9. 9. Uses of Non-metals <ul><li>Hydrogen is used </li></ul><ul><li>as rocket fuel </li></ul><ul><li>for making margarine </li></ul><ul><li>for filling weather balloons </li></ul><ul><li>Oxygen is used </li></ul><ul><li>for respiration </li></ul><ul><li>for combustion </li></ul><ul><li>in oxy-acetylene flames for welding </li></ul><ul><li>Carbon is used </li></ul><ul><li>in the formation of living tissues </li></ul><ul><li>as a fuel </li></ul><ul><li>in pencil leads </li></ul>
  10. 10. Sodium chloride (salt) 6.3 Compounds A compound is a substance consisting of two or more different chemically combined elements Compounds are formed during chemical reactions , where heat and sometimes light energy is given out or taken in E.g. H 2 O (chemical formula of water) Type of element: Hydrogen Number of element: 2 Type of element: Oxygen Number of element: 1 A chemical formula is used to describe the number and type of elements that constitute a compound It is a process in which the original substances are changed to one or more new substances. H H O
  11. 11. Formation of Compounds Chemical combination of elements Magnesium and oxygen combine chemically to produce magnesium oxide (compound) Word equation : Magnesium + oxygen magnesium oxide (element) (element) (compound) Chemical combination of elements and compounds When colourless oxygen and nitrogen dioxide is mixed, they combine chemically to produce a coloured compound, nitrogen dioxide Word equation : Nitrogen oxide + oxygen nitrogen dioxide (compound) (element) (compound)
  12. 12. Chemical combination of compounds When colourless gaseous ammonia is mixed with colourless gaseous hydrogen chloride, they combine chemically to produce a white solid, ammonium chloride. Word equation : Ammonia + hydrogen chloride ammonium chloride (compound) (compound) (compound)
  13. 13. 6.4 Some Common Characteristics of Compounds All compounds share some common properties which enable us to identify them. <ul><li>Compounds are formed by chemical reactions, which usually involve an exchange of energy (heat/light) with the surroundings. </li></ul><ul><li>A compound has properties that are different from the properties of its constituent elements </li></ul>Sodium (solid) Chlorine (gas) Sodium chloride (solid) + How is sodium chloride different from sodium or chlorine?
  14. 14. <ul><li>A compound can only be broken down into simpler substances by chemical methods (e.g. thermal decomposition) </li></ul><ul><li>The different elements in a compound are chemically combined in a fixed proportion by mass </li></ul>2g of hydrogen + 4g of oxygen 6g of water boiling to dryness evaporating dish pipe clay triangle tripod stand Bunsen burner
  15. 15. 6.5 Mixtures A mixture is made up of two or more substances not chemically combined. It may consist of elements, compounds or both. It may be made up by solids, liquids or gases. Other examples of mixtures include fog, muddy water, honey, milk, some medicines, brass and steel. Examples of Useful Mixtures: Clean air It is a mixture of gaseous elements (nitrogen, oxygen) and compounds (carbon dioxide) Duralumin It is a mixture of aluminium, copper, magnesium and manganese
  16. 16. 6.6 Some Common Characteristics of Mixtures Mixtures <ul><li>Not formed by chemical reactions (no heat/light energy is given out or taken in) </li></ul><ul><li>has properties of its constituent substance </li></ul><ul><li>Substances can be mixed in any proportion by mass </li></ul><ul><li>It can be separated into its components by physical means (evaporation, filtration, distillation) </li></ul>evaporating dish pipe clay triangle tripod stand Bunsen burner cooling water out cooling water in heat distillate The solution is heated
  17. 17. 6.7 Distinguishing Among Elements, Compounds and Mixtures With the help of classification keys, it is easier to differentiate elements, compounds and mixtures. Some examples of classification keys Branching out every section under elements, compounds and mixtures makes comparing them so much easier, now even I can differentiate them fast! Classification web Classification branch