9. Introducing Little Miss “Element” Hi! I am Little Miss “Element” I am PURE SUBSTANCE I cannot be broken down into any simpler substance by means of a chemical reaction* or electricity**! *Chemical process refers to chemical reaction or heat **Electricity refers to electrolysis
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13. These are elements! Atoms of same element copper element sodium element helium element Molecules of same element Hydrogen gas element ozone Cu Na He H O H O O
14. Atoms An element is made of tiny particles called atoms . The atoms of an element is different from that of another element.
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16. What is an atom? Examples of models of atoms: Hydrogen atom Sodium atom Chlorine atom H Na Cl
17. Molecules Very few elements exists as atoms besides elements such as helium and neon. Most elements exist as molecules. For example, hydrogen is H 2 . Ozone is O 3 .
18. Molecules consisting of a few atoms are called polyatomic molecules . Hydrogen (H 2 ) is a diatomic molecule. Ozone (O 3 ) is a triatomic molecule.
22. Chemical Symbols of Elements Chemists use symbols to represent elements. For example, O represents oxygen while Fe represents iron . Element Symbol Element Symbol Calcium Ca Mercury Hg Carbon C Neon Ne Hydrogen H Silicon Si Iron Fe Sodium Na
23. Classification of Elements – Metals and Non-metals There are two major groups of elements – metals and non-metals . Iron is a metal. Oxygen is a non-metal. There are some elements called metalloids which behave like both metals and non-metals. Metals and non-metals are grouped separately on the Periodic Table .
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25. Physical Properties metals and non-metals Metals Non-metals Shiny appearance Dull appearance Solids at r.t.p (except mercury) Gases, liquids or solids at r.t.p (room temp & pressure) Malleable, Ductile , Sonorous Brittle if solid (general) High melting and boiling points Low melting and boiling points Good conductors of heat Poor conductors of heat Good conductors of electricity Poor conductors of electricity (expect carbon and graphite)
27. Introducing Little Miss “Compounds” Harlow! Hehee!!! *giggles* I am also a PURE SUBSTANCE I am made up of a fixed number of two or more elements chemically combined .
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30. So, what is a compound then? Water Ammonia gas Consists of two or more elements And They are chemically combined together! H
31. Compounds Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white.
32. Making compounds from their elements ELEMENTS COMPOUND hydrogen (colourless gas) oxygen (colourless gas) lighted splint heat, light and explosion water (colourless liquid) Example: Making water (picture) Water molecule Oxygen molecule Hydrogen molecule mixture of hydrogen and oxygen water Example: Making water (models) heat, light and explosion
33. Making compounds from their elements Example: Making iron sulphide compound Iron + sulphur iron sulphide elements compound + yellow grey heat heat black
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36. Little Miss “Compound” Property #3 Because of my chemical bonds , I cannot be broken down by physical means. I can only be broken down by chemical reaction or electricity. Electrolysis (breaking down of compound by electricity) 2MgCl(s) Mg(s) +Cl 2 (g) Thermal Decomposition (breaking down of compound by heat) HgO(s) Hg(s) + O 2 (g)
37. How do we name compounds? Rule 1 A compound made up of two elements has a name that ends in -ide . • Sodium chlor ide — made up of the elements sodium and chlorine • Zinc ox ide — made up of the elements zinc and oxygen • Carbon diox ide — made up of the elements carbon and oxygen
38. How do we name compounds? Rule 2 A compound that contains hydroxide ions , OH – (a negatively charged ion made up of oxygen and hydrogen) is named a hydroxide. • Potassium hydroxide — contains potassium ions and hydroxide ions
39. How do we name compounds? Rule 3 A compound that contains a negatively charged polyatomic ion containing oxygen usually has a name ending in –ate . • Copper(II) sulph ate — contains oxygen atoms in the sulphate ion • Sodium nitr ate — contains oxygen atoms in the nitrate ion
40. Fixed Composition of Compounds For example, water ( H 2 O ) is a compound made only by joining together two atoms of hydrogen to one atom of oxygen. That is, the ratio of hydrogen atoms to oxygen atoms in water is always 2 : 1 . A compound is made up of different elements chemically combined in a fixed ratio .
42. How do we write chemical formula? Rule 1 For many compounds that contain both metallic and non-metallic elements, the symbol of the metallic element is written first . • calcium oxide ( Ca O) • sodium chloride ( Na Cl) • magnesium carbonate ( Mg CO 3 )
43. How do we write chemical formula? Rule 2 The number of atoms is written as a subscript, to the right of the atom’s symbol. • water ( H 2 O , not H2O or 2HO) • magnesium carbonate ( MgCO 3 , not MgCO 3 or MgC 3 O)
44. How do we write chemical formula? Rule 3 It is not necessary to write the subscript ‘1’. • water ( H 2 O , not H 2 O 1 ) • calcium oxide ( CaO , not Ca 1 O 1 )
45. How do we write chemical formula? Rule 4 The oxygen atom is usually written at the end of the formula. • water ( H 2 O , not OH 2 ) • carbon dioxide ( CO 2 , not O 2 C) • nitric acid ( HNO 3 , not O 3 NH)
46. How do we calculate the number of atoms in a formula? Pb(NO 3 ) 2 Number of nitrogen (N) atoms = 1 x 2 = 2 Number of lead (Pb) atoms = 1 Number of oxygen (O) atoms = 3 x 2 = 6
47. Compounds can be Decomposed Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition . Mercury(II) oxide Oxygen
51. Introducing Little Mr. “Mixture” Burp!!!! I am messy! I am formed when two or more substances joined together physically ( without chemical bonds ) I have the same properties as all the substances I am his best friend! AIR
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57. A mixture of 2 elements A mixture of two elements, e.g. neon (Ne) and hydrogen (H 2 )
58. A mixture of 1 element and 1 compound A mixture of one element and one compound, e.g. hydrogen (H 2 ) and ammonia (NH 3 )
59. A mixture of 2 compounds A mixture of two compounds, e.g. water vapour (H 2 O) and carbon dioxide (CO 2 )
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61. Can you differentiate? Compound Mixture of element & compound Mixture of 2 elements-Alloy Molecules of an element Mixture of 2 elements
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63. Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Separation Cannot be separated into its constituents by physical methods . Separation can only be done by chemical methods or by electricity. e.g. Water can only be separated into Hydrogen and Oxygen by Electrolysis. Can be easily separated into its constituents by physical methods . e.g. Salt can be obtained from its solution by evaporation. Water can be obtained by simple distillation.
64. Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Composition The composition is fixed. The constituents (elements) in the compound are combined in definite amount. e.g. To form one molecule of water, two atoms of Hydrogen and one atom of Oxygen is needed. Has no fixed composition. The amount of constituents in a mixture can vary. e.g. The amount of salt added into the water to make salt solution can vary and vice versa.
65. Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Properties The physical and chemical properties of the compound is different from the properties of its constituents. e.g. Hydrogen and Oxygen are gases while water is a liquid at room temperature and pressure. e.g. Water has a fixed melting and boiling point. The mixture does not have its own properties. It has the average physical and chemical properties of the constituents that made it up. (Each constituents still retain its own properties) e.g. The salt solution still retains its salt taste. e.g. Salt solution does not have a fixed melting or boiling point, but rather over a range of temperature.
66. Difference between mixtures and compounds. Compounds E.g. Water H 2 O Mixtures E.g. Salt solution Energy Change Energy is usually given out or occasionally taken in when a compound is formed. Normally little or no energy is given out or taken in when a mixture is formed.
67. Differences between mixtures and compounds *giggles* HeE stupid… Laugh what? I know I am a little “bushy and hairy” than you… Little Miss Compound Mr Messy VS
68. Comparison between mixtures and compounds Fixed Variable Mp / Bp Has a fixed composition Does not have a fixed composition Composition A chemical reaction takes place when a compound is formed No chemical change takes place when a mixture in formed Energy Change Properties are unique and different from its elements Same properties as its components Properties (chemical / physical) Elements in a compound Cannot be separated by physical methods Components can be separated by physical methods Separation /breakdown Compound Mixture
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