1. Classification of Matter Elements, Compounds, Mixtures

2. Lesson Objective Physical and Chemical Changes. Elements Compounds Mixtures

3. Physical and Chemical Changes All reaction in Chemistry can be divided into two types of changes: Physical or Chemical. Physical Change: NO new substance is formed. These changes are easily reversible or temporary. An example is dissolving salt in water. Other examples of physical change include: melting, boiling, mixing 2 solids or liquids.

4. Chemical Change: A NEW substance is formed. These changes are irreversible or permanent. The new substance formed will have different properties compared to its original elements. (E.g. different melting and different chemical reactions from the original substance.) Physical and Chemical Changes

5. One can recognize a chemical change from 2 observations: The new substance has a different appearance, such as different color or different physical state. An example is the electrolysis of water. Reason: Electrolysis of water produces two new substances, Hydrogen gas and oxygen gas. Hydrogen and oxygen are both gases but water is a liquid. A lot of heat is given out in a chemical changes. Chemical changes are called chemical reactions. Physical and Chemical Changes

6. Illustration of chemical changes

7. An Overview

8. Elements, Compounds and Mixtures “ single, attached, play play…”

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

10. Elements Definition of an element: An element is a pure substance which cannot be split up into two or more simpler substances by chemical means. Sugar is not an element as it can be broken down into carbon and water.

11. Note that an element: Consists of only one kind of atom, Cannot be broken down into a simpler type of matter by either physical or chemical means Can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen). Elements

12. Examples of elements Elements are made up of tiny particles Elements can be further classified into two groups: Is the smallest particle of an element and has the same chemical properties of the element Is made up of two or more atoms that are chemically bonded together (note: these atoms are of the SAME element!!) Hi, I am from the “Noble gas” family and I work alone We same same!!

13. These are elements! Atoms of same element Cu copper element Na sodium element He helium element Molecules of same element H Hydrogen gas element O H OO ozone

14. Atoms An element is made of tiny particles called atoms. The atoms of an element is different from that of another element.

15. Elements- Atoms Microscopic view of the atoms of the element argon (gas phase). Consists of only one kind of atom

16. What is an atom? Examples of models of atoms: HNaCl Hydrogen atom Sodium atom Chlorine atom

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. Hydrogen (H 2 ) is a diatomic molecule. Ozone (O 3 ) is a triatomic molecule. Molecules consisting of a few atoms are called polyatomic molecules.

19. Elements- Molecules Microscopic view of the molecules of the element nitrogen (gas phase). Consists of only one kind of atom

20. Examples of molecules (elements) HH NN O O O OO S SS S S S S S

21. Allotropes of Carbon molecule (element) Carbon is an element but made up of a very large molecule (also known as MACROMOLECULE) There are 3 types of carbon molecular structures –C 60 –Diamond –Graphite

22. Chemical Symbols of Elements Chemists use symbols to represent elements. For example, O represents oxygen while Fe represents iron. ElementSymbolElementSymbol CalciumCaMercuryHg CarbonCNeonNe HydrogenHSiliconSi IronFeSodiumNa

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.

24. What is an element? An element is a substance that cannot be broken down into two or more simpler substances by any chemical means. - They are arranged in the Periodic Table, classified as metals and non-metals. - They may consist of atoms of same element or molecules of the same element. Metals (excluding hydrogen) Non-metals (including hydrogen)

25. Physical Properties metals and non-metals MetalsNon-metals Shiny appearanceDull appearance Solids at r.t.p (except mercury) Gases, liquids or solids at r.t.p (room temp & pressure) Malleable, Ductile, SonorousBrittle if solid (general) High melting and boiling points Low melting and boiling points Good conductors of heatPoor conductors of heat Good conductors of electricity Poor conductors of electricity (expect carbon and graphite)

26. Summarising Elements Metals Non Metals Atoms Molecules

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.

28. Compounds Note that a compound: can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), has properties that are different from its component elements, and always contains the same ratio of its component atoms.

29. A compound is a substance which is made up of two or more elements chemically combined together. What is a compound? - Chemical reactions taking place. Cu Qn: Is this a compound? It only contains one type of element. Qn: Is this a compound? HH It only contains one type of element. H O H O O Qn: Is this a compound? It is not chemically combined.

30. So, what is a compound then? O HH Water N HHH Ammonia gas Consists of two or more elements And They are chemically combined together!

31. Compounds Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white.

32. ELEMENTS COMPOUND hydrogen (colourless gas) oxygen (colourless gas) lighted splint heat, light and explosion water (colourless liquid) Making compounds from their elements 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 black

34. Little Miss “Compound” Property #1 I can be represented as a “chemical formula” The different elements present in a compound are combined in a fixed ratio General Rules: - Only write the name of the metallic element first - Write the number of atoms of any element in the compound in subscript (applies to only 2 or more atoms) - “ide” will always be written at the end of the non metal element Special Rules: Does not apply to organic compounds (chapter 18 onwards)

35. Little Miss “Compound” Property #2 I am formed by atoms of different elements. However, I do not have the properties as them. Examples Na + Cl 2  NaCl (s) (g) (s) H 2 + O 2  H 2 O (g) (g) (l)

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 chloride — made up of the elements sodium and chlorine Zinc oxide — made up of the elements zinc and oxygen Carbon dioxide — 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) sulphate — contains oxygen atoms in the sulphate ion Sodium nitrate — 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.

41. Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Chemical Formula of a Compound A compound can be represented by a chemical formula. The chemical formula states the types of atoms (i.e. elements) in the compound, the ratio of the different atoms in the compound. Types of atoms: hydrogen, oxygen Ratio of H to O = 2:1

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 (CaO) sodium chloride (NaCl) magnesium carbonate (MgCO 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. Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition. Compounds can be Decomposed Mercury(II) oxide Oxygen

48. Summarizing A compound is made up of two or more elements chemically joined together A compound has a fixed composition Every compound has a unique chemical formula A compound has a completely different properties from its elements A chemical reaction (decomposition or electrolysis) is needed to separate the elements in the compound

49. Molecules- Elements or compounds? A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. It can be a molecule of an element E.g. N 2, O 2, S 8 It can be molecule of a compound. H 2 O, CO 2, NH 3 N N OO S S S S S S S S O H H OO C N H HH

50. Think about this… ROJAK!!

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 AIR I am his best friend!

52. Mixtures Definition of a mixture: A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.

53. Mixtures Note that a mixture: consists of two or more different elements and/or compounds NOT chemically combined. Can be homogeneous or non-homogeneous can be separated into its components by physical means, and often retains many of the properties of its components.

54. Microscopic view of a gaseous mixture containing two elements (argon and nitrogen) and a compound (water). Mixtures

55. Examples of mixtures include muddy water and air. Air is made up of gases such as nitrogen and oxygen mixed together.

56. Little Mr “Mixture” I do not have a fixed composition of the substances. A Mixture can be: element + element element + compound compound + compound (Refer to page 59, Fig 4.7) He is a “boo-boo!” He can be separated to its substances by physical methods

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 )

60. Mr Alloy Alloy: What is it?? It is a mixture of metals with other elements Alloy metals are generally stronger and better in physical properties Examples –Steel (Iron + Carbon) –Stainless Steel (Nickel + Iron + Chromium + carbon) –Brass (Copper + Zinc) Yup! That’s ME!

61. Can you differentiate? Compound Mixture of element & compound Mixture of 2 elements-Alloy Molecules of an element Mixture of 2 elements

62. Conclusion An element is a pure substance which cannot be split up into two or more simpler substances by chemical means. A compound consist of a fixed number of different kinds of atoms chemically combined together. A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.

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 CompoundMr Messy

68. Comparison between mixtures and compounds FixedVariable Mp / Bp Has a fixed compositionDoes not have a fixed composition Compositio n 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 CompoundMixture

69. Challenge Time Is mineral water an element, mixture or compound?

70. Challenge Time Are YOU an element, mixture or compound?

71. EXTRA! Human body is made up of 28 elements? About 99% our mass is made up of the 6 main elements –Oxygen(65%) –Carbon(18%) –Hydrogen (10%) –Nitrogen(3%) –Calcium(1.5%) –Phosphorus (1.5%)

72. The End……