2. Unit 1 Building Blocks

3. Menu To work through a topic click on the title. Substances Reactions Rates The structure of the atom Bonding structure and properties Chemical symbolism The mole Click here to End.

4. Substances

5. Elements Everything in the world is made from about 100 elements. Each element has a name and a symbol. The symbol is usually one capital letter and one small letter e.g. Ca Chemists have arranged elements in the Periodic Table.

6. The Periodic Table Chemists have arranged elements in the Periodic Table. The vertical columns are called groups. The horizontal rows are called periods. Elements in the same group of the Periodic Table show similar chemical properties.

7. The Periodic Table The elements in group 1 of the Periodic table are called the alkali metals. They are very reactive metals.

8. The Periodic Table The elements in group 7 of the Periodic table are called the halogens. They are reactive non- metals.

9. The Periodic Table The elements in group 0 (8) of the Periodic table are called the noble gases. These are very unreactive gases.

10. The Periodic Table The elements between groups 2 and 3 are the transition metals.

11. Elements Most elements are solid at room temperature. Mercury and bromine are liquid at room temperature. 11 elements – hydrogen, nitrogen, oxygen, fluorine, chlorine, helium, neon, argon, krypton, xenon, radon - are gases at room temperature.

12. Elements Elements can be classified as metals or non-metals. There are more metals than non- metals.

13. Elements Many elements have everyday uses. Aluminium is used as kitchen foil. Carbon is used in pencil leads. Gold, silver and platinum are used in jewellery. Copper is used in electrical wiring.

14. Elements Some elements, including gold, silver and copper, have been known for a long time. The most recently discovered elements have been made by scientists.

15. Compounds Compounds are formed when elements react together.

16. Mixtures Mixtures occur when two or more substances come together without reacting.

17. Compounds Compounds with a name ending in “ –ide “ contain the two elements named. Copper chloride contains copper and chlorine. Sodium oxide contains sodium and oxygen.

18. Compounds Compounds with a name ending in “ -ite “ or “ -ate “ contain the two elements named and the element oxygen. Copper carbonate contains copper, carbon and oxygen. Sodium sulphite contains sodium, sulphur and oxygen.

19. Chemical Reactions When a chemical reaction takes place one or more new substances are made. Burning a match is a chemical reaction because new substances are made. Melting ice is not a chemical reaction since ice is solid water.

20. Chemical Reactions How do we know that a chemical reaction has taken place? There is a change in appearance A precipitate is formed A gas is given off Energy is released or taken in

21. Chemical Reactions In an exothermic reaction energy is released. In an endothermic reaction energy is taken in.

22. Air Air is a mixture of gases. Air is approximately 80% nitrogen and 20% oxygen. The test for oxygen is that it relights a glowing splint. The splint will not relight in air because there is not enough oxygen.

23. Solutions A solution is formed when a substance dissolves in a liquid. A substance which dissolves in a liquid is soluble. A substance which does not dissolve in a liquid is insoluble.

24. Solutions If we only dissolve a small amount of substance we make a dilute solution. If we dissolve a large amount of substance we make a concentrated solution. A solution is diluted by adding more liquid.

25. Solutions A saturated solution is one in which no more substance can be dissolved.

26. Substances Click here to repeat Substances. Click here to return to the Menu Click here to End.

27. Reaction Rates

28. Following the course of a reaction Reactions can be followed by measuring how some quantity we can measure changes with time. Reactions can be followed by measuring changes in concentration, mass or volume of either the reactants or products

29. Following the course of a reaction The average rate of a reaction, or stage in a reaction, can be calculated by dividing the difference between the initial and final quantities by the time interval. Rate =  change  time

30. Following the course of a reaction Volume of gas released (ml) Time (s)

31. Following the course of a reaction Volume of gas released (ml) Time (s) V1V1 t1t1

32. Following the course of a reaction Volume of gas released (ml) Time (s) V1V1 t1t1 V2V2 t2t2

33. Following the course of a reaction Volume of gas released (ml) Time (s) V1V1 t1t1 V2V2 t2t2 Volume change (  V)  V = V 2 – V 1

34. Following the course of a reaction Volume of gas released (ml) Time (s) V1V1 t1t1 V2V2 t2t2 Time change (  t)  t = t 2 – t 1

35. Following the course of a reaction Volume of gas released (ml) Time (s) V1V1 t1t1 V2V2 t2t2 Average reaction rate between t 1 and t 2. Rate =  V/  t

36. Following the course of a reaction The rate of a reaction, or stage in a reaction, is proportional to the reciprocal of the time taken. Rate proportional to 1/t

37. Factors affecting rate The rates of reactions are affected by changes in Concentration Particle size Temperature.

38. Collision Theory Reactions will only take place when the reacting particles collide.

39. Collision Theory Reactions will only take place when the reacting particles collide.

40. Collision Theory The particles need to collide at the correct angle.

41. Collision Theory The particles need to collide at the correct angle.

42. Collision Theory The particles need to collide at the correct angle.

43. Activation energy Two molecules approach each other

44. Activation energy If they don’t have the required activation energy nothing happens.

45. Activation energy Two molecules approach each other

46. Activation energy If they have the required activation energy the molecules form the Activated complex

47. Activation energy If they have the required activation energy the molecules form the Activated complex

48. Activation energy The activated complex splits apart To form the products.

49. Collision Theory Collision theory explains the effect of concentration on reaction rates. The more particles there are in a given volume, the greater the chance of collision.

50. Concentration

51. Collision Theory Collision theory explains the effect surface area on reaction rates. Collisions can only take place on the surface. The larger the surface the more collisions.

52. Surface Area

53. Temperature Each molecule has a kinetic energy. Not all molecules in a material have the same kinetic energy. Temperature is a measure of the average kinetic energy of the molecules.

54. Temperature The higher the temperature the more energy molecules have. Molecules at a higher temperature move more quickly. This means that there are more collisions each second and so a faster reaction.

55. Catalysts Catalysts speed up reactions, without being changed by the reaction. Catalysts are used in many industrial processes. They reduce the temperature needed, so reducing energy costs.

56. Catalysts Heterogeneous catalysts are in a different state from the reactants they catalyse. Homogeneous catalysts are in the same state as the reactants they catalyse.

57. Catalysts Heterogeneous catalysts work by the adsorption of reactant molecules. The adsorption of the molecules loosens bonds and makes it easier for the substance to react.

58. Catalysts The surface activity of a catalyst can be reduced by poisoning, when surface sites are taken over by other substances, preventing reactants being adsorbed. Impurities in the reactants result in the industrial catalysts having to be regenerated or renewed.

59. Catalytic converters Catalytic convertors are fitted to cars to catalyse the conversion of poisonous carbon monoxide and oxides of nitrogen to carbon dioxide and nitrogen.

60. Catalytic converters Cars with catalytic converters only use ‘lead-free’ petrol to prevent poisoning of the catalyst.

61. Enzymes Enzymes catalyse the chemical reactions which take place in the living cells of plants and animals. Enzymes are used in many industrial processes.

62. Enzymes Enzymes are catalysts which affect living things. Enzymes are used to make: Yoghurt Cheese Medicines Beer

63. Reaction Rates Click here to repeat Reaction Rates. Click here to return to the Menu Click here to End.

64. The structure of the atom

65. The Periodic Table The elements are classified by arranging them in the Periodic Table. The atoms in the Periodic Table are listed in order of their Atomic Number.

66. Rutherford’s Atom Elements are made of small particles called atoms In the centre of the atom is the nucleus, containing protons and neutrons. Electrons orbit around the nucleus, like planets around the Sun.

67. Atoms Most of the mass of the atom is found in the nucleus The nucleus contains positively charged protons. The nucleus also contains neutrons, which have no charge. Negatively charged electrons orbit around the nucleus.

68. Atoms For each atom the Atomic Number is equal to the number of protons. The Mass Number is the number of protons + neutrons. The number of neutrons is Mass Number minus Atomic Number.

69. Atoms The atom is neutral because the positive charge of the nucleus is balanced by the negative charge of the electrons. Thus the number of electrons is the same as the number of protons.

70. Representing Atoms We represent atoms using nuclide notation:

71. Electrons The first shell holds 2 electrons.

72. Electrons The first shell holds 2 electrons. The second shell holds 8 electrons

73. Electrons The first shell holds 2 electrons. The second shell holds 8 electron The third shell holds 8 electrons

74. Electrons The number of outer electrons in an atom is the same as the number of its group in the Periodic Table. Atoms with the same number of outer electrons will have similar chemical properties.

75. Electrons Since electrons are impossible to track down can also show them pear-shaped in electron pair clouds Each cloud can hold two electrons

76. Sub-Atomic Particles ParticleChargeMassLocation Protonpositive1 a.m.u.nucleus Neutronnone1 a.m.u.nucleus ElectronnegativenegligibleIn orbit around the nucleus

77. Isotopes Not all atoms of the same element have the same mass. Most elements are mixtures of isotopes. Isotopes are atoms with the same number of protons but different numbers of neutrons.

78. Isotopes Relative Atomic Mass is the average mass number of an atom. It is not whole number because most elements consist of a mixture of isotopes. Different isotopes have different abundances.

79. The Structure of the Atom Click here to repeat The Structure of the Atom. Click here to return to the Menu Click here to End.

80. Bonding, structure and properties

81. Elements and compounds. All the elements in the Periodic Table, except the Noble Gases, form compounds. All the elements in the Periodic Table, except the Noble Gases, do not have completely filled outer electron energy levels.

82. Elements and compounds. When atoms form compounds they do so in order to achieve a completely full outside electron energy level. To do this they must share, gain or lose electrons.

83. Bonds The forces involved in sharing, gaining or losing electrons are called bonds. Bonds are the forces of attraction which hold compounds together. Some of these forces are strong, and some are weak.

84. Bonding The bonds formed when atoms share electrons are called covalent bonds. The bonds formed when atoms gain or lose electrons are called ionic bonds. Metallic bonds are found in metal elements.

85. Covalent bonds Whenever bonds are formed, the atoms must collide with each other. When some atoms collide with each other, the electrons in the outer shell can be shared between the atoms.

86. Covalent bonds When a collision takes place between atoms it must have sufficient energy to form a compound The outer energy levels overlap and the atoms share the electrons.

87. The Covalent Bond As two atoms come together the half-filled electron pair clouds overlap to form a new cloud.

88. The Covalent Bond As two atoms come together the half-filled electron pair clouds overlap to form a new cloud. The covalent bond

89. The Covalent Bond The overlap area has an increase in negative charge, which is strongly attracted by the positive nuclei of both atoms. e-e-e-e- + +

90. Covalent bonds This draws the atoms close together. The force of attraction between the nuclei and the shared electrons forms a strong covalent bond. e-e-e-e- ++

91. Polar covalent bonds Sometimes one atom has a greater force of attraction than the other. This leads to polar covalent bonding, where there are slight charges (shown by  + and  -) on the atoms. e-e-e-e- ++ 

92. The bonds in water are very polar because oxygen attracts electrons more strongly than hydrogen.

93. Ionic Bonds Some substances are made up of ions. Ions can be positively or negatively charged. They are formed when an atom, or group of atoms lose or gain electrons.

94. Examples Na  Na + + e sodium atomsodium ion Cl 2  2Cl - + 2e chlorine moleculechloride ions

95. In ionic bonding, electrons are transferred from one atom to another allowing both atoms to achieve a stable electron arrangement. Ionic bonds are very strong.

96. For example, sodium and chlorine atoms would form an ionic bond making the compound sodium chloride as shown below :

97. Metallic bonds Metals lose their outer shell electrons to gain a stable electron arrangement, forming positive ions. These electrons are delocalised moving freely between these ions.

98. The attraction between the positive ions and delocalised electrons forms a metallic bond which is very strong.

99. Molecules

100. Some substances are made up of discrete molecules. Molecules are made up of two or more atoms held together by strong covalent bonds.

101. Diatomic molecules A diatomic molecule is made up of two atoms. Hydrogen, nitrogen, oxygen, the halogens and carbon monoxide exist as diatomic molecules.

102. Diatomic molecules We can draw diagrams to show the formation of diatomic molecules.

103. Diatomic molecules We can draw diagrams to show the formation of diatomic molecules. + H + H

104. Diatomic molecules We can draw diagrams to show the formation of diatomic molecules. +  H + H  H 2

105. Diatomic molecules We can draw diagrams to show the formation of diatomic molecules.

106. Diatomic molecules We can draw diagrams to show the formation of diatomic molecules. Cl + Cl +

107. Diatomic molecules We can draw diagrams to show the formation of diatomic molecules. Cl + Cl  Cl 2 + 

108. Diatomic molecules Some diatomic molecules involve more than one covalent bond. O2O2 N2N2

109. Covalent molecules We can draw similar diagrams of discrete covalent molecules. ammonia NH 3 methane CH 4

110. Covalent substances The bonds between the molecules are weaker than the covalent bonds within molecules. A covalent network structure consists of a giant lattice of covalently bonded atoms.

111. Formulae of discrete molecules For discrete covalent molecules the chemical formula uses atomic symbols to show the number and type of atom present. For example C 3 H 8 means that the molecule of this compound contains 3 carbon atoms and 8 hydrogen atoms.

112. Other formulae The empirical formula shows the simplest ratio of particles present. For example C 4 H 8 has an empirical formula of CH 2.

113. Other formulae The structural formula shows the relative position of atoms. For example C 4 H 8 (butene)has the following structural formula. H H H H H C C C C H H H

114. We can write formulae by counting the atoms in a model or picture.

119. Formulae of covalent networks Covalent network structures do not contain discrete molecules. Their chemical formulae are empirical formulae, showing the simplest ratio of the types of atom present.

120. SiO 2 means that silicon dioxide contains two oxygen atoms for each silicon atom. SiC means that silicon carbide contains one carbon atom for each silicon atom.

121. Formulae of ionic lattices An ionic structure consists of a giant lattice of oppositely charged ions. The formula for an ionic compound gives the simplest ratio of positive ions to negative ions.

122. NaCl means that sodium chloride contains one sodium ion (Na + ) for each chloride ion (Cl - ).

123. Conductivity An electric current is a flow of electrons. Conductors are materials which allow an electric current to pass through. Insulators are materials which do not allow an electric current to pass through.

124. Conductivity CONDUCTORS Metals Graphite (a form of carbon - the only non-metallic conductor) Solutions of ionic metal compounds Molten ionic compounds

125. Conductivity Electrons move through solids. Metal elements (solids) and carbon (graphite) are conductors of electricity because they contain free (delocalised) electrons. Metals in the liquid state will also conduct for the same reasons.

126. Conductivity Covalent substances (solids, liquids, solutions) do not conduct electricity since they are made up of molecules which are uncharged.

127. Ions and Conductivity Ions move through liquids. Positive ions are formed when atoms lose electrons. Negative ions are formed when at atoms gain electrons.

128. An ionic solution or a melt will conduct because its ions are free to move to the electrode of opposite sign. An ionic solid does not conduct because its ions are unable to move.

129. Liquid or Gas At room temperature A liquid or gaseous compound will be covalent. A liquid or gas contains small discrete molecules between which there are fairly small forces of attraction.

130. Solids At room temperature A solid compound can be ionic or covalent Solids are a result of very strong forces holding the particles together.

131. Types of Solid In an ionic solid these forces are the ionic bonds i.e. the forces of attraction between the oppositely charged ions. These forces are very strong so the melting point of this type of solid is very high.

132. A covalent network solid consists of a huge number of atoms held together by a network of covalent bonds. These covalent bonds are very strong so the melting point of this solid is very high.

133. A covalent molecular solid consists of molecules held together by a network of van der Waals forces. These van der Waals forces are weak so the melting point of this solid is low.

134. Soluble in water? Most ionic substances are soluble in water, the lattice breaking, to free the ions Most covalent substances are insoluble in water but can dissolve in other solvents.

135. Electrolysis Electrolysis occurs when d.c. (direct current) is passed through a melt, or an ionic solution. This changes the compound, releasing new substances at the electrodes.

136. An electrolyte is a substance which conducts when molten or in solution. While most ions are colourless, some are coloured. e.g. cobalt - pink/purple; copper - blue; dichromate - orange; nickel - green; permanganate - purple

137. Electrolysis At the positive electrode: Chlorine, bromine, iodine or oxygen (from water) are released. At the negative electrode: Copper, silver or hydrogen (from water) are released.

138. Electrolysis of copper(II) chloride The negative chloride ion moves to the positive electrode where: 2Cl -  Cl 2 + 2e - l -+ Cl -

139. Electrolysis of copper(II) chloride The positive copper ion moves to the negative electrode where: Cu 2+ + 2e -  Cu l -+ Cu 2+

140. Bonding, Structure and Properties Click here to repeat Bonding, Structure and Properties Click here to return to the Menu Click here to End.

141. Chemical Symbolism

142. Formula A chemical formula shows the relative number of each type of atom present in the compound.

143. The name can tell us how many atoms are there. Mono- means 1 Di- means 2 Tri - means 3 Tetra- means 4 Pent- means 5 Hex- means 6 Hept- means 7 Oct- means 8

144. The name can tell us how many atoms are there.

148. Valency Valency is a number which helps us work out molecular formulae. It is the combining power of the atom. Valency is Group Number 8 minus Group Number

149. Group12345670/8 Valency12343210

150. Chemical Formulae Using valency 1.Write down symbols 2.Write down valencies 3.Swap over 4.Divide (if possible) 5.Formula

151. Using valency carbon and oxygen 1.Write down symbols C O 2.Write down valencies 4 2 3.Swap over 2 4 4.Divide (if possible) 1 2 5.Formula CO 2

152. Using valency calcium and chlorine 1.Write down symbols Ca Cl 2.Write down valencies 2 1 3.Swap over 1 2 4.Divide (if possible) 5.Formula CaCl 2

153. More Valency Valency for ions made from more than one atom are found from the size of charge on ion. Multiple of these ions are written in brackets.

154. More Valency OH - has valency 1 Magnesium hydroxide’s formula is written Mg(OH) 2

155. copper(II) has a valency of 2 copper(I) has a valency of 1 Valency for transition metals (which can have different valencies) are given by the number after metals name

156. Using valency copper(II) nitrate 1.Write down symbols Cu NO 3 2.Write down valencies 2 1 3.Swap over 1 2 4.Divide (if possible) 5.Formula Cu(NO 3 ) 2

157. Chemical Equations Reactants are the materials with which are present at the start of the reaction and are changed by the reaction. Products are the materials produced by the chemical change. These are separated by an arrow (which means “gives”). Reactants  Products

158. Whenever we write a chemical equation we need to know what substances are present at the start what are the new substances formed in the chemical reaction.

159. To know the chemical reactants and products means we can write a word equation Here we are naming the reactants and products. e.g. propane + oxygen  carbon dioxide + water

160. We need to convert the word equation into symbols: C 3 H 8 + O 2  CO 2 + H 2 O If we look closely at this equation we will realise that it is unbalanced – there are different numbers of atoms on each side: 3xC + 8xH + 2xO  C + 2xH + 3xO

161. We must write a balanced chemical equation where there are equal numbers of moles of each type of atom on both sides. We can balance the equation we have been working with.

162. Propane has 3 carbons so: C 3 H 8 + O 2  3CO 2 + H 2 O Propane has 8 hydrogens so: C 3 H 8 + O 2  3CO 2 + 4H 2 O To balance out the oxygens: C 3 H 8 + 5O 2  3CO 2 + 4H 2 O This is a balanced chemical equation.

163. Chemical Symbolism Click here to repeat Chemical Symbolism Click here to return to the Menu Click here to End.

164. The mole

165. Formula Mass Formula mass is found by adding together the relative atomic masses of all the atoms present in the formula, e.g. calcium carbonate CaCO 3 Ca 40 C 12 O 16x3 48 Formula Mass 100

166. The mole A mole is the formula mass in grams. If we look at the previous example 1 mole of calcium carbonate is 100 grams.

167. Moles To connect gram formula mass, mass in grams and number of moles use the triangle opposite gfm = mass of 1 mole n = number of moles m = mass of substance m gfmn

168. Using Chemical Equations The numbers we use to balance an equation are the actual numbers of moles which react. This gives us the mole relationship in the reaction. If we look at the example we have been given: C 3 H 8 + 5 O 2  3CO 2 + 4H 2 O 1 mole + 5 moles  3moles + 4moles

169. Since one mole is the formula weight in grams we can now work out the masses which react. C 3 H 8 + 5 O 2  3CO 2 + 4H 2 O 1 mole 5 moles  3mole 4moles 1x44g 5x32g  3x44g 4x72g 44g 160g  132g 72g Now by proportion we can work out any reacting quantities.

170. Example How much oxygen is needed to burn 0.22g of propane? C 3 H 8 + 5 O 2  3CO 2 + 4H 2 O 1 mole 5 moles 3mole 4moles To burn, 1 mole C 3 H 8 needs 5 moles O 2 44g C 3 H 8 needs 160g O 2 0.22g C 3 H 8 needs 0.8g O 2

171. The Mole Click here to repeat the Mole Click here to return to the Menu Click here to End.

172. The End Hope you found the revision useful. Come back soon!!