C2 REVISION POWERPOINT. Suitable for: Yr 11 Dual award Yr 11 separate Science

Transcription

1 C2 REVISION POWERPOINT Suitable for: Yr 11 Dual award Yr 11 separate Science Revision websites: e

2 C2 REVISION CHECKLIST STRUCTURE AND BONDING C2.1 Structure and Bonding An ion is a charged particle which has either lost of gained electrons Metal atoms lose electrons to become positive ions Non-metals atoms gain electrons to become negative ions Ionic bonds form between metal and non metal atoms Ions have charges relating to the number of electrons lost or gained Ionic bonding is described as the transfer of electrons Ionic bonding can be represented using a dot and cross diagram Examples of ionic compounds include sodium chloride, potassium bromide, magnesium oxide. The ionic formula e.g MgO can be worked out from the charges on the ions The electrostatic attraction between the positive and negative ions s known as the ionic bond Covalent bonds form between non-metal atoms Examples of covalent molecules include water, carbon dioxide, ammonia, methane Covalent bonding can be represented using a dot and cross diagram Ionic substances have high melting points. Ionic substances a hard and brittle Ionic substances are soluble in water Ionic substances conduct electricity when molten or in solution Ionic substances form a giant ionic lattice (crystal structure) Covalent molecules have low boiling points Covalent molecules do not conduct electricity Covalent molecules are normally gases at room temperature

3 C2.1 STRUCTURE AND BONDING C2.1 Structure and Bonding Ionic substances have a high melting point because of the electrostatic attraction (force) between the positive and negative ions. This attraction occurs because opposite charges attract. Ionic substances conduct electricity when molten or in solution because the ions are free to move Covalent molecules are gases at room temperature and have low boiling points due to the weak intermolecular forces between molecules. Covalent molecules do not conduct electricity because they are neutral molecules and have no charge Atoms that share electrons can also form giant structures or macromolecules. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures (lattices) of atoms. All the atoms in these structures are linked to other atoms by strong covalent bonds and so they have very high melting points. Diamond and graphite are giant covalent structures. These giant covalent substances have very high melting points. This is because of the strong covalent bonds, lots of energy is needed to break these bonds. Diamond and graphite are allotropes of carbon. This means they are both made of carbon but have different properties & structure. Graphite is a non metal but can conduct electricity. This is because graphite has free(delocalised electrons) HT Graphite has free electrons because each carbon atom is covalently bonded to 3 others leaving 1 electron free per carbon atom. Graphite has strong covalent bonds and weak intermolecular forces between layers. Graphite is slippery and can rub off in layer this is why it is used in pencil lead In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard.

4 C2.3.1 Atomic structure Atoms can be represented as shown in this example: Mass number 23 Na Atomic number 11 The relative masses of protons, neutrons and electrons are: Name of particle Mass Proton 1 Neutron 1 Electron Very small The total number of protons and neutrons in an atom is called its mass number. Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element. The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element. (HT only) The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. The relative formula mass of a substance, in grams, is known as one mole of that substance.

5 C2.3.2 Analysing substances Elements and compounds can be detected and identified using instrumental methods. Instrumental methods are accurate, sensitive and rapid and are particularly useful when the amount of a sample is very small. Chemical analysis can be used to identify additives in foods. Artificial colours can be detected and identified by paper chromatography. Gas chromatography linked to mass spectroscopy (GC-MS) is an example of an instrumental method: gas chromatography allows the separation of a mixture of compounds the time taken for a substance to travel through the column can be used to help identify the substance the output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column the mass spectrometer can also give the relative molecular mass of each of the substances separated in the column. (HT only)

6 C2.3.3 Calculations The percentage of an element in a compound can be calculated from the relative mass of the element in the formula and the relative formula mass of the compound. The empirical formula of a compound can be calculated from the masses or percentages of the elements in a compound. (HT Only) The masses of reactants and products can be calculated from balanced symbol equations. Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product because: the reaction may not go to completion because it is reversible some of the product may be lost when it is separated from the reaction mixture some of the reactants may react in ways different from the expected reaction. The amount of a product obtained is known as the yield. When compared with the maximum theoretical amount as a percentage, it is called the

7 C2.3.4 Rates of reaction The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time: Rate of reaction = amount of reactant used time Rate of reaction = amount of product formed time Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy. The minimum amount of energy particles must have to react is called the activation energy. Increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically. This increases the rate of reaction. Increasing the pressure of reacting gases increases the frequency of collisions and so increases the rate of reaction. Increasing the concentration of reactants in solutions increases the frequency of collisions and so increases the rate of reaction. Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction. Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts. Catalysts are important in increasing the rates of chemical reactions used in industrial

8 C2.3.5 Exothermic and Endothermic reactions When chemical reactions occur, energy is transferred to or from the surroundings. An exothermic reaction is one that transfers energy to the surroundings. Examples of exothermic reactions include combustion, many oxidation reactions and neutralisation. Everyday uses of exothermic reactions include self-heating cans (eg for coffee) and hand warmers. An endothermic reaction is one that takes in energy from the surroundings. Endothermic reactions include thermal decompositions. Some sports injury packs are based upon endothermic reactions. If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case.

9 C2.6 Acids, Bases and Salts The ph scale goes from 0 to 14, and ph 7 is a neutral solution. Acid + Alkali Salt + water (Neutralisation reaction) Acid + Base Salt + water (Neutralisation reaction) Acid + Metal Salt + Hydrogen Metal oxides and hydroxides are bases. Soluble hydroxides are called alkalis. The particular salt produced in any reaction between an acid and a base or alkali depends on: the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates) the metal in the base or alkali. Hydrogen ions, H+(aq), make solutions acidic and hydroxide ions, OH (aq), make solutions alkaline. The ph scale is a measure of the acidity or alkalinity of a solution. In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation: H+(aq) + OH (aq) H2O(l)

10 C2.3.7 Electrolysis When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution. Passing an electric current through ionic substances that are molten, for example lead bromide, or in solution breaks them down into elements. This process is called electrolysis and the substance that is broken down is called the electrolyte. During electrolysis, positively charged ions move to the negative electrode, and negatively charged ions move to the positive electrode. Electrolysis is used to electroplate objects. This maybe for a variety of reasons and includes copper plating and silver plating. At the negative electrode, positively charged ions gain electrons (reduction) and at the positive electrode, negatively charged ions lose electrons (oxidation). If there is a mixture of ions, the products formed depend on the reactivity of the elements involved. Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite. Aluminium forms at the negative electrode and oxygen at the positive electrode. The positive electrode is made of carbon, which reacts with the oxygen to produce carbon dioxide. The electrolysis of sodium chloride solution produces hydrogen and

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12 PURE substances have different STRUCTURES depending on the type of BONDING they have IONIC eg sodium chloride (salt) SIMPLE MOLECULAR eg carbon dioxide, water COVALENT GIANT MOLECULAR eg diamond, graphite METALLIC eg copper The structure of a substance decides what its PHYSICAL PROPERTIES will be.

13 IONIC C Ionic substances are compounds of metals and non-metals (eg sodium chloride, copper oxide, magnesium sulphide etc) They are made of IONS: atoms which have lost or gained electrons giving them a positive or negative CHARGE Positive sodium ion Na + Negative chloride ion Cl - The + ions and ions STRONGLY ATTRACT each other to make a regular crystal structure

14 Because of the very STRONG BONDS between the IONS, ionic compounds have HIGH MELTING & BOILING POINTS Strong ionic bond Sodium chloride melts at over 800 C

15 Ionic compound Melting point ( C) Iron chloride 677 Potassium chloride 770 Sodium chloride 801 Copper oxide 1446 Calcium oxide 2707

16 As ionic compounds are made of CHARGED IONS, they can CONDUCT ELECTRICITY but ONLY if the ions can MOVE. If it is MOLTEN the ions can move MEL T If it is DISSOLVED the ions can move + DISSOLV E C 20 C H 2 O

17 + MOLTEN IONIC COMPOUND MOLTEN ionic compounds CONDUCT ELECTRICITY

18 When salt is put in water, H 2 O molecules pull the ions apart to make a solution. This lets the ions move around. H 2 0 molecule Ions free to move around

19 PURE WATER SOLID SALT SALT SOLUTION DISSOLVED ionic compounds also CONDUCT ELECTRICITY

20 SIMPLE MOLECULAR SUBSTANCES These are substances like carbon dioxide CO 2, water H 2 O and methane CH 4 which are always made of simple molecules whether they are SOLIDS, LIQUIDS OR GASES H atom O atom Whole thing = H 2 O molecule

21 MOLECULES ONLY WEAKLY ATTRACT EACH OTHER VERY STRONG bonds BETWEEN ATOMS (so molecule is very hard to break up) WEAK bonds BETWEEN MOLECULES (so molecules are easy to separate)

22 SOLI D LIQUI D GAS Simple molecular substances can only be a liquid or a solid when the temperature is LOW enough for the WEAK BONDS to pull the molecules together

23 This means simple molecular substances have LOW melting and boiling points Compound Mpt ( C) Bpt ( C) State at room temp Water H 2 O Liquid Butane C 4 H Gas Methane CH Gas Carbon dioxide CO Gas Oxygen O Gas Hydrogen H Gas Solid oxygen at C Liquid oxygen boiling at C

24 As the bonds between the molecules are weak, simple molecular substances are weak and soft when solid. As the molecules are NOT CHARGED simple molecular substances DON T CONDUCT ELECTRICITY when solids, liquids or gases.

25 GIANT MOLECULAR SUBSTANCES In these materials strong covalent bonds join atoms together with other atoms of the same type to make giant structures, rather than little groups. DIAMON D Carbon atom Every C atom joined to 4 others Only STRONG bonds (this is only part of the structure - the same pattern carries on in every direction)

26 SILICA (Silicon dioxide SiO 2 ) has a similar structure to diamond Every Si atom joined to 4 O atoms Silica is the main substance in ROCKS. Pure silica is called QUARTZ

27 Because all the atoms in Giant Structures are joined by STRONG BONDS they: Have HIGH melting / boiling points Are usually HARD and STRONG Because all the atoms in Giant Structures are UNCHARGED, they will not conduct electricity.

28 GRAPHITE a special case Common form of carbon found in soot, charcoal, pencil leads etc Carbon atoms each joined to 3 others with STRONG bonds to make hexagonal sheets of atoms WEAK BONDS STRONG BONDS The sheets of atoms are joined to other sheets by WEAK bonds

29 As the C atoms are only bonded to 3 others, the extra electrons form clouds of free electrons between the layers As the bonds between the layers of atoms are weak, they can easily slide over each other

30 GRAPHITE - Properties The STRONG BONDS between the ATOMS mean it has HIGH MELTING and BOILING POINTS The WEAK BONDS between the LAYERS mean it is SOFT and SLIPPERY as the layers SLIDE over each other easily (used in pencils and as a solid lubricant) The FREE ELECTRONS between the layers mean that graphite CONDUCTS ELECTRICITY (used as sliding contacts in electric motors)

31 METAL S In a metal the atoms are held together by strong bonds in regular structures. This means most metals have high melting and boiling points and are hard and strong

32 In a metal the atoms LOSE SEVERAL OF THEIR OUTER ELECTRONS which drift around between the metal ions as FREE ELECTRONS. As they have LOST a few electrons, the atoms become POSITIVE IONS HIGHER TIER ONLY Free ( delocalised ) electrons

33 The large number of free electrons makes all metals are GOOD CONDUCTORS of electricity AND heat. The regular structure means the layers of atoms can fairly easily slide over each other without breaking the bonds (though not as easily as graphite) and so metals are MALLEABLE (bend rather than snap) HIGHER TIER ONLY

34 SUMMARY - IONS IONIC Descriptions ONLY Crystals Dissolve in water eg sodium chloride (salt) IONS + FREE ELECTRON S METALLIC Strong malleable solids Don t dissolve eg copper SIMPLE MOLECULAR Usually Gases eg CO 2, H 2 O MOLECULE S ONLY ATOMS joined into GIANT MOLECUL ES GIANT MOLECULAR Hard strong solids Don t dissolve eg diamond (graphite special case)

35 Structure Property SUMMARY - PROPERTIES Reason Ionic Covalent Simple molecular Covalent giant molecular Covalent - graphite Metallic HIGH mpt/bpt CONDUCT: Solid NO Molten YES Dissolved YES LOW mpt/ bpt (often gas at room temp). Soft when solid CONDUCT: Never HIGH mpt/bpt. Hard & strong CONDUCT: Never HIGH mpt/bpt Soft & slippery CONDUCT: YES (fairly well) HIGH mpt/bpt. Hard & strong Malleable CONDUCT: YES (very well) Strong bonds between IONS Ions can t move Ions can move to carry current Bonds between MOLECULES very weak. Molecules aren t charged Strong bonds between all ATOMS No free charges/electrons Strong bonds between ATOMS Weak bonds between LAYERS Free electrons between layers Strong bonds between IONS Regular structure, layers slide Free electrons between ions

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37 KEY WORDS Describe the following keywords to each other. Atom Ion Ionic compound Electron Attraction Free ions

38 Electrolysis is splitting up substances using electricity (Lysis is latin for splitting)

39 WHAT IS ELECTROLYSIS? Electric current is used to breakdown a substance made up of ions ( ionic compounds) An electrolyte is the name for the substance being broken down

40 ELECTROLYSIS OF AN IONIC SOLUTION - YOUTUBE An ionic compound can be split back into its elements through electrolysis. E.g NaCl Sodium chloride (An ionic compound can be turned back into its atoms sodium and chlorine.)

41 Positive Anode Don t get stressed in the exam: Remember PANIC Negativ e Is Cathode

42 ELECTROLYSIS OF MOLTEN NACL ANODE The metal goes to the cathode and the non metal goes to the anode. - CATHODE Cl - Na + Na + Na + Cl - Na + Cl - Cl -

43 positive electrode (anode) + - negative electrode (cathode) Zn + Zn + Cl - Zn + Zn + molten zinc chloride (ions free to move) Cl - Zn + Cl - Cl - Zn + Cl - Zn + Cl - Cl - Zn + Cl -

44 The + - positively charged zinc ions are attracted to the negative electrode Cl - Zn + Cl - Zn + Cl - Cl - Zn + Cl - Zn + Zn +

45 Cl negatively Cl - The charged chloride ions are attracted to the positive electrode Cl - Zn Zn + + Zn + Zn + Zn + Cl - Cl -

46 Compound Anode Cathode Sodium Bromide Potassium Iodide Calcium Fluoride Magnesium Oxide Lithium Chloride

47 Electrolysis of lead bromide = bromide ion = lead ion Cathode Anode

48 = bromide ion = lead ion At the cathode: Pb + gains electrons to form lead metal. It is REDUCED. Anode Cathode At the anode: Br - loses electrons to form bromine gas. It is OXIDISED.

49 O.I.L.R.I.G. Oxidation is loss of electrons Reduction is gain of electrons

50 Cathode Negative Anode Positive Positive ions attracted Negative ions attracted REDUCTION happens here ( positive ions gain electrons) OXIDATION happens here (negative ions lose electrons

51 What happens when the ionic compounds are dissolved in water? Here, water molecules break up into HYDROGEN IONS, H + and HYDROXIDE IONS OH - H 2 O H + + OH - So, in an ionic solution (eg sodium chloride solution), there will be FOUR types of ion present: TWO from the ionic compound and TWO from the water (H + + OH - ) SODIUM CHLORIDE SOLUTION NaCl (aq) H + Cl - OH - H + Na + Na + OH - Na + H + Cl - OH - Cl -

52 IONIC SOLUTION H + Cl - OH - H + Na + OH - OH - Na + H + Cl - Na + Cl - Which ions gain or lose electrons ( get discharged ) and which stay in solution?

53 IONIC SOLUTIONS: At the CATHODE Na + sodium ION, missing 1 electron + H + hydrogen ION, missing 1 electron H Hydrogen ATOM, NEUTRAL which ions? As HYDROGEN is LESS REACTIVE than SODIUM, it is discharged. The sodium ions stay in solution. At CATHODE: 2H + + 2e - H 2 Na + H + H H + Na +

54 IONIC SOLUTIONS: At the CATHODE halogen compounds hydroxide chloride ION, Cl O H ION, from chlorine ATOM, - extra 1 Cl water extra NEUTRAL electron electron + H H O Cl Cl - Cl Cl - O Cl - Cl - O H O H If the ion is a HALOGEN (Cl, Br, I) it is discharged and chlorine (or Br or I) is given off and the OH - ions stay in solution which ions? At ANODE: 2Cl - 2e - + Cl 2

55 IONIC SOLUTIONS: CATHODE non halogen compounds NO 3 - nitrate ION, extra 1 electron O H hydroxide ION, OH - from water, extra electron + O Oxygen atom NO - 3 H O NO - 3 H O NO - 3 O H NO - 3 O H If the ion is NOT a halogen (eg nitrate, sulphate etc) then the HYDROXIDE ions from the water are discharged to make WATER and OXYGEN gas. The other ions stay in solution. which ions? At CATHODE: 4OH - 2H 2 O + O 2 + 4e -

56 RULES FOR IONIC SOLUTIONS + ANODE - CATHODE Attracts ions ( Anions ) Attracts + ions ( Cations ) If ions are HALOGENS ie chloride Cl - bromide Br - iodide I - the HALOGEN is produced. If ions are NOT HALOGENS Eg sulphate SO 4 2-, nitrate NO 3- carbonate CO 3 2- OXYGEN is produced. If + ions (metals) are MORE REACTIVE than hydrogen K, Na, Ca, Mg, Zn, Fe Then HYDROGEN is produced If + ions (metals) are LESS REACTIVE than hydrogen Cu, Ag, Au Then the METAL is produced

57 (REACTIVITY: K + Na + Ca 2+ Mg 2+ Al 3+ Zn 2+ Fe 3+ H + Cu 2+ Ag + Au 3+ ) Compound State Ions Cathode (-) Anode (+) potassium chlorine potassium chloride molten K + Cl - aluminium oxide molten Al 3 + O 2 - aluminium oxygen copper chloride solutio n Cu 2 + Cl - H + OH - copper chlorine sodium bromide solution Na + Br - H + OH - hydrogen bromine silver nitrate solution Ag + NO 3 - H + OH - silver oxygen potassium chloride solution K + Cl - H + OH - hydrogen chlorine zinc sulphate solution Zn + SO 4 2- H + OH - hydrogen oxygen (REACTIVITY: K + Na + Ca 2+ Mg 2+ Al 3+ Zn 2+ Fe 3+ H + Cu 2+ Ag + Au 3+ )

58 ELECTROLYSIS makes a CIRCUIT Complete electric circuit: Current carried by: ELECTRONS in electrodes/wires IONS in the electrolyte To DOUBLE the MASS of substance discharged at electrodes: 2 x CURRENT (2x batt. voltage) 2 x TIME current flows for (Q = I t)

59 OILRIG Cl - Cl - Cl - Cl - - ions LOSING electrons to become atoms is called OXIDATION (even though oxygen may not be involved) Oxidation is loss, reduction is gain OILRIG Na + Na + Na + Na + + ions GAINING electrons to become atoms is called REDUCTION

60 INDUSTRIAL USES OF ELECTROLYSIS 1. To extract reactive metals such as ALUMINIUM, sodium, magnesium etc from their compounds. This is EXPENSIVE due to the large amounts of electrical energy needed. Aluminium is extracted from bauxite (Al 2 O 3 ). 2. Electrolysis of BRINE (salt solution) to produce see below CHLORINE (for disinfectants and plastics) HYDROGEN (for ammonia fertilisers, margarine) SODIUM HYDROXIDE (for soap and cleaning agents) 3. Purifying copper. The copper for wiring etc needs to be more pure than that produced in a blast furnace. Electrolysis is used to convert impure copper to pure copper see below

61 INDUSTRIAL ELECTROLYSIS OF BRINE Chlorine Hydrogen gas gas BRINE (NaCl solution) ANODE OH - and Cl - 2Cl - 2e - + Cl 2 CATHODE H + and Na + 2H + + 2e - H 2 OH - left in solution so concentration grows Sodium chloride solution (neutral) slowly changed to sodium hydroxide solution (alkaline) Na + left in solution so concentration grows

62 Industrial chlorine production from electrolysis of brine

63 Mass number Number of protons and neutrons Atomic number Number of protons Atomic Structure Cl Atoms of the same element can have different numbers of neutrons - these atoms are called isotopes of that element. Proton Neutron Electron Relative mass 1 1 negligible Charge location nucleus nucleus shells The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element. The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. The relative formula mass of a substance, in grams, is known as one mole of that substance Same atomic number Different mass number

64 10 Questions Using the following information about Cl and Mg answer the question below 1. What is the mass number of this chlorine atom? 2. What is the atomic number of this chlorine atom? 3. How many protons neutrons and electrons does this chlorine atom have? 4. What is the electron configuration of a chlorine atom? 5. What is the relative mass of an electron? 6. What is the charge on a neutron particle? 7. Where in the atomic structure are electrons located? 8. What is the relative atomic mass of chlorine? 9. Using 35 Cl and 37 Cl as examples explain what is meant by an isotope. 10. What is the relative formula mass (Mr) of MgCl 2? Atomic Structure 35 Cl 17 Mg 24 12

65 Ionic bonding Metal and non-metal electron transfer Metals lose electrons and become positive ions. Non-metals gain electrons and become negative ions. Metals in group 1 form ions with a +1 charge Metals in group 2 form ions with a +2 charge Non-metals in group 6 form ions with -2 charge Non-metals in group 7 form ions with -1 charge sodium chloride magnesium oxide calcium chloride Writing formulae The charges on the positive and negative ions need to balance out Na + Cl - NaCl Mg 2+ O 2- MgO Ca 2+ Cl - Cl - CaCl 2 Properties of ionic compounds Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces in all directions between oppositely charged ions. These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds. When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and carry the current

66 10 Questions 1. Do ionic bonds transfer or share electrons? 2. Ionic bonds exist between.. (a) Metals and Non-metals, (b) Non metals and Non-metals (c) Metals and Metals 3. Elements in group 7 form ions with what charge? 4. Elements in group 3 form ions with what charge? 5. Ionic compounds are held together by strong forces in all directions between oppositely charged ions. 6. Under what 2 conditions will ionic compounds conduct electricity? 7. Draw a diagram to show the electron arrangement in a fluorine ion. 8. Draw a diagram to show the electron arrangement in a magnesium ion. 9. What is the electron configuration of a fluorine ion? 10. What is the formula of calcium fluoride? Ionic bonding E _ C

67 Covalent bonding - molecules Hydrogen - H 2 (g) Chlorine - Cl 2 (g) Hydrogen chloride HCl (g) Water H 2 O (l) Oxygen - O 2 (g) Methane CH 4 (g) Ammonia NH 3 (g) Properties of covalent compounds A covalent bond is a shared pair of electrons Substances that consist of simple molecules are gases, liquids or solids that have relatively low melting points and boiling points They have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils. Intermolecular forces are much weaker than covalent bonds. The forces within the molecules (the covalent bonds) can be referred to as intramolecular forces. They do not conduct electricity because the molecules do not have an overall electric charge. No free electrons or ions.

68 10 Questions 1. Do covalent bonds transfer or share electrons? 2. covalent bonds exist between.. (a) Metals and Non-metals, (b) Non metals and Non-metals (c) Metals and Metals 3. Elements in group 7 form covalent compounds with how many bonds? 4. Elements in group form covalent compounds with 3 bonds? 5. Why do covalent compounds NOT conduct electricity? 6. Are covalent bonds strong or weak? 7. Draw a diagram to show the electron arrangement in a carbon atom. 8. Draw a dot-cross diagram to show the bonding between 2 fluorine atoms 9. Draw a dot-cross diagram to show the bonding present in CH 4? 10. How many bonds does carbon form in CO 2? Covalent bonding - molecules

69 Covalent bonding - Giant Diamond (carbon only) All the atoms in these structures are linked to other atoms by strong covalent bonds and so they have very high melting points. Fullerenes (carbon only) Carbon can also form fullerenes with different numbers of carbon atoms. They are used for drug delivery into the body, lubricants, catalysts, and in nanotubes for reinforcing materials, eg tennis rackets. In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard. Silicon dioxide (Si + O) Sand In graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery. Graphite (carbon only) Giant covalent structures are also called macromolecules. In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity.

70 10 Questions 1. How many bonds do carbon atoms form in diamond? 2. How many bonds do carbon atoms form in graphite? 3. Why is graphite soft and slippery? 4. Why can graphite conduct electricity? 5. What can diamond not conduct electricity? 6. What is the chemical name for sand? 7. Giant covalent structures are also called? 8. Do giant covalent structures have high or low melting points? 9. Explain your answer to question 8. HT only 10. Give a use for fullerenes. Covalent bonding - Giant

71 Metallic bonding Positive ions in a sea of delocalised electrons Metals Metals consist of giant structures of atoms arranged in a regular pattern. The electrons in the highest occupied energy levels (outer shell) of metal atoms are delocalised and so free to move through the whole structure. a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions. Metals conduct heat and electricity because of the delocalised electrons in their structures. The layers of atoms in metals are able to slide over each other and so metals can be bent and shaped. Alloys Alloys are usually made from two or more different metals. The different sized atoms of the metals distort the layers in the structure, making it more difficult for them to slide over each other and so make alloys harder than pure metals. Conduction depends on the ability of electrons to move throughout the metal. Different sized atoms do not form a regular pattern. force heat Shape memory Alloys can return to their original shape after being deformed, eg Nitinol used in dental braces.

72 10 Questions 1. What type of bonding do metals have? 2. Draw a diagram to show the arrangement of atoms in a metal. 3. Do metals have a regular or irregular structure? 4. What is the main purpose of alloying metals? 5. What are alloys called that can return to their original shape? 6. How can we return them to their original shape? 7. What happens to valence (outer) electrons in a metal? 8. What forces of attraction hold metal atoms together? 9. Why can metals conduct electricity? 10. Draw a diagram to show the bonding present in solid sodium. Metallic bonding

73 Polymers and Nanoscience High density polymer chains close together Low density polymer - chains far apart Some do not melt when heated, these are called thermosetting polymers. These cross-links make the material tougher and less flexible. Some will soften easily, and can be moulded into shape before they are cooled down, these are called thermosoftening polymers. The melting point of a thermosoftening polymer is determined by the strength of the INTERMOLECULAR FORCES Nanoscience is the science of very small particles and looks at the properties of nanoparticles. These are particles with in the range of 0 1nm to 100nm. The name 'nano' means A nanoparticle is about 100 atoms Advantages Large surface area makes them effective catalysts. Nanotubes can be used in small scale circuits as nanowires. Disadvantages So small they can enter the skin and therefore the bloodstream. Easily become airborne, breathing in can potentially damage the lungs. Nanoparticles are present in sun screens May be used to develop faster computers, lighter construction materials and new coatings

74 10 Questions 1. Are hydrocarbons tightly packed together in HD or LD polystyrene? 2. Some plastics melt when heated, what do we call them? 3. Some plastics do not melt when heated, what do we call them? 4. Why do they not melt? 5. What is the melting point of a thermosoftening plastic determined by? 6. When we grind solids up into small particles, what happens to the surface area of the solid? 7. What is nanoscience? 8. Approximately how many atoms are in a nanoparticle? 9. State one advantage and one disadvantage of nanoparticles? 10. State one use for nanoparticles. Polymers and Nanoscience

75 Relative abundance Analytical techniques Elements and compounds can be detected and identified using instrumental methods. GC, GC-MS Advantages Highly accurate and sensitive. They are quicker. Enable very small samples to be analysed Chemical analysis can be used to identify additives in foods. Artificial colours can be detected/identified by paper chromatography Disadvantages Equipment is very expensive. Takes specialist training to use. results can ONLY be analysed by comparison with known data A B C D Components in a mixture can be identified by the distance they move relative to the solvent. This is the R f value: Distance moved by component Distance moved by solvent Retention time Different substances, carried by a gas, travel through a column packed with a solid material at different speeds, so that they become separated the number of peaks on the output of a gas chromatograph shows the number of compounds present. The position of the peaks on the output indicates the retention time. The output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column by relative molecular mass The molecular mass is given by the molecular ion peak.

76 1. How can you separate a) A solid from a liquid b) A liquid from a gas c) A liquid from a liquid 2. What is an E-number? 10 Questions 3. State one advantage and one disadvantage of chromatography. 4. What do we call the filter paper after the chromatography experiment has ended? 5. What colours are present in blank inks? 6. What does the R f value represent? 7. What do the initials GC-MS stand for? 8. Give an example of a typical carrier gas in a GC-MS. 9. What is the period of time a gas remains in the column of a GC-MS called? 10. Give a use for chromatography. Analytical techniques

77 Calculations and moles The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12 C isotope. It is an average value for the isotopes of the element The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. The relative formula mass of a substance, in grams, is known as one mole of that substance. Percentage of element in a compound Yield The amount of a product obtained is known as the yield. When compared with the maximum theoretical amount as a percentage, it is called the percentage yield. Reacting masses - What mass of calcium oxide will I get when 20 g of limestone is decomposed? CaCO 3 CaO + CO (3x16) (2x16) 100g 56g 44g As 20g is less than 100g the reaction needs to be scaled down by a factor of: So, mass of CaO = 56x0.20 = 11.2g 20 = Empirical formula is the simplest ratio of atoms in a compound. Molecular formula is the actual ratio of atoms. e.g. What is the empirical formula of a compound containing 40.0% sulfur and 60.0% oxygen by mass? 1. Divide through by Ar 40 : Get molar ratio 1.25 : Get simplest whole number ratio by dividing through by the smallest 1.25 : = 1 : 3 SO 3

78 10 Questions 1. What is the definition for the relative formula mass of a compound? 2. What is the Ar of Cl? 3. What is the Mr of Na 2 O? 4. What is the percentage of Na in Na 2 O? 5. What is the Mr of (NH 4 ) 2 SO 4? 6. What is the percentage of O in (NH 4 ) 2 SO 4? 7. What is the yield of a substance? 8. What mass of magnesium oxide will I get when 42 g of magnesium carbonate is decomposed? 9. Only 18g of magnesium oxide was formed, what is the yield? 10. A hydrocarbon contains 75% carbon and 25% hydrogen by mass, what is the empirical formula? Calculations and moles

79 Reaction kinetics For a reaction to occur: Step 1: Energy must be SUPPLIED to break bonds. Step 2: Energy is RELEASED when new bonds are made. A reaction is EXOTHERMIC if more energy is RELEASED then SUPPLIED (hotter). If more energy is SUPPLIED then is RELEASED then the reaction is ENDOTHERMIC (older). Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product because: the reaction may not go to completion because it is reversible. some of the product may be lost when it is separated from the reaction mixture some of the reactants may react in ways different from the expected reaction. In some chemical reactions, the products of the reaction can react to produce the original reactants. Such reactions are called reversible reactions and are represented: A + B C + ammonium chloride NH 4 Cl (s) CuSO 4.5H 2 O (s) ammonia D NH 3 (g) + HCl (g) If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case. + hydrogen chloride The change from blue hydrated copper sulphate to white anhydrous copper sulphate is one of the most commonly known reversible reactions. hydrated copper sulphate anhydrous + steam copper sulphate CuSO 4 (s) + 5H 2 O (l)

80 10 Questions 1. For a reaction to occur why is energy supplied? 2. Why is energy released during a reaction? 3. If more energy is supplied than released is the reaction exothermic or endothermic? 4. If a reaction is endothermic will the surroundings get warmer or colder? 5. A reaction requires a lot of heat to take place, it is endothermic or exothermic? 6. Is breaking bonds an endothermic or exothermic process? 7. Give 2 reasons why a yield is not always 100%? 8. What is the symbol for a reversible reaction? 9. Give an example of a reversible reaction. 10. If a reversible reaction is exothermic in 1 direction what must it be in the other? Reaction kinetics

81 Reaction rates Amount of product formed Slower rate of reaction here due to reactants being used up Reactions occur when particles collide with sufficient energy. The minimum amount of energy required for particles to react on collision is called the activation energy. Fast rate of reaction here Slower reaction Time Reaction can be followed by: Loss in mass if gas produced. Measuring volume of a gas produced every min. Appearance/disappearance of colour. Change in ph etc. Factors affecting reaction rate Concentration: Increasing concentration increases number of collisions and increases rate Temperature: Particles have more energy and move faster and collide more often. More particles have energy greater than the activation energy so more successful collisions Catalyst: Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts. Catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs. Pressure: Increasing pressure increases the number of collisions as the particles are closer. Surface area: Increases the number of collisions as there is more surface exposed

82 10 Questions 1. What equipment can be used to measure the mass of a product? 2. In terms of reactants how do we know when a reaction is completed? 3. State 2 ways in which a reaction can be followed. 4. Define activation energy. 5. How do catalysts effect the activation energy? 6. How does this change the rate of a reaction? Describe how the following factors effect the rate of a reaction in terms of amount (frequency) of collisions and energy of collisions? 7. Increasing the temperature. 8. Decreasing the concentration. 9. Increasing the pressure of gaseous reactants. 10. Grinding up solid calcium carbonate into a powder. Reaction rates

83 Acids and Bases Acid Formula Salts hydrochloric HCl chlorides sulphuric H 2 SO 4 sulphates nitric HNO 3 nitrates Red Green Purple Increasingly acidic Increasingly basic Acids give H + in water Bases accept H + Alkalis are soluble bases and give OH - in water Bases include, metal oxides, metal hydroxides, metal carbonates Common Acids hydrochloric acid - HCl sulphuric acid - H 2 SO 4 Common Bases sodium hydroxide - NaOH potassium hydroxide - KOH nitric acid - HNO 3 ammonia NH 3 Reactions occur when particles collide with sufficient energy. The minimum amount of energy required for particles to react on collision is called the activation energy. acid acid + + metal base salt salt + + hydrogen water acid + carbonate salt + H 2 O + CO 2 Neutralisation An acid can be neutralised by a base H + (aq) + OH - (aq) H 2 O (l) Base Acid Salt Calcium hydroxide Magnesium oxide Calcium carbonate Hydrochloric acid Nitric acid Sulphuric acid Calcium chloride Magnesium nitrate Calcium sulphate

84 10 Questions 1. What scale is used to measure how acidic or alkaline a substance is? 2. What in the name and formula of the acid that can be used to make magnesium chloride from magnesium ribbon? 3. What is the definition of an acid? 4. What is the difference between an alkali and a base? 5. What gas is formed when an acid reacts with a metal? 6. How can we test for this gas? 7. What is the name of the salt formed when Na 2 O reacts with HNO 3? Balance and complete the following reactions: 1. Mg (s) + HCl (aq) MgCl 2 (aq) + H 2 (g) 2. Al 2 O 3 (s) + HCl (aq) AlCl 3 (aq) + H 2 O (l) 3. Na 2 O (s) + H 2 SO 4 (aq) Acids and Bases

85 Salts Soluble salts Metal can be reacted with an acid until the metal is used up. Excess metal can be filtered off. Water can be evaporated from the solution and the salt left to crystallise Disadvantage: not all metals are suitable; some are too reactive and others are not reactive enough. acid acid + + metal base salt salt hydrogen acid + carbonate salt + H 2 O + CO 2 acid + alkali salt Ammonia dissolves in water to produce an alkaline solution. It is used to produce ammonium salts. Ammonium salts are important as fertilisers water water Place a known volume of alkali in a beaker Add an indicator Add acid dropwise until the solution is neutral. Record the amount of acid required. Mix the same volume of alkali and acid, evaporate off some of the water and leave to crystallise Insoluble salts Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed. The precipitate can be separated using filter paper, washed with distilled water and left to dry. All nitrates are soluble, all sodium salts are soluble. Precipitation can be used to remove unwanted ions from solutions, for example in treating water for drinking or in treating effluent.

86 10 Questions Nickel sulphate (a soluble salt) can be made by adding an excess of insoluble nickel oxide to sulphuric acid until no further reaction occurs. 1. Give an observation that would show you that the reaction is complete? 2. What equipment could be used to removed the excess nickel oxide? 3. What is the name of this separation method? 4. How you could produce crystals of nickel sulphate from nickel sulphate solution? 5. What other reactant could be added to H 2 SO 4 to make nickel sulphate? 6. What is the formula of nickel (II) sulphate? Silver chloride is an insoluble salt which is formed as a precipitate when silver nitrate and sodium chloride solutions are mixed together. 7. Write a word equation for this reaction. 8. What is the formula of silver (I) chloride? 9. After mixing the reactants how could the insoluble salt be separated? 10. Lead nitrate and sodium sulphate are reacted together in solution. Name the two salts made in this reaction? Salts

87 Electrolysis Molten When ionic compounds are melted or dissolved in water the ions can move. Br Positive ions (CATIONS) move to the negative electrode (CATHODE). This means that molten ionic compounds and solutions of ionic compounds conduct electricity. Anode Cathode Br - Br - Pb 2+ Negative ions (ANIONS) move to the positive electrode (ANODE). The solution or melt that is electrolysed is called the ELECTROLYTE. Electrolysis of molten compounds All ionic compounds contain positive and negative ions. We can predict the ions present from the formula and the charges on the ions using the formula and the data sheet. During electrolysis: The CATIONS move to the negative electrode where they GAIN electrons The ANIONS move to the positive electrode where they LOSE electrons OF ELECTRONS e.g. lead bromide PbBr 2 Pb Br - Pb 2+ ions move to the cathode and gain electrons: Pb e - Pb Br - ions move to the anode and lose electrons: 2Br - Br 2 + 2e - O xidation I s L oss R eduction I s G ain

88 10 Questions 1. Why can t ionic solids conduct electricity? 2. What is the name given to the positive electrode? 3. What is a compound split up into using electrolysis? 4. What is the solution or melt that is electrolysed called? 5. What does the acronym O I L R I G stand for? 6. Br - ions reach the positive electrode and loose electrons to form bromine gas, is this process oxidation or reduction? 7. What ions are present in calcium iodide and which electrode would each ion go to? 1. Ca 2+ + e - Ca 2. Cl - Cl 2 + e - Balance and complete the following reactions: 3. CaCl 2 Ca 2+ + Cl - Electrolysis Molten

89 Electrolysis - Solutions At the negative electrode, positively charged ions gain electrons (reduction) and at the positive electrode, negatively charged ions lose electrons (oxidation). If there is a mixture of ions, the products formed depend on the reactivity of the elements involved. Brine Compounds: sodium chloride (NaCl) and water (H 2 O) Ions: Na + + Cl - (Anode) --- OH - + H + (Cathode) Positive electrode 2Cl - Cl 2 + 2e - Negative electrode 2H + + 2e - H 2 When the chloride ions and hydrogen ions have been discharged NaOH is left behind Products in the electrolysis of brine: Chlorine (Cl 2 ) - used in bleach and plastics. Hydrogen (H 2 ) - used in the hydrogenation of vegetable oil to make butter. Sodium hydroxide (NaOH) - used in soap. Electroplating Electrolysis is used to electroplate objects. This may be for a variety of reasons and includes copper plating and silver plating. Passing a current through a solution containing Cu2+ ions or Ag+ ions will result in the silver or copper being deposited on the cathode. Extraction of aluminium Bauxite aluminium ore containing aluminium oxide Aluminium oxide has a very high melting point The electrolysis takes place when the aluminium oxide is molten. It is dissolved in molten cryolite to reduce the temperature at which it melts. This reduces energy costs The cathode and anode are made of graphite Negative electrode 3Al + + 3e - Al Positive electrode 2O 2- O 2 + 4e - Oxygen is released at the anode where it reacts with the graphite to form carbon dioxide. Therefore the anode needs to be replaced often

90 Electrolysis - Solutions 1. What is the chemical formula of salt in the sea? 2. What ions are present in brine? 3. What are the 3 products made when brine undergoes electrolysis? Give a use of each one. 4. What ions move towards the anode? 5. What ions move towards the cathode? 6. What gas discharged at the anode (write the ionic equation as well)? 7. What gas discharged at the cathode (write the ionic equation as well)? 8. What ions are left in solution? 9. What is the name of the compound left in the solution 10. When bauxite undergoes electrolysis what metal is formed and why does the carbon anode need to be frequently replaced? Electrolysis Molten

91 Mark Scheme Atomic Structure protons, 18 neutrons, 17 electrons 4. 2,8, shells (or) orbitals Isotopes - Atoms of the same element that have different numbers of neutrons 35 Cl 18 neutrons 37 Cl 20 neutrons Ionic bonding 1. Transfer 2. (a) Metals and Non-metals Electrostatic 6. Molten (l) or in solution (aq) MgCl 2 = (1xMg) + (2xCl) = (1x24) + (2x35.5) = = [2,8] CaF 2

92 Mark Scheme Covalent bonding - molecules 1. Share 2. (b) Non metals and Non-metals They do not conduct electricity because the molecules do not have an overall electric charge. (or) No free electrons or ions. 6. Strong Covalent bonding - Giant In graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery. 4. In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity. 5. No delocalised electrons. 6. Silicon dioxide 7. Macromolecules 8. High 9. Giant covalent structures are linked by strong covalent bonds and so they have very high melting points. 10. They are used for drug delivery into the body, lubricants and catalysts.

93 Mark Scheme Metallic bonding 1. Metallic Regular 2. To make them harder 3. Shape memory alloys 4. Heat them up 5. The outer electrons of metal atoms are delocalised and so free to move through the whole structure. 6. Strong electrostatic attractions. 7. Metals conduct heat and electricity because of the delocalised electrons. 8. Positive ions in a sea of delocalised electrons Polymers and Nanoscience 1. High Density (HD) 2. Thermosoftening 3. Thermosetting 4. Cross-links in the structure 5. The melting point of a thermosoftening polymer is determined by the strength of the INTERMOLECULAR FORCES 6. Gets bigger 7. Nanoscience is the science of very small particles and looks at the properties of nanoparticles. 8. A nanoparticle is about 100 atoms 9. Advantages: Large surface area makes them effective catalysts. Nanotubes can be used in small scale circuits as nanowires. Disadvantages: So small they can enter the skin and therefore the bloodstream. Easily become airborne, breathing in can potentially damage the lungs. 10. Sun screens (or) Bandages - others

94 Mark Scheme Analytical techniques 1. (a) Filtering (b) take the lid off (c) chromatography 2. Codes for chemicals which can be used as food additives for use within the EU. 3. Advantages: Highly accurate and sensitive. They are quicker. Enable very small samples to be analysed Disadvantages: Equipment is very expensive. Takes specialist training to use. results can ONLY be analysed by comparison with known data. 4. Chromatogram 5. All colours 6. Distance compound travels up chromatogram 7. Gas Chromatography Mass Spectrometry 8. He (or) N 2 (or) H 2 9. Retention time 10. Separating a mixture of liquids (or) Money and cheques can be proven as fakes using this scientific technique - others Calculations and moles 1. The relative formula mass of a substance, in grams, is known as one mole of that substance Na 2 O = (2xNa) + (1xO) = (2x23) + (1x16) = = % of Na = ( 46 / 62 ) x 100 = 74.2% 5. Mr of (NH 4 ) 2 SO 4 = % of O = ( 64 / 132 ) x 100 = 48.5% 7. The amount of a product obtained is known as the yield. 8. MgCO 3 MgO + CO 2 ( ) (24+16) 84g 40g 42g 20g 9. Yield = ( 18 / 20 ) x 100 = 90% 10. C H 75 / / CH 4