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8.1INVESTIGATING ELECTRICAL CONDUCTIVITY OF COMPOUNDS All pure metals conduct an electric current. With the exception of carbon (in the form of graphite),

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Presentation on theme: "8.1INVESTIGATING ELECTRICAL CONDUCTIVITY OF COMPOUNDS All pure metals conduct an electric current. With the exception of carbon (in the form of graphite),"— Presentation transcript:

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3 8.1INVESTIGATING ELECTRICAL CONDUCTIVITY OF COMPOUNDS All pure metals conduct an electric current. With the exception of carbon (in the form of graphite), all pure non-metals do not conduct electricity.

4 Figure 8.1 Investigating the electrical conductivity of compounds. 6 V battery + _ light bulb crocodile clip solid piece under test (a) (b) _ + crucible liquid(molten)/ aqueous under test carbon (graphite) rods

5 chlorine, carbon, hydrogen 1,1,1-trichloroethanesodium, hydrogen, oxygen Sodium hydroxide chlorine, carbonTetrachloromethanepotassium, manganese, oxygen Potassium permanganate carbon, hydrogenHexanecopper, sulphur, oxygen Copper(II) sulphate carbon, hydrogen, oxygen Ethanol (an alcohol)magnesium, sulphur, oxygen Magnesium sulphate hydrogen, oxygenDistilled watercalcium, nitrogen, oxygen Calcium nitrate carbon, hydrogenPolythene (a plastic)potassium, iodinePotassium iodide carbon, hydrogen, oxygen Sugarlead, bromineLead(II) bromide carbon, hydrogenWaxsodium, chlorineSodium chloride Constituent elements (Non-conductors whether solid, liquid or in aqueous solution) Constituent elements (Non-conductors when solid, but conductors when molten or in aqueous solution) Table 8.1 Electrical conductivity and constituent elements of some compounds.

6 ELECTROLYTES are compounds which allow electricity to pass through them only when molten or in aqueous solution. Ionic compounds

7 MetalsMetals Non-metalsNon-metals 1 Compounds solid state molten or aqueous solution (conduct electricity) (do not conduct electricity) Electrolyte

8 Compounds 2 (do not conduct electricity) solid, liquid or in aqueous solution Non-metalsNon-metals Non-metalsNon-metals Non-Electrolyte

9 Why ionic compound is an electrolyte ? How do ionic compound conduct electricity in molten or aqueous state?

10 Solid lead(II) bromide Molten lead(II) bromide does not conduct electricity conducts electricity

11 heat molten lead(II) bromide positive electrode (anode) crocodile clip clamp boiling tube negative electrode (cathode) Glass tubing (connected to a rubber tubing which leads to the fume cupboard) light bulb 6 V battery + _

12 Thus electric current is carried through molten lead(II) bromide by mobile (freely moving) ions.

13 Reddish brown bromine vapour is liberated At positive electrode (anode) (anode) At negative electrode (cathode) (cathode) A silvery grey substance (lead) is deposited

14 ELECTROLYTES AND IONS Electrolytes ELECTROLYTES are compounds which allow electricity to pass through them only when molten or in aqueous solution. There is chemical decomposition during the conduction. ELECTROLYTES are compounds which allow electricity to pass through them only when molten or in aqueous solution.

15 Molten lead(II) bromide is thus decomposed to the two elements lead and bromine. The whole process is called electrolysis (meaning 'decomposition by electricity').

16 Lead(II) bromide does not conduct electricity in solid state. This is because ions in solids are not mobile (i.e. unable to move freely). Pb 2+ Br -

17 Conclusions Ionic compounds in molten or aqueous states can conduct electricity. It is because there are mobile ions. Ionic compounds in solid state cannot conduct electricity. It is because ions are not mobile. Electrolytes are compounds which allow electricity to pass through them only when molten or in aqueous solution. There is chemical decomposition during the conduction. Electrolysis means 'decomposition by electricity'. You do not need to remember the observations in electrolysis.

18 ELECTROLYSIS OF AQUEOUS COPPER(II) CHLORIDE SOLUTION Aqueous copper(II) chloride conducts electricity. During electrolysis, copper(II) chloride is decomposed to form copper (reddish brown solid) at cathode and chlorine gas (with smell of swimming pool) at anode.

19 Electrolysis of aqueous copper(II) chloride solution.

20 Q8.2 (a)What charged particles does copper(II) chloride consist of? (b)Explain why solid copper(II) chloride does not conduct electricity, but its aqueous solution does.

21 A8.2 (a)Positively charged copper(II) ions and negatively charged chloride ions. (b)Solid copper(II) chloride consists of ions which are not mobile, therefore it does not conduct electricity. In aqueous solution, the ions become mobile and thus the solution conducts electricity.

22 Q8.3 Which of the following are electrolytes? Wax, sodium chloride, sodium, mercury, ethanol, potassium iodide, sugar, carbon monoxide Sodium chloride and potassium iodide only. A8.3

23 An ION is an atom or a group of atoms having an overall electric charge. A simple (monoatomic) ion is derived from a single atom. A polyatomic ion is derived from a group of atoms.

24 There are two kinds of ions: positively charged ions (cations) and negatively charged ions (anions). Cations and anions cationscations are attracted towards anionsanions cathode anode

25 MIGRATION OF IONS We can observe the migration (movement) of coloured ions during electrolysis.

26 Figure 8.7 To show the migration of coloured ions during electrolysis (using a U- tube). carbon cathode carbon anode dilute hydrochloric acid this region slowly becomes blue due to the migration of positive copper(II) ions towards the negative cathode dilute hydrochloric acid this region slowly becomes orange due to the migration of negative dichromate ions towards the positive anode a gel containing copper(II) ions and dichromate ions + _ + _ 20V d.c. supply

27 To show the migration of purple permanganate ions during under the influence of an electric field(using a strip of filter paper on a microscope slide).

28 Q8.6 Refer to again. (a)Towards which electrode are potassium ions migrating? Why? (b)Can we see the movement of potassium ions? Why? (c)If a chromium(III) sulphate crystal was used instead of a potassium permanganate crystal, what would be observed? Why? Figure 8.8

29 A8.6 (a)The cathode. Potassium ions are positively charged. They are thus attracted towards the negative electrode (cathode). (b) No. Potassium ions are colourless. (c) A green patch would move towards the negative electrode (cathode). Chromium(III) ions are green in colour and positively charged. They are attracted towards the negative electrode.

30 Objectives To define what is chemical bondingTo define what is chemical bonding To define what is ionic bondingTo define what is ionic bonding -Electrostatic attractions of opposite ions -Transfer of electron(s) -Non-directional force -Obey the rule of stability To draw electron diagramsTo draw electron diagrams To name and give chemical formula of the ionic compound ( both from mono or polyatomic ions)To name and give chemical formula of the ionic compound ( both from mono or polyatomic ions) To plan and describe experiments to realize what are electrolytes and non-electrolytes.To plan and describe experiments to realize what are electrolytes and non-electrolytes. To realize the nature of ions of an ionic compound.To realize the nature of ions of an ionic compound. To figure out the colour of an ionic compound in aqueous state.To figure out the colour of an ionic compound in aqueous state.

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32 Chemical bonding (attraction ) Ionic bonding Covalent bonding Forms between metals and nonmetals nonmetals and nonmetals Metallic bonding

33 Ionic bonding The reaction of sodium and chlorine. Sodium Chloride

34 Na          loses 1 e - + Na         unstable and reactive reactive sodium atom (Na) 2, 8, 1 Na ion + stablestable CATIONCATION

35 Cl gains 1 e - _  unstable and reactive reactive chlorine atom (Cl) 2, 8, 7 Cl ion - stablestable x x x x x x x x x x x x x xx xx Cl x x x x x x x x x x x x x xx xx ANIONANION

36 When a sodium atom and a chlorine atom react, the sodium atom loses one electron to the chlorine atom. As a result of this transfer of electron, two ions are formed. FORMATION OF IONIC BOND IONIC BONDING AND IONIC SUBSTANCES Sodium Chloride (Salt)

37 Na + Cl _ attracted by ionic bond Nature of ionic bond The attraction force is non-directional Cl _ In sodium chloride

38 Figure 8.15 Crystal of an ionic compound, sodium chloride.

39 Sodium chloride has a giant ionic structure. It consists of Na + and Cl – ions held together by ionic bonds.

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41 IONIC BOND is the strong non-directional electrostatic force of attraction between oppositely charged ions. An ionic bond is formed by the transfer of one or more electrons from one atom (or group of atoms) to another.

42 Monoatomic ion (consists of 1 atom only) Polyatomic ion (consists of 2 or more atoms ) Na + OH - K+K+ NO 3 - Ag + SO 4 2- Hg + I- Cl - Br -

43 1) All simple (single) metal ions are cations. 2a) All simple (single) non-metal ions are anions (except H + ). 2b) All polyatomic ions are anions (except NH 4 + ) 3)There is only one common polyatomic cation - NH )Polyatomic ions usually consist of non-metals only, but some consist of a metal and a non-metal. 5)When a metal forms only one cation, the ion has the same name as the metal. 6)Transition metals are rather unusual- the same metal can form more than one simple cation with different charges. To name each ion, a Roman numeral indicating the charge is written in brackets after the name of the metal.

44 7) Simple (single) anion names ending in –ide 8) Polyatomic anions containing oxygen ofter have names ending in –ate or –ite. The polyatomic anion with more oxygen is named as –ate, and that with less oxygen as –ite. 9)Ions with 4+ or 4- are uncommon. (unstable)

45 Questions Lead(II) dichromate Iron(III) oxide Potassium permanganate Zinc hydroxide KNO 3 CaCO 3 Ca(HCO 3 ) 2 Fe 2 (SO 4 ) 3

46 Objectives To define what is chemical bondingTo define what is chemical bonding To define what is ionic bondingTo define what is ionic bonding -Electrostatic attractions of opposite ions -Transfer of electron(s) -Non-directional force -Obey the rule of stability To draw electron diagramsTo draw electron diagrams To name and give chemical formula of the ionic compound ( both from mono or polyatomic ions)To name and give chemical formula of the ionic compound ( both from mono or polyatomic ions)

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