Bonding Series 3 Ionic Bonding 1 Introduction This is the final booklet in the Bonding Series. A lot of the material here was studied in Year 11. There is lots of practise material here. Most marks for ionic bonding should never be lost in an exam. The past paper questions with commentary and answers are found at the rear of the booklet. Pay attention to the comments about the tougher questions Enjoy! S de Naipir 2 Describing ionic bonding with dot and cross diagrams There are three parts to describing ionic bonding with dot and cross. Part 1: Draw the atoms showing the outer electrons and draw a curved arrow to show the electrons moving from the metal atom to the non-metal atom. Here we are using a group 1 metal atom, lithium and group 7 atoms. Notice only the outer electrons are drawn. Call this stage Before. 3 Practising Before stage with lithium atoms and halogen atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. Potassium atoms are on the left and halogen atoms are on the right. LiF LiCl LiBr 4 LiI Practising Before stage with sodium atoms and halogen atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. Potassium atoms are on the left and halogen atoms are on the right. NaF NaCl 5 NaBr NaI 6 Practising Before stage with potassium atoms and halogen atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. Potassium atoms are on the left and halogen atoms are on the right. KF KCl KBr 7 KI Part 2: The After stage. The dot and cross diagrams for the ions formed after electron donation LiF LiCl 8 LiBr LiI 9 Practising Part 2: The After stage. Draw the dot and cross diagrams for the ions formed in the following ionic compounds: LiF LiCl LiBr 10 LiI Part 3: The final statement The electrostatic forces of attraction between the cations and anions are the ionic bond. Write out the final statement 5 times 11 Putting all steps together: The model answer The electrostatic forces of attraction between the cations and anions is the ionic bond. 12 Group 2 and Halogens Group 2 metal atoms have 2 electrons in their outer shells Group 7 Halogens have 7 electrons in their outer shells. Group 2 metal atoms donate 2 electrons to non-metal atoms, but halogens atom can only accept 1 electron. Therefore, 2 halogen atoms are needed to accept the donated electrons. Here are the before bonding and after diagrams showing an Mg atom donating its two electrons to 2 F atoms to form an Mg2+ ion and 2 F- ions. Before After The electrostatic forces of attraction between the cations and anions is the ionic bond. 13 Practising Before stage with Mg atoms and 2 halogen atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. MgF2 MgCl2 14 MgBr2 MgI2 15 Practising Before stage with Ca atoms and 2 halogen atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. CaF2 CaCl2 16 CaBr2 CaI2 17 Practising Part 2: The After stage. Draw the dot and cross diagrams for the ions formed in the following ionic compounds: MgF2 MgCl2 MgBr2 18 MgI2 CaF2 CaCl2 19 CaBr2 CaI2 20 Part 3: The final statement The electrostatic forces of attraction between the cations and anions are the ionic bond. Write out the final statement 5 times 21 Practising the full model exam answer. (All 3 stages) Describe, using dot and cross diagrams, the ionic bonding of the following ionic compounds MgF2 MgCl2 22 MgBr2 MgI2 23 CaF2 CaCl2 24 CaBr2 CaI2 25 Group 2 and Group 6 Group 2 metal atoms have 2 electrons in their outer shells Group 6 non-metal atoms have 6 electrons in their outer shells. Group 2 metal atoms donate 2 electrons to group 6 non-metal atoms, Here are the before bonding and after diagrams showing an Mg atom donating its two electrons to 1 O atom to form an Mg2+ ion and an O2- ions. Before After The electrostatic forces of attraction between the cations and anions are the ionic bond. 26 Practising Before stage with Mg atoms and Group 7 atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. MgO MgS 27 MgSe Practising Before stage with Ca atoms and Group 6 atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. CaO 28 CaS CaSe 29 Practising Part 2: The After stage. Draw the dot and cross diagrams for the ions formed in the following ionic compounds: MgO MgS MgSe 30 CaO CaS CaSe 31 Part 3: The final statement The electrostatic forces of attraction between the cations and anions are the ionic bond. Write out the final statement 5 times 32 Practising the full model exam answer. (All 3 stages) Describe, using dot and cross diagrams, the ionic bonding of the following ionic compounds MgO MgS 33 MgSe CaO 34 CaS CaSe 35 Group 1 and Group 6 Group 1 metal atoms have 1electron in their outer shells Group 6 non-metal atoms have 6 electrons in their outer shells. 2 Group 1 metal atoms each donate 1 electron to group 6 non-metal atoms, Here are the before bonding and after diagrams showing 2 Na atoms donating electrons to 1 O atom to form 2 Na+ ions and 1 O2- ion. Before After The electrostatic forces of attraction between the cations and anions are the ionic bond. 36 Practising Before stage with Li atoms and Group 6 atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. Li2O Li2S 37 Li2Se Practising Before stage with sodium atoms and Group 6 atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. Na2O 38 Na2S Na2Se 39 Practising Before stage with Potassium atoms and Group 6 atoms. Add the outer electrons to both atoms in each example and then draw the arrow to show electron movement. K2O K2S 40 K2Se Practising Part 2: The After stage. Draw the dot and cross diagrams for the ions formed in the following ionic compounds: Li2O Li2S 41 Li2Se Na2O Na2S 42 Na2Se K2O K2S 43 K2Se Na2Se 44 Part 3: The final statement The electrostatic forces of attraction between the cations and anions are the ionic bond. Write out the final statement 5 times 45 Practising the full model exam answer. (All 3 stages) Describe, using dot and cross diagrams, the ionic bonding of the following ionic compounds Li2O Li2S 46 Li2Se Na2O 47 Na2S Na2Se 48 K2O K2S 49 K2Se 50 Ionic structures You must know the following two ionic structures: NaCl A giant 3D ionic lattice • • Each Na+ ion is surrounded by 6 Cl-ions Each Cl- ion is surrounded by 6 Na+ ions Therefore, the crystal co-ordination number in NaCl is 6:6 51 Cesium Chloride Giant 3D Ionic Lattice • • Each Cs+ ion is surrounded by 8 Cl-ions Each Cl- ion is surrounded by 8 Cs+ ions Make sure you label the ions. The red ions are Cl- ions. The green ion is Cs+ Therefore, the crystal co-ordination number in CsCl is 8:8 52 Properties of Ionic Solid Structures Properties Reason for properties Molten or dissolved salts have free ions to carry the charge. Molten or dissolved salts conduct electricity Solid ionic compounds don’t have free ions or electrons to carry the charge Solid Ionic compounds Salts are hard because of tight packing lattices, say, the positive and negative ions are strongly attached among themselves. Brittle (break easily) If pressure is applied to an ionic solid, ions of similar charges may be forced to closer together. The electrostatic repulsion can be enough to split the ionic lattice. Melting point is high, because lots of energy is needed to overcome the strong electrostatic forces of attraction between the cations and ions. Melting Point 53 Explain why are ionic structures are hard, brittle and have high melting points? Explain why ionic solids don’t conduct electricity? Explain when ionic compounds conduct electricity and why? 54 Solubility of ionic solids Some salts dissolve in water. Here’s what happens to the ions when they are added to water The δ- of water orient themselves around cations ( + ions). The δ- of water orient themselves around anion (- ions). Salts dissolves when the attraction between the polar water molecules and the ions is greater than the energy of salt’s lattice energy. 55 Note: You can be asked to draw these diagrams for any salt that dissolves in water. You have practice this on following pages: Show how, and explain why, the following salts dissolve in water LiF KBr 56 NaI NaCl 57 Past paper Questions with Commentary Comment This question appeared on the mock exam and was poorly answered. Many students drew covalent dot and cross diagrams. It appears that many thought that dot and cross diagrams are only for covalent compounds. The key information is magnesium fluoride. This contains a metal and a non-metal. Therefore, it is a salt (ionic compound). Comment This is a simple recall question. You either remember it or you don’t. CsCl has a coordination number 8:8 Beware that the examiner could use CsF, CsBr, CsI in this type of question. Answer 8 58 Comment This is a tough question on structures. You must understand and know the melting point and electrical conductivity of metals, ionic, giant covalent, and simple covalent structures. Answer: A is simple molecular Why? Low melting point and does not conduct electricity. D is ionic Why? High melting point and does not conduct electricity when solid, but does when dissolved 59 B probably giant covalent, but could be ionic Why? Probably giant covalent due to high melting point and does not conduct electricity. Could be ionic because not all ionic solids (salts) are soluble. The Bunsen couldn’t melt the salt to allow electrical conductivity to be tested when molten. C is probably metallic, but could be giant covalent as graphite conducts electricity Why? Both metals and graphite have high melting points and conduct electricity Comment On the mark scheme the words probably and could be are in bold. If you leave these words out, you will not get the marks. Unfair? I think so. Comment A straight-forward question. Remember no covalent diagrams. 60 Comment This is a tough question. Answer Sodium and Oxygen because they have the largest difference in electronegativities. Comment This is a simple question. 61 Comment This question is a tough. You have to how NaCl is structured within this cube, so we we look at that here: The grey lines are guiding lines. Notice how the cations and anions alternate on different lines. Here the diagram without the guiding lines: 62 Answer To answer the question, complete the diagram using Mg2+ and S2-instead of Na+ and Cl- I have included a practise sheet for you to use when practising this type of question. 63 Practise Sheet 64 Comment A recall question. You either remember it or you don’t Answer 8 Comment An easy question 65 Comment This is an easy question. You simply look for compounds made of metal and non-metals ions. You must know your ions. Answer MgO and Al2O3 66 Comment A straight-forward question Answer Co-ordinaton number of NaCl is 6:6 67 Comment This is a straight-forward question. I would recommend you draw the diagram. See page 55. Just replace the cations and anion for the ions in this question. Comment An easy question 68 Comment A tough question. Ionic bonds get some covalent character when the positive ion is small with a high positive charge and the negative ion is large. The highly charged + ion will pull the large – ion’s electron cloud towards itself. This is like a covalent bond. Answer Positive ions must increase charge and decrease size (in order to pull the negative ion’s electron cloud) Negative ions must increase charge and increase size (in order to have its negative electron cloud pulled by the positive ion) 69 Comment An easy question Comment An easy question Comment An easy question. You must know your ions to work out the formula of lithium hydride, LiH See page 67 to help you answer this question. Just replace Na+ and Cl- with Li+ and H- 70 Comment An easy question Comment An interesting question. The smaller black ion is Li- and the larger white ion is Br – How would you work that out? Li is smaller than Br. Answer The smaller black ion is Li- and the larger white ion is Br – Crystal co-ordination number of LiBr is 6:6 71 Comment An easy question Comment A NaCl is ionic and soluble. Be careful you read part (b) correctly. Answer (a) Sodium chloride (b) Iodine 72 Comment A good comparison question. I have added blank cubes to allow you to practise drawing this shape Answer The small white ions are Cl- and large black ion is Cs+ Crystal co-ordination number of CsCl is 8:8 Cs+ is larger than Na+ so more Cl- ions can fit around it. 73 Draw CsCl. State its crystal co-ordination number and explain it differs from NaCl’s 74 Comment An easy question. The small white ions are Na+ and large white ions are Cl- Comment Most of this question is easy. It is important to include a labelled diagram as part of your answer. The last bullet point is difficult. 75 Answer You should be able to answer the first two bullet points. The answer to the third bullet point is given below: In the electrostatic forces of attraction between the ions, like same charge ions repel and differently charged ions attract. Comment The water molecules mentioned in (a) are not the water molecules in the formula of the compound. Ignore the water molecules in the formula. You must know your ions. The ions made with Ba(OH)2 dissolves in water are Ba2+ and OH- Answer See page 55 to help you answer this question just replace Na+ with Ba2+ and Cl- with OH- 76
