Ionic Compounds. Chapter 5.6

Transcription

1 Ionic Compounds Chapter 5.6

2 Ionic Compounds Ionic compounds are made up by the chemical combination of metallic and non-metallic elements.

3 Ionic Compounds Ionic compounds are made up by the chemical combination of metallic and non-metallic elements. Most rocks, minerals and gemstones are ionic compounds.

4 Ionic Compounds Ceramics, bricks and kitchen crockery are made from clays which contain ionic compounds.

5 Ionic Compounds While most of the previously mentioned are made up of mixtures of different ionic compounds table salt is a pure ionic compound made up of sodium chloride (NaCl)

6 UNDERSTANDING CHEMICAL REACTIONS Ionic Bonding LecturePLUS Timberlake 6

7 Chemical Bonds Attraction between two or more atoms Interaction between valence electrons Ionic bonds Covalent bonds LecturePLUS Timberlake 7

8 Valence Electrons review review Electrons in the highest (outer) electron level Have most contact with other atoms Known as valence electrons Outer shells of noble gases contain 8 valence electrons (except He = 2) Example: Ne 2, 8 Ar 2, 8, 8 LecturePLUS Timberlake 8

9 How exactly are the particles arranged? review Bohr Model of the atom: Reviewers think this could lead to misconceptions! The 3 rd ring can hold up to 8 e - The 4 th ring and any after can hold up to 32 e - All of the protons and the neutrons The 1 st ring can hold up to 2 e - The 2 nd ring can hold up to 8 e - LecturePLUS Timberlake 9

10 Electron Dot Structures review Symbols of atoms with dots to represent the valence-shell electrons 1A 2A 3A 4A 5A 6A 7A 8A LecturePLUS Timberlake 10

11 Learning Check A. X would be the electron dot formula for 1) Na 2) K 3) Al B. X would be the electron dot formula 1) B 2) N 3) P LecturePLUS Timberlake 11

12 Solution A. X would be the electron dot formula for 1) Na 2) K B. X would be the electron dot formula 2) N 3) P LecturePLUS Timberlake 12

13 Octet Rule An octet in the outer shell makes atoms stable Electrons are lost, gained or shared to form an octet Unpaired valence electrons strongly influence bonding LecturePLUS Timberlake 13

14 Electron Dot Structures review Symbols of atoms with dots to represent the valence-shell electrons 1A 2A 3A 4A 5A 6A 7A 8A H He: Li Be B C N O : F :Ne : Na Mg Al Si P S :Cl :Ar : LecturePLUS Timberlake 14

15 IONS review An ion is an atom that has gained or lost electrons meaning it is negatively or positively charged. Atoms do this to get a full outer (valence) electron shell and so becomes more stable. The atom will get a full outer shell the simplest way it can, e.g. for 12 Mg: - Electron arrangement of 2, 8, 2 - it will LOSE 2 electrons (become 2, 8) - Now it has 10 electrons, but still has 12 protons. It has a 2+ charge. The ion is called Mg 2+. Superscript is used for ion charges LecturePLUS Timberlake 15

16 Ions review When atoms lose or gain electrons, they become ions. Cations are positive and are formed by elements on the left side of the periodic chart. Anions are negative and are formed by elements on the right side of the periodic chart. LecturePLUS Timberlake 16

17 The ionic bonding model Chemists believe that when metallic and non-metallic atoms react to form ionic compounds the following steps occur: 1. Metal atoms lose electrons to non-metallic atoms and become positively charged metal ions. 2. Non-metal atoms gain electrons from the metal atoms and so become negatively charged nonmetal ions.

18 The ionic bonding model Chemists believe that when metallic and non-metallic atoms react to form ionic compounds the following steps occur: 3. Large numbers of positive and negative ions formed in this way then combine to form a three-dimensional lattice.

19 The ionic bonding model Chemists believe that when metallic and non-metallic atoms react to form ionic compounds the following steps occur: 4. The three dimensional lattice is held together strongly by electrostatic forces of attraction between positive and negative ions. This electrostatic force is called ionic bonding.

20 Ionic bonding Whenever a non-metal reacts with a metal to form a new compound, ionic bonding is responsible. Compounds made from ionic bonds form GIANT STRUCTURES (not molecules) LecturePLUS Timberlake 20

21 Ionic compounds form from the inside out as solid crystals. Ionic compounds are like a solid stack of bricks. A salt shaker contains thousands of small pieces of NaCl. (c) McGraw Hill Ryerson 2007 See pages

22 Example: sodium chloride Na + Cl 2,8,1 2,8,7 LecturePLUS Timberlake 22

23 Electron Transfer Diagrams When sodium and chloride react together sodium loses an electron and chlorine gains an electron.

24 Sodium Chloride What is happening: Chlorine molecules splitting into separate chlorine atoms Electrons being transferred from sodium atoms to chlorine atoms positively charged sodium and negatively charged chlorine ions are being formed. Sodium and chloride ions combining to form a three dimensional lattice.

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26 Notes: When a non-metal atom gains one or more electrons, the name of the negative ion ends in ide. When a metal atom loses one or more electrons the name of the positive ion is the same as the metal and is always named first. For example: sodium chloride

27 Magnesium Oxide What are the electron configurations for Magnesium and Oxygen? How many electrons does magnesium need to lose to get a full outer shell? How many electrons does oxygen need to gain to get a full outer shell? Draw an electron transfer diagram. What is the electrovalency of a magnesium ion and an oxide ion?

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29 Another example of ionic bonding Magnesium and chlorine What are the electron configurations for Mg and Cl? how can this work? LecturePLUS Timberlake 29

30 To obtain full outer shells: Mg atom must lose 2 electrons Cl atom must gain 1 electron. So when Mg reacts with Cl, each Mg atom reacts with two chlorine atoms, to form magnesium chloride. LecturePLUS Timberlake 30

31 MgCl2

32 The ions form a giant ionic structure. There are two chloride ions for each magnesium ion. The formula for magnesium chloride is MgCl 2 LecturePLUS Timberlake 32

33 The compound has no overall charge. LecturePLUS Timberlake 33

34 Properties of Ionic Compounds Think of the properties of rocks, bricks, crockery and table salt. What properties do they share? Have high melting and boiling temperatures. Are hard but brittle They also: Do NOT conduct electricity in the solid state They will only conduct electricity if they are melted or dissolved in water

35 Structure of ionic compounds The physical properties of ionic compounds are very different from metals. The structure of ionic compounds must therefore be very different from those present in metals. What do we already know about ionic compounds.

36 What do the properties tell us?

37 Structure From the properties we can conclude: The forces between the particles are strong. There are no free-moving electrons present, unlike in metals. There are charged particles present, but in solid state they are not free to move. When an ionic compound melts, however, the particles are free to move and the compound will conduct electricity.

38 Names and Formulas

39 Text book practice P 191#1-7 P 195 # 1-8 FROG Book P 187# 1-10 P189 #1-4 LecturePLUS Timberlake 39

40 Using the ionic bonding model to explain the properties of sodium chloride

41 High Melting Temperature Ever noticed that when you eat fish and chips the food may be hot but the salt does not melt. This is because to melt and ionic solid energy must be provided to allow the ions to break free and move. NaCl has a high melting temp, this indicates a large amount of energy is needed to reduce the electrostatic attraction between the oppositely charged ions and allow them to move freely.

42 Hardness and Brittleness Unlike metals ionic compounds are not malleable. They break when beaten. A force can disrupt the strong electrostatic forces holding the lattice in place. A sodium chloride crystal cannot be scratched easily but if a strong force (a hammer blow) is applied it will shatter. This is because the layers of ions will move relative to each other due to the force. During this movement, ions of like charge will become adjacent to each other. Resulting in repulsion

43 Hardness and Brittleness Figure 6.4 The repulsion between like charges causes this sodium chloride crystal to shatter when it is hit sharply.

44 Electrical Conductivity In the solid form, ions in sodium chloride are held in the crystal lattice and are not free to move so cannot conduct electricity. When the solid melts the ions are free to move. The movement of these charged particles to an electrode completes an electrical circuit. In a similar way, when sodium chloride dissolves in water, the ions separate and are free to move towards the opposite charge.

45 Conducting Electricity

46 Reactions of metals with non-metals Metallic atoms have low ionisation energies and low electronegativities. Non-metallic atoms have high ionisation energies and low electronegativities. In other words metallic atoms lose electrons easily and non-metallic atoms gain electrons easily.

47 Ionic Compounds So the metal atoms lose an electron to the non-metal atoms. In doing so, both atoms will often achieve the electronic configuration of the nearest noblest gas, which is particularly stable.

48 Your Turn Page 195 Questions 10 to 13

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