Ionic ,Covalent and Metallic Cambridge chemistry IGCSEc04.pptx

Ionic ,Covalent and Metallic Cambridge chemistry IGCSEc04.pptx

1. 1 IONIC, COVALENT AND METALLIC BONDING CHAPTER 4 The following content has not been through the Cambridge Assessment International Education endorsement process.

2. Think about the beautiful, colourful lights that are switched on at night. What are the gases that produce different coloured lights in decorative lighting called ‘neon lighting’? How many outer shell electrons are there in the outer shell of a neon atom? Noble gases do not readily react with othe r elements to form compounds. Why? Questions 2

3. 4.1 Ionic Bonding In this section, you will learn the following: Describe the formation of positive ions (cations) and negative ions (anions). State what an ionic bond is. Describe the formation of ionic bonds between elements from Group I and Group VII, including the use of dot-and-cross diagrams. Describe the formation of ionic bonds between ions of metallic and non-metallic elements, including the use of dot-and-cross diagrams. Describe the giant lattice structure of ionic compounds. Describe the properties of ionic compounds. Explain in terms of structure and bonding the properties of ionic compounds. 3

4. 4.1 Ionic Bonding Why are noble gases unreactive? Why do atoms of elements undergo reactions? How do atoms of elements undergo reactions? Outer shells of the noble gases They have fully filled outer shells, making their atoms stable. They undergo reactions to achieve the stable electronic configuration of a noble gas. They do so by gaining, losing or sharing electrons. 4

5. An atom becomes an ion when it gains or loses electrons . Metals form positively-charged ions called cations. Non-metals form negatively-charged ions called anions. How are ions formed? Gain of electron(s) + – Anion Cation Electrically Neutral Atom Loss of electron(s) 5

6. (to attain noble gas configuration) Positive ions or cations are formed when atoms lose electrons. Formation of positive ion Formation of a sodium ion (to attain noble gas configuration) Formation of a magnesium ion 6

7. Formation of negative ions Negative ions or anions are formed when atoms gain electrons. Formation of a chloride ion Formation of an oxide ion 7

8. Cations are usually ions of metals except (H+) and (NH 4 + ) Some metals can form more than one ion. For example, iron can form Fe 2+ and Fe 3+ ions. The charge on these ion is shown in the name of the compound formed. For example, iron(III) chloride contains the Fe 3+ ion. Common ions and their charges Names and formulae of some cations 8

9. Common ions and their charges (continued) Names and formulae of some anions 9

10. They consist of two or more atoms that are covalently bonded together. Ions with multiple atoms Ions with multiple atoms bonded together 10

11. An ionic bond is a strong electrostatic attraction between oppositely charged ions. Compounds that contain ionic bonds are called ionic compounds. For example, sodium reacts with chlorine to form an ionic compound called sodium chloride. The formation of an ionic bond is shown by a dot-and-cross diagram. In a dot-and-cross diagram, dots (●) represent the electrons in one atom; crosses (✕) represent the electrons of another atom. How are ionic compounds formed? Formation of an ionic bond in sodium chloride 11

12. How are ionic compounds formed? (continued) Dot-and-cross diagram for lithium fluoride Dot-and-cross diagram for potassium chloride Dot-and-cross diagram for sodium chloride 12

13. Formation of ionic bonds in magnesium chloride What happens when magnesium reacts with chlorine? 13

14. What happens when magnesium reacts with oxygen? The electronic configuration of magnesium atom is 2, 8, 2; oxygen atom is 2, 6. Therefore, magnesium atom loses two electrons while oxygen atom gains two electrons. Can you draw dot-and-cross diagrams showing the reaction between sodium and oxygen to form sodium oxide, Na 2 O? 14

15. are crystalline solids; have high melting and boiling points (they are not volatile ); have good electrical conductivity when molten or in aqueous solution, but not in solid state. Ionic compounds What are the physical properties of ionic compounds? 15

16. Ionic compounds form giant lattice structures. In the lattice structure of sodium chloride, each Na + ion is surrounded by six C l – ions; each C l – ion is surrounded by six Na + ions; the overall ratio of Na + to C l – is 1 : 1. Hence, NaC l is the formula unit of sodium chloride. The formula of sodium chloride is NaC l . Ions held in regular pattern by ionic bond s . Strong electrostatic attraction between oppositely charged ions Relating the physical properties of ionic compounds to their structure and bonding Giant lattice structure The giant lattice structure of sodium chloride can be represented by either of the diagrams above. 16

17. Ions are free to move . High melting and boiling points In an ionic compound: The electrostatic attractions between the oppositely charged ions are strong; A large amount of heat is needed to overcome these strong attractive force; As a result, ionic compounds have high melting and boiling points. Good electrical conductivity when molten or in aqueous solution, but not in solid state Ions are not free to move . The ions are free to move when an ionic compound is dissolved in water. 17

18. 4.2 Covalent Bonding and Simple Molecules In this section, you will learn the following: State what a covalent bond is. Describe the formation of covalent bonding in simple molecules (e.g. H 2 , C l 2 , H 2 O, CH 4 , NH 3 and HC l ). Use dot-and-cross diagrams to show the electronic configurations in these and similar molecules. Describe the formation of covalent bonds in simple molecules (e.g. CH 3 OH, C 2 H 4 , O 2 , CO 2 and N 2 ). Use dot and cross diagrams to show the electronic configurations in these and similar molecules. Describe the properties of simple molecular compounds. Explain in terms of structure and bonding the properties of simple molecular compounds. 18

19. 4.2 Covalent Bonding and Simple Molecules How are covalent compounds formed? A covalent bond is formed when a pair of electrons is shared between two atoms leading to noble gas electronic configurations. Examples of d ifferent covalent bonds formed When atoms combine by sharing electrons, molecules are formed. Covalent bonds can be formed between atoms of the same element; atoms of different elements. 19

20. Molecules of elements Formation of a covalent bond in a hydrogen molecule  20

21. Single covalent bond The bond formed between two atoms by sharing one pair of electrons. Different ways of representing a hydrogen and a chlorine molecule 21

22. Double covalent bond The bond formed between two atoms by sharing two pairs of electrons . Formation of covalent bonds in an oxygen molecule Different ways of representing an oxygen molecule 22

23. Triple covalent bond The bond formed between two atoms by sharing three pairs of electrons . Formation of covalent bonds in a nitrogen molecule Different ways of representing a nitrogen molecule 23

24. S tr u c tu r al formula M odel M olecular formula Formation of covalent bonds in a water molecule Molecules of compounds When atoms of different elements are joined together by covalent bonding, a covalent compound or simple molecular compound is formed. Different ways of representing a water molecule 24

25. Molecules of compounds (continued) Formation of covalent bonds in a methane molecule  Different ways of representing methane, ammonia, and hydrogen chloride molecules 25

26. Molecules of compounds Different ways of representing methanol , carbon dioxide and ethene molecule s Formation of covalent bonds in a carbon dioxide molecule 26

27. 27 What are the physical properties of covalent compounds? The examples learnt so far are known as simple molecules . They have simple molecular structures . Simple molecules: have low melting and boiling points (they have a high volatility);  and are poor electrical conductors. 

28. 4.3 Giant Covalent Structures In this section, you will learn the following: Describe the giant covalent structures of graphite and diamond. Relate the structures and bonding of graphite and diamond to their uses. Describe the giant covalent structure of silicon(IV) oxide. Describe the similarities in properties between diamond and silicon(IV) oxide . 28

29. 4.3 Giant Covalent Structures A giant covalent structure is a three-dimensional regular arrangement of atoms or molecules joined by strong covalent bonds. Examples Diamond Graphite Silicon(IV) oxide Allotropes of carbon Allotropes are different structural forms of the same element that have the same physical state. 29 Allotropes of carbon

30. What are the physical properties of giant covalent substances? High melting and boiling points A giant covalent structure consists of a large number of atoms that are held together by strong covalent bonds. A large amount of energy is required to break these bonds, in order to melt or boil the substance. In giant covalent substances (except graphite), all the outer electrons of the atoms are used to form covalent bonds. Thus, there are no delocalised electrons that move through the structure to conduct electricity. Do not conduct electricity (except graphite) 30

31. 31 Diamond Structure of diamond

32. Graphite Structure of graphite 32

33. 33 Uses of graphite Uses of diamond

34. Silicon(IV) oxide Structure of Silicon(IV) oxide 34

35. In this section, you will learn the following: Describe metallic bonding. Explain in terms of structure and bonding the properties of metals. 4.4 Metallic Bonding 35

36. 4.4 Metallic Bonding Metal lattice structure What is a metallic bond? A metallic bond is the electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons. In the metal lattice , M etal atoms lose their outer electrons and become positively-charged ions. The outer electrons no longer belong to any metal atom and are said to be delocalised. The outer electrons move freely between the metal ions like a cloud of negative charge. Hence, the metal lattice structure is described as a lattice of positive ions surrounded by a ‘sea' of delocalised electrons. Metal lattice structure 36

37. What are the physical properties of metals? Delocalised electrons conduct electricity Good electrical conductivity 37

38. What are the physical properties of metals? Before a force is applied, the metal atoms form an orderly and rigid arrangement. When a force is applied to a metal, the layers of metal atoms can slide over each other through the ‘sea’ of delocalised electrons Malleable and ductile 38

39. What have you learnt? ? ? ? 39

40. What have you learnt? 40

41. Acknowledgements