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1 CHAPTER 6 Ionic Bonding © 2013 Marshall Cavendish International (Singapore) Private Limited.

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1 1 CHAPTER 6 Ionic Bonding © 2013 Marshall Cavendish International (Singapore) Private Limited

2 6.1The Stable Electronic Configuration of a Noble Gas 6.2Forming Ions 6.3Ionic Bond: Transferring Electrons 6.4Chemical Formulae of Ionic Compounds 6.5Structure and Physical Properties of Ionic Compounds Chapter 6 Ionic Bonding 2

3 Learning Outcome 6.1The Stable Electronic Configuration of a Noble Gas describe the stable electronic configuration of a noble gas. At the end of this section, you should be able to: 3

4 What are Noble Gases? Elements that belong to Group 0 of the Periodic Table Examples: He, Ne, Ar, Kr and Rn Atoms of noble gases are stable and unreactive. They exist in nature as single atoms The Stable Electronic Configuration of a Noble Gas

5 What is the Noble Gas Structure? Noble gases have full or complete outer shells. Helium has a duplet configuration All other noble gases have an octet configuration (2 outer electrons). (8 outer electrons) The Stable Electronic Configuration of a Noble Gas

6 Why Do Atoms React? Atoms of most other elements are reactive because they do not have the noble gas structure (i.e. their outer shells are not fully-filled). Atoms of these elements lose, gain or share outer electrons to attain the noble gas configuration and form compounds The Stable Electronic Configuration of a Noble Gas

7 Chemical Bonding Ionic bonding Covalent bonding Atoms share electrons to attain noble gas configuration Atoms gain or lose electrons to attain noble gas configuration 7 6.1The Stable Electronic Configuration of a Noble Gas

8 Chapter 6 Ionic Bonding 8 6.1The Stable Electronic Configuration of a Noble Gas 6.2Forming Ions 6.3Ionic Bond: Transferring Electrons 6.4Chemical Formulae of Ionic Compounds 6.5Structure and Physical Properties of Ionic Compounds

9 describe the formation of positive ions (cations) and negative ions (anions) to achieve the noble gas configuration. 9 Learning Outcome At the end of this section, you should be able to: 6.2 Forming Ions

10 What is an Ion? Recall: Atoms have an equal number of protons and electrons. They are electrically neutral. An atom loses or gains electrons to form ions. Ions are charged particles. No. of electrons ≠ No. of protons Forming Ions

11 Ions can be positively- or negatively-charged. Positively-charged ions are called cations. Negatively-charged ions are called anions. URL Forming Ions What is an Ion?

12 Formation of Cations Atoms of metals lose electrons to form positively-charged ions called cations. In this way, they achieve the noble gas configuration Forming Ions

13 The Na atom loses one outer electron to form the Na + ion. Why? To achieve stable octet (noble gas) configuration. Example 1: Formation of sodium (Na + ) ion Na atom Electronic configuration: 2, 8, 1 Number of protons = 11 Number of electrons = 11 Neon (2, 8) Forming Ions

14 Na atom: 11p, 12n, 11e 2, 8, 1 2, 8 sodium atom loses one outer electron + Neutral Na atom Positively-charged Na + ion Charge = 11p + 11e = (+11) + (–11) = 0 Na + ion: 11p, 12n, 10e Charge = 11p + 10e = (+11) + (–10) = Forming Ions Example 1: Formation of sodium (Na + ) ion

15 Charge = 20p + 20e Ca 2+ ion: 20p, 20n, 18e 2, 8, 8, 2 2, 8, 8 Ca atom: 20p, 20n, 20e 2+ calcium atom loses two outer electrons Neutral Ca atom Positively-charged Ca 2+ ion = 20(+1) + 20(–1) = (+20) + (–20) = 0 Charge = 20p + 18e = 20(+1) + 18(–1) = (+20) + (–18) = Forming Ions Example 2: Formation of calcium (Ca 2+ ) ion

16 MetalIonFormula of ion sodiumsodium ionNa + potassiumpotassium ionK+K+ calciumcalcium ionCa 2+ magnesiummagnesium ionMg 2+ aluminiumaluminium ionA l 3+ Common Cations and Their Charges Forming Ions

17 Formation of Anions Atoms of non-metals gain electrons to form negatively-charged ions called anions. In this way, they achieve the noble gas configuration Forming Ions

18 C l atom Electronic configuration: 2, 8, 7 Number of protons = 17 Number of electrons = 17 What happens in the formation of a chloride ion? The chlorine atom gains one electron in its outer shell to achieve a stable octet (noble gas) configuration. Argon (2, 8, 8) Forming Ions Example 1: Formation of chloride (C l – ) ion

19 chlorine atom gains one electron 2, 8, 7 C l atom: 17p, 18n, 17e C l – ion: 17p, 18n, 18e Neutral C l atom Negatively charged C l – ion Charge = 17p + 17e = (+17) + (–17) = 0 Charge = 17p + 18e = (+17) + (–18) = –1 2, 8, Forming Ions Example 1: Formation of chloride (C l – ) ion

20 oxygen atom gains two electrons O atom: 8p, 8n, 8e O 2– ion: 8p, 8n, 10e Neutral O atom Negatively charged O 2– ion Charge = 8p + 8e = (+8) + (–8) = 0 Charge = 8p + 10e = (+8) + (–10) = –2 2, 8 2– 20 2, Forming Ions Example 2: Formation of oxide (O 2– ) ion

21 Non-metalIonFormula of ion chlorinechloride ionCl–Cl– brominebromide ionBr – oxygenoxide ionO 2– sulfursulfide ionS 2– Common Anions and Their Charges Forming Ions

22 Why do metals lose electrons to form positive ions (cations) but non-metals gain electrons to form negative ions (anions)? 22

23 Chapter 6 Ionic Bonding The Stable Electronic Configuration of a Noble Gas 6.2Forming Ions 6.3Ionic Bond: Transferring Electrons 6.4Chemical Formulae of Ionic Compounds 6.5Structure and Physical Properties of Ionic Compounds

24 Learning Outcome describe how an ionic bonds are formed between metals and non-metals. At the end of this section, you should be able to: Ionic Bond: Transferring Electrons

25 Examples: Group VII: Fluorine, chlorine Group VI: Oxygen, sulfur Examples: Group I: Sodium, potassium Group II: Magnesium, calcium Ionic Bonding Ionic bonds are formed between metals and non-metals. This is done through the transfer of electron(s) from metals to non-metals Ionic Bond: Transferring Electrons

26 Metallic atom Non-metallic atom loses electron(s) gains electron(s) Positive ion (cation) Negative ion (anion) electrostatic forces of attraction Ionic Bonding (hold oppositely charged ions together) Ionic Bond: Transferring Electrons

27 Step 1: Formation of Positive Ions Each sodium atom (Na) loses its single outer electron to form a positively-charged sodium ion (Na + ). Na Na + + e − 2, 8, 1 2, 8 Formation of Ionic Compound Example 1: Sodium chloride Ionic Bond: Transferring Electrons

28 Step 2: Formation of Negative Ions Each chlorine atom gains an electron from a sodium atom to form a negatively-charged chloride ion (Cl − ). Cl –Cl – ClCl 2, 8, 72, 8, 8 + e − Ionic Bond: Transferring Electrons

29 Sodium and chlorine react in the ratio of 1 : 1 to form sodium chloride (NaC l ). Sodium atom 2, 8, 1 Chlorine atom 2, 8, 7 Sodium ion 2, 8 Chloride ion 2, 8, 8 Electrostatic forces of attraction Step 3: Formation of Ionic Bonds Gains one electron Loses one electron URL Ionic Bond: Transferring Electrons

30 Chlorine atoms gain one electron each. Chloride ion 2, 8, 8 Chloride ion 2, 8, 8 Magnesium ion 2, 8 Magnesium atom loses two electrons. Magnesium reacts with chlorine in the ratio of 1 : 2 to form magnesium chloride (MgC l 2 ). Example 2: Magnesium chloride Ionic Bond: Transferring Electrons

31 Chapter 6 Ionic Bonding The Stable Electronic Configuration of a Noble Gas 6.2Forming Ions 6.3Ionic Bond: Transferring Electrons 6.4Chemical Formulae of Ionic Compounds 6.5Structure and Physical Properties of Ionic Compounds

32 Learning Outcome deduce the chemical formula of an ionic compound from the charges on the ions and vice versa. At the end of this section, you should be able to: Chemical Formulae of Ionic Compounds

33 Chemical Formulae of Ionic Compounds The formula of an ionic compound is constructed by balancing the charges on the positive and negative ions. All the positive charges must equal all the negative charges in an ionic compound Chemical Formulae of Ionic Compounds

34 Since 1 × (+2 charge) balances out 1 × (−2 charge), Example: Magnesium oxide Magnesium forms Mg 2+ ions. Oxygen forms O 2− ions. Mg 2+ O 2− The formula is MgO. Charge: +2 Charge: − Chemical Formulae of Ionic Compounds

35 Since 1 × (+2 charge) balances out 2 × (−1 charge), Copper ionHydroxide ion Cu 2+ OH − The formula is Cu(OH) 2. Charge: +2 Charge: −1 To balance the charges, multiply the smaller charge (−1) by 2 to make it equal to +2. Example: Copper(II) hydroxide Chemical Formulae of Ionic Compounds

36 Example 1 Write the chemical formula of aluminium oxide. aluminium ion oxide ion A l 3 + O 2 − Al2O3Al2O3 Charge: +3 Charge: −2 36 Therefore, the formula is A l 2 O Chemical Formulae of Ionic Compounds

37 Since ‘2’ is a common factor, it can be removed. Therefore, the formula is CaCO 3. CaCO 3 URL Example 2 Write the chemical formula of calcium carbonate. calcium ion carbonate ion Ca 2 + CO 3 2 − Ca 2 (CO 3 ) 2 Charge: +3 Charge: − Chemical Formulae of Ionic Compounds

38 Chapter 6 Ionic Bonding The Stable Electronic Configuration of a Noble Gas 6.2Forming Ions 6.3Ionic Bond: Transferring Electrons 6.4Chemical Formulae of Ionic Compounds 6.5Structure and Physical Properties of Ionic Compounds

39 Learning Outcomes state that ionic compounds form giant lattice structures; At the end of this section, you should be able to: deduce the formulae of ionic compounds from their lattice structures; 39 relate the physical properties of ionic compounds to their lattice structures. 6.5Structure and Physical Properties of Ionic Compounds

40 Ionic compounds form giant ionic structures. Structure of Ionic Compounds Also known as giant lattice structures or crystal lattices Consist of an endlessly repeating three-dimensional lattice of positive and negative ions Ions are closely packed, arranged in an orderly manner and held in place by ionic bonds Structure and Physical Properties of Ionic Compounds

41 Sodium ions and chloride ions alternate with each other. Structure of NaC l Three-dimensional arrangement of sodium ions and chloride ions 41 Sodium chloride crystal 6.5Structure and Physical Properties of Ionic Compounds

42 Strong forces of attraction between ions in crystal lattice A large amount of energy is required to overcome these forces of attraction between ions. Structure of NaC l Na + Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Structure and Physical Properties of Ionic Compounds

43 43 Each sodium ion is surrounded by six chloride ions. Each chloride ion is surrounded by six sodium ions. Cl − ion Na + ion The ratio of sodium ions to chloride ions is 1 : 1. Hence, the formula unit of sodium chloride is NaCl. Structure of NaC l 6.5Structure and Physical Properties of Ionic Compounds

44 High melting and boiling points Non-volatile Exist as solids at room temperature Melting and Boiling Points of Ionic Compounds Na + Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Structure and Physical Properties of Ionic Compounds

45 Usually soluble in water Solubility of Ionic Compounds Usually insoluble in organic solvents E.g. ethanol, turpentine, petrol Water molecules dissolve in water URL Cl–Cl– Na + Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Cl–Cl– Structure and Physical Properties of Ionic Compounds

46 aqueous NaC l solid NaC l molten NaC l Electrical Conductivity of Ionic Compounds Structure and Physical Properties of Ionic Compounds

47 Electrical Conductivity of Ionic Compounds Ionic compounds conduct electricity in the molten and aqueous states. They do not conduct electricity in the solid state. In the molten and aqueous states, mobile ions are present. Mobile ions conduct electricity Structure and Physical Properties of Ionic Compounds

48 Concept Map 48 Chapter 6 Ionic Bonding


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