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

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

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

4. 6.1 The Stable Electronic Configuration of a Noble Gas
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.
Provide a brief introduction to the idea of noble gases.
Have students recall from Chapter 4 that neon, which is a noble gas, is monoatomic.
Have students recognise that noble gases exist in the monoatomic state.
They exist in nature as single atoms.

5. 6.1 The Stable Electronic Configuration of a Noble Gas
What is the Noble Gas Structure?
Noble gases have full or complete outer shells.
Helium has a duplet configuration
(2 outer electrons).
State that noble gases are inert, i.e. their atoms do not combine with other atoms. Have students understand that the 8 electrons in the outer shell (2 in the case of helium) makes the atoms stable and, therefore, inert. A duplet or octet configuration is also known as a noble gas configuration.
Ask students why atoms of other elements react with one another. Lead them to understand that atoms of other elements react in order to achieve the stable noble gas structure.
All other noble gases have an octet configuration
(8 outer electrons). 5

6. 6.1 The Stable Electronic Configuration of a Noble Gas
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. 6

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

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

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

10. No. of electrons ≠ No. of protons
6.2 Forming Ions
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.
Define Ions as charged particles formed when atoms lose or gain electrons.
No. of electrons ≠ No. of protons 10

11. 6.2 Forming Ions What is an Ion?
Ions can be positively- or negatively-charged.
Positively-charged ions are called cations.
Negatively-charged ions are called anions.
Some students may have the misconception that when an ion gains an electron, it becomes positive and vice versa. Highlight to them that electrons are negatively charged, so when an atom gains an electron, a negative ion is formed.
Clicking on the URL button will link you to < a website with an interactive animation introducing the formation of ions and ionic bonds. (The video is approximately 3.5 minutes long.)
URL 11

12. 6.2 Forming Ions Formation of Cations
Atoms of metals lose electrons to form positively-charged ions called cations.
In this way, they achieve the noble gas
configuration.
Mention that cations have a stable octet configuration in their outer shells. 12

13. 6.2 Forming Ions Example 1: Formation of sodium (Na+) ion Na atom
Electronic configuration: 2, 8, 1
Number of protons = 11
Number of electrons = 11
The Na atom loses one outer electron to form the Na+ ion. Why?
Ask students to identify the noble gas configuration achieved by the sodium ion in its outer shell.
To achieve stable octet (noble gas) configuration.
Neon (2, 8)

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

15. calcium atom loses two outer electrons
6.2 Forming Ions
Example 2: Formation of calcium (Ca2+) ion
2, 8, 8
2, 8, 8, 2
calcium atom loses two outer electrons 2+
Ca atom: 20p, 20n, 20e
Ca2+ ion: 20p, 20n, 18e
Charge = 20p + 20e
Charge = 20p + 18e
= 20(+1) + 20(–1)
= 20(+1) + 18(–1)
= (+20) + (–20) = 0
= (+20) + (–18) = +2
Neutral
Ca atom
Positively-charged
Ca2+ ion

16. 6.2 Forming Ions Common Cations and Their Charges Metal Ion
Formula of ion
sodium
sodium ion
Na+
potassium
potassium ion K+
calcium
calcium ion
Ca2+
magnesium
magnesium ion
Mg2+
aluminium
aluminium ion
Al3+
Ask students if they can identify the noble gas configuration of each ion, i.e. sodium ion has neon’s electronic configuration, calcium ion has argon’s electronic configuration.
Highlight to students that although the ions have the same electronic configuration as noble gases, they are not the same. For example, although sodium ion has the same configuration (2, 8) as neon, they are not identical particles because sodium ion has 11 protons, whereas neon has 10 protons.

17. 6.2 Forming Ions 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.
Mention that anions have a stable octet configuration in their outer shells. 17

18. 6.2 Forming Ions Example 1: Formation of chloride (Cl–) ion Cl atom
Electronic configuration: 2, 8, 7
Number of protons = 17
Number of electrons = 17
What happens in the formation of a chloride ion?
Ask students to identify the noble gas electronic configuration achieved by the chloride ion in its outer shell.
Emphasise that chlorine forms a chloride ion, not a chlorine ion.
The chlorine atom gains one electron in its outer shell to achieve a stable octet (noble gas) configuration.
Argon (2, 8, 8)

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

20. oxygen atom gains two electrons
6.2 Forming Ions
Example 2: Formation of oxide (O2–) ion
2, 6
2, 8
oxygen atom gains two electrons 2–
O atom: 8p, 8n, 8e
O2– ion: 8p, 8n, 10e
Charge = 8p + 8e
Charge = 8p + 10e
= (+8) + (–8)
= 0
= (+8) + (–10)
= –2
Neutral
O atom
Negatively charged
O2– ion

21. 6.2 Forming Ions Non-metal Ion Formula of ion chlorine chloride ion
Common Anions and Their Charges
Non-metal
Ion
Formula of ion
chlorine
chloride ion
Cl–
bromine
bromide ion
Br–
oxygen
oxide ion
O2–
sulfur
sulfide ion
S2–
Ask students if they can identify the noble gas configuration of each ion, e.g. chloride ion has argon’s electronic configuration.

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

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

24. 6.3 Ionic Bond: Transferring Electrons
Learning Outcome
At the end of this section, you should be able to:
describe how an ionic bonds are formed between metals and non-metals. 24

25. 6.3 Ionic Bond: Transferring Electrons
Ionic Bonding
Ionic bonds are formed between metals and non-metals.
Examples:
Group VII: Fluorine, chlorine
Group VI: Oxygen, sulfur
Examples:
Group I: Sodium, potassium
Group II: Magnesium, calcium
This is done through the transfer of electron(s) from metals to non-metals.

26. 6.3 Ionic Bond: Transferring Electrons
Ionic Bonding
Metallic atom
Non-metallic atom
loses electron(s)
gains electron(s)
Positive ion
(cation)
Negative ion
(anion)
Ask students:
What is another name for positive ions?
What is another name for negative ions?
Get students to recall that a metallic atom loses electron(s) to form a positive ion while a non-metallic atom gains electron(s) to form a negative ion. The oppositely charged ions are then held together by strong electrostatic forces of attraction.
Recap: Why do atoms form ions?
Answer: To achieve stable noble gas electronic configuration
electrostatic forces of attraction
(hold oppositely charged ions together) 26

27. 6.3 Ionic Bond: Transferring Electrons
Formation of Ionic Compound
Example 1: Sodium chloride
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−
Get students to identify the metal and non-metal elements in sodium chloride. Sodium is the metal, chlorine is the non-metal.
2, 8, 1
2, 8 27

28. 6.3 Ionic Bond: Transferring Electrons
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
+ e−
Cl –
2, 8, 7
2, 8, 8

29. Electrostatic forces of attraction
6.3 Ionic Bond: Transferring Electrons
Step 3: Formation of Ionic Bonds
Electrostatic forces of attraction
Loses one electron
Gains one electron
Sodium atom
2, 8, 1
Chlorine atom
2, 8, 7
Sodium ion
2, 8
Chloride ion
2, 8, 8
Clicking on the URL button will link you to < a website with a video on chemical bonding. The first part of the video (up till 0.51 seconds) can be used to demonstrate ionic bonding. The second part of the video (0.52 seconds onwards) may be used to demonstrate covalent bonding.
Alternative resource:
Go to < a website with an animation on ionic bonding of sodium chloride, magnesium oxide and calcium chloride.
Sodium and chlorine react in the ratio of 1 : 1 to form sodium chloride (NaCl).
URL

30. Magnesium atom loses two electrons.
6.3 Ionic Bond: Transferring Electrons
Example 2: Magnesium chloride
Magnesium atom loses two electrons.
Chlorine atoms
gain one electron each.
Chloride ion
2, 8, 8
Magnesium ion
2, 8
Chloride ion
2, 8, 8
Magnesium reacts with chlorine in the ratio of 1 : 2 to form magnesium chloride (MgCl2). 30

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

32. 6.4 Chemical Formulae of Ionic Compounds
Learning Outcome
At the end of this section, you should be able to:
deduce the chemical formula of an ionic compound from the charges on the ions and vice versa. 32

33. 6.4 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.
Explain that although ions are charged particles, the compounds they form are neutral. Thus, we can infer that the positive and negative charges must be balanced.

34. 6.4 Chemical Formulae of Ionic Compounds
Example: Magnesium oxide
Oxygen forms O2− ions.
Magnesium forms Mg2+ ions.
Mg2+
O2−
Charge: +2
Charge: −2
When writing chemical formulae of ionic compounds, the metal is usually written first.
When there is only 1 of each ion, the subscript ‘1’ is not written. E.g. MgO and not Mg1O1
Since 1 × (+2 charge) balances out 1 × (−2 charge),
The formula is MgO.

35. 6.4 Chemical Formulae of Ionic Compounds
Example: Copper(II) hydroxide
Copper ion
Hydroxide ion
Cu2+
OH−
Charge: +2
Charge: −1
To balance the charges, multiply the smaller charge (−1) by 2 to make it equal to +2.
Highlight to students that polyatomic ions need to be enclosed within brackets when there is a subscript (in the case where there is more than one polyatomic ion).
Since 1 × (+2 charge) balances out 2 × (−1 charge),
The formula is Cu(OH)2.

36. 6.4 Chemical Formulae of Ionic Compounds
Example 1
Write the chemical formula of aluminium oxide.
aluminium ion
oxide ion
Al 3 +
O 2 −
Charge: +3
Charge: −2
Al2O3
Therefore, the formula is Al2O3.

37. 6.4 Chemical Formulae of Ionic Compounds
Example 2
Write the chemical formula of calcium carbonate.
calcium ion
carbonate ion
Ca 2 +
CO3 2 −
Charge: +3
Charge: −2
Usually, the simplest set of whole numbers is written, e.g. CaCO3 and not Ca2(CO3)2. However, there are exceptions, e.g. H2O2 and N2O4.
Clicking on the URL button will link you to < a website with an interactive game on ionic bonding. Students will get to match different ions to form compounds and see how well they score. (Note: There is an error in the description of aluminium phosphate – its chemical formula should be AlPO4, not AlPO2.)
Ca2(CO3)2
CaCO3
Since ‘2’ is a common factor, it can be removed.
Therefore, the formula is CaCO3.
URL

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

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

40. 6.5 Structure and Physical Properties of Ionic Compounds
Structure of Ionic Compounds
Ionic compounds form giant ionic structures.
Also known as giant lattice structures or crystal lattices
Consist of an endlessly repeating three-dimensional lattice of positive and negative ions
The giant ionic structure is held together very tightly due to the strong electrostatic forces between the oppositely charged ions.
Ions are closely packed, arranged in an orderly manner and held in place by ionic bonds 40

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

42. 6.5 Structure and Physical Properties of Ionic Compounds
Structure of NaCl
Na+
Cl–
Strong forces of attraction between ions in crystal lattice
A large amount of energy is required to overcome these forces of attraction between ions. 42

43. 6.5 Structure and Physical Properties of Ionic Compounds
Structure of NaCl
Cl− ion
Each chloride ion is surrounded by six sodium ions.
Na+ ion
Each sodium ion is surrounded by six chloride ions.
Another representation of the 3-D arrangement of Na+ and Cl− ions
The ratio of sodium ions to chloride ions is 1 : 1.
Hence, the formula unit of sodium chloride is NaCl. 43

44. 6.5 Structure and Physical Properties of Ionic Compounds
Melting and Boiling Points of Ionic Compounds
Na+
Cl–
High melting and boiling points
Non-volatile
Exist as solids at room temperature
Ionic compounds have a giant lattice structure, which is held very tightly by strong attractive forces. A large amount of energy is required to overcome these forces to change an ionic compound from the solid state to the liquid state. Therefore, ionic compounds have high melting and boiling points and are solids at r.t.p. 44

45. 6.5 Structure and Physical Properties of Ionic Compounds
Solubility of Ionic Compounds
Usually soluble in water
Na+
Cl–
Cl–
Na+
dissolve in water
Water molecules
Clicking on the URL button will link you to < a website with a video simulation on how water molecules “pull” the positive and negative ions in an ionic compound away from each other.
Usually insoluble in organic solvents E.g. ethanol, turpentine, petrol
URL

46. 6.5 Structure and Physical Properties of Ionic Compounds
Electrical Conductivity of Ionic Compounds
solid NaCl
aqueous NaCl
molten NaCl
Sodium chloride does not conduct electricity in the solid state, but it can conduct in the molten and aqueous states.

47. 6.5 Structure and Physical Properties of Ionic Compounds
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.
A salt in the solid state, as shown earlier, has its ions held rigidly in fixed positions. It does not conduct electricity simply because the ions cannot move around. However, if we take the salt and dissolve it in water, the water molecules will pull the positive and negative ions away from each other. As a result, the ions will be free to move around to conduct electricity. Similarly, in the molten state, the ions will overcome some of the attractive forces between them and be free to move around. The presence of mobile ions enables electricity to be conducted. 47

48. Chapter 6 Ionic Bonding
Concept Map