CHAPTER 5 CHEMICAL BONDS Almost all chemical substances exist as compounds in nature except inert gases and other stable element (such as gold and silver). Atom of other element that have less than eight valence electron are not stable Less stable atom will tend to release, accept or share electron to achieve the stable electron arrangement All other elements combine together to achieve the stability by forming duplet or octet electron arrangement by i) The transfer of electron ii) Sharing of electron Two types of chemical bonds formed:- i) ionic bonds ii) covalent bond Ionic Bond Covalent Bond 79
Ionic Bond Ionic bond formed when metal atom transfer electrons to non-metal atom to form ionic compound. Formation of Cation Formation of Anion Example: Draw the formation of sodium ion. Metal atom from group 1,2 and 13 tend to released all their valence electrons. Non-Metal atom from group 15, 16 and 17 tend to accept the electrons. 80
Exercise 1. Draw the formation of the following cations: a) Potassium ion b) Magnesium ion c) Aluminium ion 81
2. Draw the formation of the following anions: a) Chloride ion b) Oxide ion c) Nitride ion 82
Formation of Ionic Compound [Write in general about the formation of ionic compound] Example: Formation of Sodium Chloride, NaCl 83
Exercise 1. Explain the formation of ionic compound below: a) Lithium fluoride b) Magnesium oxide 84
c) Calcium chloride d) Aluminium oxide 85
2. Draw the formation of the following ionic compound: a) Lithium fluoride b) Magnesium oxide 86
c) Calcium chloride d) Aluminium oxide 87
Ionic Equations Equation that represent the formation of ionic compounds are known as ionic equation. Example: a) Formation of sodium chloride, NaCl i) Chemical Equation : ii) Half-ionic Equation : b) Formation of Magnesium oxide, MgO i) Chemical Equation : ii) Half-ionic Equation : Exercise 1. Write an ionic equation of the following compound a) Lithium fluoride b) Magnesium chloride c) Aluminium oxide 88
Exercise 1. Atom X and Y each have proton numbers of 3 and 8. What is the ionic compound formula formed between atoms X and Y? 2. Complete each of the following table: Atom Proton Number Electron Arrangement Ionic Formula Atom Proton Number Electron Arrangement Ionic Formula Compound Formula A 3 B 9 1 C 11 D 8 2 E 12 F 17 3 G 20 H 9 4 I 19 J 17 5 K 13 L 8 6 M 13 N 17 89
Covalent Bond Covalent bond is the chemical bond formed through the sharing of electron between two or more non metal atom to form covalent compound. Three types of covalent bonds: single covalent bond ( sharing one pair of e ) double covalent bond ( sharing two pairs of e ) triple covalent bond ( sharing three pairs of e ) Single Covalent Bond Example: Draw the formation of chlorine gas. 90
Double Covalent Bond Example: Draw the formation of oxygen gas. Triple Covalent Bond Example: Draw the formation of nitrogen gas. 91
Exercise 1. Draw the formation of the following compound. a) water b) Carbon dioxide 92
c) Ammonia b) Tetrachloromethane, CCl4. 93
Determine the Formula of Covalent Compound Guideline: 1. State the electron configuration of atoms. - Make sure electron valence for both atoms is either 4, 5, 6, and 7. 2. Determine the number of electrons needed to achieve stability. 3. Write the number of electron needed to achieve stability at the below right corner of each atom. 4. Cross the number. Example: If atom P has 8 protons and atom Q has 9 protons, determine the formula of the covalent compound formed. 94
Exercise 1. Atoms K and S each have a proton number of 6 and 8 respectively. What is the formula of the covalent compound which is formed by K and S? 2. Complete the table below to show the formulae of compounds which are formed. Atom Proton number Electron config. Atom Proton number Electron config. Compound formula A 6 2.4 B 9 2.7 AB4 C 6 D 16 E 7 F 1 G 1 H 8 I 6 J 17 K 6 L 8 95
Comparison between the formation of the ionic bond and the covalent bond IONIC BOND COVALENT BOND Similarity Differences Formation Particles Force of Attraction 96
The following figure compares and contrasts the properties of ionic compound and covalent compound IONIC COMPOUND COVALENT COMPOUND PROPERTIES Melting & Boiling point Electric Conductivity Physical State Solubility 97
Exercise 1. (a) Table 1.1 shows the proton number of three elements, X, Y, and Z. The letters used do not represent the actual symbols of the elements. Element Proton Number X 6 Y 12 Z 17 Table 1.1 i) Write the electron arrangement of: Atom Y : The ion of Z : ii) Write the formula of the compound formed between elements Y and Z. iii) Element X reacts with element Z to form a covalent compound with a formula XZ4. State two physical properties of this compound. i) Draw the electronic structure of the compound XZ4. 98
(b) Table 1.2 shows some physical properties of two compounds, U and V. Compound Melting pt ( o C) Boiling pt ( o C) Solubility in water Solubility in organic solvent U 800 1 420 Soluble Insoluble V - 95 86 Insoluble Soluble Table 1.2 i) State the physical state of the following compound at room condition. U : V : ii) State the type of compound for U. iii) Explain why melting point and boiling point of compound U is higher than V? 99