Chemistry Past Paper PDF - G-10 P-I E (65)

Chemistry Chemical Bonds Intermolecular - bonds +...

Chemistry Chemical Bonds Intermolecular - bonds + Oδ δ + δ H - H + - + δ δ δ δ + H O H O + δ δ H H - -H δ H+ + O δ Oδ δ δ + δ + δ + O δ + - H Intermolecular bonds H H δ H Fig. 10.20 - Intermolecular bonds in water These intermolecular forces are not as strong as the covalent bonds between the oxygen atoms and the hydrogen atoms in a water molecule. Yet, these intermolecular forces impart many special properties to water. Because of these intermolecular forces, water exists as a liquid at room temperature. In case that there were no intermolecular forces among the water molecules, water is a gas at room temperature. Some special properties possessed by water due to attractive forces among the water molecule are as follows. y High boiling point y High specific heat capacity y Having a higher density than that of ice 10.5 Properties of Ionic and Covalent Compounds Activity 3 Examining the electrical conductivity of the solutions of ionic and covalent compounds Requirement: Four beakers, two carbon rods, two bulbs, two batteries (Six dry cells), conducting wires, a salt solution (common salt), sugar solution, copper sulphate solution, distilled water 183 For free distribution Chemistry Chemical Bonds Method: y Take four equal beakers and label them A, B, C, D. y Add salt solution to A, copper sulphate solution to B, sugar solution to C and distilled water to D. y Dip two carbon rods in each solution, complete the circuit as shown in fig. 10.21 and see whether the bulb lights. The carbon rods should be washed well before using in the other solution. Bulb Battery Insulators Carbon rod Beaker Solution Examining the electrical conductivity of the solution of ionic and covalent compound Fig. 10.21 The bulb lights in the circuits with common salt and copper sulphate solutions. It doesn’t light in the circuits with the sugar solution and distilled water. Common salt and copper sulphate are compounds with ionic bonds. Hence, aqueous solutions of ionic compounds conduct electricity. Sugar and water are covalent compounds. Electricity does not flow through them. Experiment shows that even common salt in the fused state conducts electricity. This confirms that electricity flows through ionic compounds in aqueous solution and fused state. However electricity does not flow through ionic compound in solid state. For free distribution 184 Chemistry Chemical Bonds Melting Points and Boiling Points of some Compounds Summary Table 10.5 Boiling point $ Compound Melting $ 0C 0 Bond type C Sodium chloride 801 1413 Ionic Potassium chloride 776 1500 Ionic Water 0 100 Covalent Ammonia -78 -33 Covalent Oxygen -218 -183 Covalent Ethyl alcohol -117 79 Covalent Calcium oxide 2580 2850 Ionic Sulphur dioxide -73 -10 Covalent From Table 10.5 it is clear that melting points and boiling points of ionic compound are relatively high. Mostly they exist as solids at room temperature. The above Table also affirms that the melting points and boiling points of covalent compounds are low. Generally they are liquids or gases at room temperature. Characteristics of Ionic Compounds y Ionic compounds are composed of oppositely charged (+ and -) ions. y Most of the compounds have a solid crystalline form at room temperature. y They have high melting points and boiling points. y They conduct electricity in the fused (molten) state and in aqueous solution. y Most of the ionic compounds are soluble in water. Characteristics of Covalent Compounds 01. They mostly exist as molecules composed of several atoms. 02. Most of the covalent compounds are in the liquid or gaseous state at room temperature. 03. Generally the melting points and boiling points of covalent compound are low (However the lattice compounds have high melting points and boiling points). 04. The aqueous solutions of covalent compounds do not conduct electricity. 05. Some covalent compounds are soluble in water. 185 For free distribution Chemistry Chemical Bonds n For further exploratio Collect information about the unique characteristics of water caused by the intermolecular forces. Summary For free distribution 186 Chemistry Chemical Bonds Exercises 01. Define an ion. 02. Write the electronic configurations of the following ions and illustrate them by diagrams. (a) Na+ (b) Mg2+ (c) O2- (d) N3- 03. What is meant by an ionic bond? 04. Illustrate by diagrams how the compound calcium oxide is formed. 05. Draw the dot and cross diagrams of the following molecules. (a) Chlorine (b) Oxygen (c) Water (d) Methane (e) Ammonia 06. What is meant by a covalent bond? 07. Give two properties of ionic compounds and covalent compounds. 08. Carbon is an element in Group IV. Why carbon has a high melting point and a high boiling point. 09. Explain scientifically why common salt is readily soluble in water. 10. Give reason to the existance of high boiling point, 100 0C to water though it is a covalent compound. 187 For free distribution Chemistry Chemical Bonds Technical terms Chemical bonds - ridhksl nkaOk - Cµ\õ¯Ú¨ ¤øn¨¦ Cation - legdhkh - PØÓ¯ß Anion - wekdhkh - AÚ¯ß Ionic bonds - whksl nkaOk - A¯ß ¤øn¨¦ Covalent bonds - iyixhqc nkaOk - £[RmkÁ¾¨¤øn¨¦ Polarity - O%eùh;dj - øÚÄzußø© Inter molecular bond - wka;¾ wKql n, - ‰»UTØÔøh Âø\ Hydrogen bond - yhsârcka nkaOk - Iuµ\ß ¤øn¨¦ For free distribution 188