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Exercise (Module: Atoms and Molecules) IJSO Training: Atoms and Molecules Exercise 1. Give 2 examples for each of the following: (a) Elements (b) Compounds (c) Ionic compounds with monoatomic ions only (d) Ionic compounds with polyatomic ions (e) Covalent compounds (f) Compounds capable of forming hydrogen bond (g) Gaseous elements (h) Liquid elements (i) Elements that form stable ions of +1 charge (j) Elements that form stable ions of +2 charge (k) Elements that form stable ions of ­1 charge (l) Elements that form stable ions of ­2 charge (m) Elements that form stable monoatomic molecules (n) Elements that form stable diatomic molecules 2. Which of the following is/are good conductor(s) of electricity at room temperature? (a) Aluminium (b) Iodine (c) Phosphorus (d) Sulphur (e) Carbon (graphite) (f) Mercury (g) Sodium chloride 3. Which of the following is/are good conductor(s) of electricity in molten state? (a) Calcium (b) Sodium chloride (c) Sugar (d) Iodine (e) Sulphur (f) Lead bromide
Exercise (Module: Atoms and Molecules) 4. Which of the following has/have similar chemical properties as sodium? (a) Magnesium (b) Cesium (c) Lithium (d) Hydrogen (e) Calcium 5. Which element has the largest atomic radius? (a) Na (b) Mg (c) K (d) Al 6. Which element has the highest melting point? (a) Sodium (b) Magnesium (c) Potassium (d) Calcium 7. Which element is hardest? (a) Phosphorus (b) Sodium (c) Magnesium (d) Chromium 8. Who proposed the Plum Pudding Atomic Model? (a) John Dalton (b) J. J. Thomson (c) D. I. Mendeleev (d) E. Rutherford
Exercise (Module: Atoms and Molecules) 9. Magnesium has three stable isotopes, 24 Mg, 25 Mg and 26 Mg. Their atomic masses and natural abundances are shown below. Calculate the relative atomic mass of magnesium. Isotope Atomic mass (au) Natural abundance (%) 24 23.9850 78.99 25 24.9858 10.00 26 25.9826 11.01 Mg Mg Mg 10. Strontium has four stable isotopes, 84 Sr, 86 Sr, 87 Sr, and 88 Sr. Their atomic masses and natural abundances are shown below. Calculate the relative atomic mass of strontium. Isotope Atomic mass (au) Natural abundance (%) 84 83.9134 0.56 86 85.9093 9.86 87 86.9089 7.00 88 87.9056 82.58 Sr Sr Sr Sr 11. Give the numbers of protons, neutrons and electrons that present in the following species. Species 24 No. of protons No. of neutrons No. of electrons 2+ (a) Mg (b) 37 Cl ­ (c) 40 Ca 2+ (d) CO3 2­ (e) SO4 2­ Consider the most abundant isotopes for item (d) and (e) 12. An element forms stable 2+ ions that have the same electron configuration as argon. What is the element? 13. Give the electron arrangements of the following elements: (a) Chlorine (atomic number 17) (b) Calcium (atomic number 20) (c) Nickel (atomic number 28) (d) Zinc (atomic number 30) (e) Arsenic (atomic number 33) (f) Bromine (atomic number 35)
Exercise (Module: Atoms and Molecules) 14. Balance the following chemical equations: (a) Pb(NO3)2 + NaCl à PbCl2 + NaNO3 (b) C2H5OH + O2 à H2O + CO2 (c) CCl4 + SbF3 à CCl2 F2 + SbCl3 (Advanced exercises – balancing redox reaction – the total charges on both sides must also be balanced) (d) MnO4 ­ + Fe 2+ + H + à Mn 2+ + Fe 3+ + H2O (e) MnO4 ­ + C2O4 ­ + H + à Mn 2+ + CO2 + H2O 15. Calculate the volume of CO2 produced from burring 14 mL of C2H5OH (ethanol). Assume the gas volume was measured at 25 o C and 1 atm. (Ethanol: density = 0.789 g cm ­3 , MW = 46.0688) 16. How many oxygen atoms are present in 12.5 g of calcium carbonate? 17. What is the mass of H2O produced from the combustion of 15 g of CH4? 18. Calculate the volume of CO2 produced from the combustion of 1.000 kg of gasoline? (assuming that the gasoline is composed of 100% octane – C8H18, and the gas volume is measured at 25 o C and 1 atm) 19. What is the volume of CO2 produced from the reaction of 4.5 g of CaCO3 with excess acid? Assume the gas volume was measured at 25 o C and 1 atm. 20. What is the volume of H2 produced from the reaction of 2.4 g of sodium metal with water? Assume the gas volume was measured at 25 o C and 1 atm.
Exercise (Module: Atoms and Molecules) 21. Shown below is the chemical structure of a common drug – aspirin. Give the number of: O OH C O HC HC O C C CH CH 3 C H (a)
(b)
(c) (d) (e) (f) (g) σ bonds π bonds sp 3 hybridized atoms sp 2 hybridized atoms lone­pair electrons carbon atoms having the trigonal planar geometry atoms having the tetrahedral geometry 22. Which of the following compounds has sp hybridized carbon atom? (a) H2C=CH2 (b) H2C=O (c) CO2 (d) CH4 23. Briefly explain why BF3 has a trigonal planar structure while BF4 ­ has a tetrahedral structure. (hint: consider the hybridization of the boron atom) 24. Which of the following compounds has the shortest C­H bond? (a) CH4 (b) H2C=CH2 (c) HC≣CH (d) H2C=O 25. Which of the following elements forms coloured ions? (a) Aluminium (b) Nickel (c) Cesium (d) Lead
Exercise (Module: Atoms and Molecules) 26. Which element has the highest electronegativity? (a) Fluorine (b) Oxygen (c) Bromine (d) Nitrogen 27. Which of the following type of intermolecular interactions are present in ammonia? (a) hydrogen bonding (b) dipole dipole interaction (c) ion dipole interaction (d) induced­dipole induced­dipole interaction. ­­­­ The End ­­­­