Full Name: ________________ Date: ________________ SCH4U Structure & Properties Unit Test Multiple Choice (K/U) Identify the letter of the choice that best completes the statement or answers the question. ____ ____ ____ ____ ____ ____ ____ ____ ____ 1. The 3p atomic orbital has the shape of a. a sphere d. two perpendicular dumb-bells b. a torus e. an egg c. a dumb-bell 2. How does atomic radius change from left to right across a period of the Periodic Table? a. it tends to decrease b. it tends to increase c. it does not change d. it first increases, and then decreases e. it first decreases and then it increases 3. Why do energy levels exist in atoms? a. electrons are negatively charged b. electrons are attracted to certain numbers of neutrons c. electrons are able to possess any range of energy d. electrons will only display certain colours e. electrons are only able to possess quanta of energy 4. What was Planck's contribution to the quantum mechanical model of the atom? a. the uncertainty principle b. the concept of quanta of energy c. the idea that every mass has a wave with which it is associated d. the wave equation e. a relationship between energy and mass 5. What did Schrodinger contribute to the quantum mechanical model of the atom? a. the uncertainty principle b. concept of quanta of energy c. the idea that every mass has a wave with which it is associated d. the wave equation e. a relationship between energy and mass 6. Which of the following is the electron configuration for neon? a. 1s22s22p43s2 d. 1s32s32p4 1 1 6 2 b. 1s 2s 2p 3s e. 1s22s22p8 2 2 6 c. 1s 2s 2p 7. What made Rutherford believe that atoms are mostly empty space? a. most alpha particles went straight through the gold foil b. some alpha particles were deflected by the gold foil c. the line spectra of excited atoms d. atoms are electrically neutral e. none of the above 8. Bohr's model of the atom can be termed a "quantum" model of the atom because a. electrons and protons are equal b. it is based on the solar system c. the nucleus is positive d. each electron can possess only specific amounts of energy e. the potential energy of electrons is measurable 9. Which of the atoms could have the following valence electron configuration? s p a. b. c. carbon nitrogen boron d. e. sulfur none of the above 2 ____ 10. Which of the following is the configuration of carbon? a. 1s22s22p2 d. 1s22s12p4 2 2 4 b. 1s 2s 2p e. none of the above c. 1s22s12p3 ____ 11. Polar covalent bonds occur between a. atoms which both have equally high electronegativities b. atoms which have high but unequal electronegativities c. atoms which both have equally low electronegativities d. atoms which both have equally low ionization energies e. atoms which have low but unequal ionization energies ____ 12. Which of the molecules, CO2, H2O, NH3, and BF3, will be polar? a. CO2, NH3 and BF3 d. CO2, H2O and NH3 b. H2O and NH3 e. CO2 and BF3 c. H2O and BF3 ____ 13. Why does a central atom surrounded by 4 atoms have a tetrahedral shape instead of a square planar shape? a. orbitals are never at right angles to each other b. the lone pairs around the central atom push the 4 atoms into this configuration c. the angle in a tetrahedron is larger than in a square planar arrangement d. the 4 atoms want to be as close together as possible e. none of the above ____ 14. Which forces exist between iron, Fe, particles? I. Van der Waals II. metallic bonding III. hydrogen bonding IV. dipole a. I only d. I, III and IV only b. I and IV only e. I, II and III only c. I and II only ____ 15. Which statement is the best description of chlorine, Cl2? a. polar molecule d. ionic compound b. polar bonds, non polar molecule e. none of the above c. non polar molecule ____ 16. Which statement is the best description of potassium chloride, KCl? a. polar molecule d. ionic compound b. polar bonds, non polar molecule e. none of the above c. non polar molecule ____ 17. What type of substance is carbon dioxide, CO2? a. ionic d. metallic b. molecular e. none of the above c. covalent network ____ 18. What type of substance is hydrogen sulfide, H2S? a. ionic d. metallic b. molecular e. none of the above c. covalent network ____ 19. How will four pairs of electrons surrounding a central atom be arranged? a. pyramidally d. linearly b. spherically e. trigonally c. tetrahedrally 3 Short Answer (I/C) 20. Ionization energy tends to increase from left to right on the periodic table. There are two exceptions to that rule in the graph below. Explain them using Quantum Theory. (2 marks) 21. Draw and write the electron configuration for calcium. (2 marks) 22. Draw the electron configuration for oxygen and explain how you use Hund's Rule and the Pauli Exclusion principle to do it. (2 marks) 23. Why is sulfur able to bond with six different atoms at once? (2 marks) 24. Distinguish between single and double bonds with respect to the bonding orbitals. (2 marks) 25. Draw the electron configuration for Scandium, Sc. (2 marks) 26. What is meant by the term "orbital"? (2 marks) 4 27. Explain how VSEPR theory explains the shape of a central atom surrounded by two unbonded pairs of electrons and two other atoms. (2 marks) 28. Predict the shape of PF5. Indicate the bond angles. (2 marks) 29. Predict the shape and bond angle(s) of beryllium difluoride, BeF2. (2 marks) 30. Why do metals conduct electricity? (2 marks) Essay (MC) Answer only ONE of the following questions. (8 marks) 31. Explain water's properties using what you know about its inter- and intramolecular forces. 32. Explain VSEPR theory in your own words. Use examples. M.C. Short Ans. Essay K/U I, C MC _____ 19 *** _____ 22 _____ 8 *** marked by: (first & last name): __________________________ 5 4U-theory Answer Section MULTIPLE CHOICE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. ANS: C ANS: A ANS: E ANS: B ANS: D ANS: C ANS: A ANS: D ANS: D ANS: A ANS: B Atoms with unequal electronegativities will not share electrons equally, therefore one end of the bond ends up with a partial positive charge and the other ends up with a partial negative charge. Atoms with low electronegativities are metals, which do not bond covalently with each other. ANS: B ANS: C ANS: C ANS: C ANS: D ANS: B ANS: B ANS: C SHORT ANSWER 20. ANS: Magnesium has a full s orbital. Since full orbitals are more stable than partially filled orbitals, it is more difficult to remove that last electron. Aluminum has one electron in its p orbital. Since losing this electron would leave it with a full s orbital, this electron is easily removed. Similarly, if sulfur loses an electron, it is left with a half filled set of p orbitals, which is a relatively stable configuration. As a result, it is relatively easy to remove the electron from sulfur. Since phosphorus already has the half filled orbital configuration, it is difficult (relative to sulfur) to remove an electron from it. 21. ANS: 6 22. ANS: 1s22s22p4 23. 24. 25. 26. Pauli exclusion principle states that no two electrons can have the same four quantum numbers, therefore each orbital can hold only two electrons with opposite spins. Hund's rule says that the electrons in orbitals with the same energy are half filled first before more are added. Also, the electrons in those half filled orbitals must have the same spin. ANS: Sulfur's valence shell is the third energy level. The third energy level contains s, p and d orbitals but sulfur uses only the s and p orbitals for its own electrons. As a result, it can form coordinate bonds with more than four atoms by using its empty d orbitals. ANS: - In a single bond, there is direct overlap of two orbitals. - In a double bond, two orbitals directly overlap and two others overlap laterally. ANS: 3d 4s 3p 3s 2p 2s 1s ANS: volume of space in which there is a high probability of finding an electron 7 27. ANS: The two bonded pairs and two unbonded pairs of electrons around the central atom and then spread out in space so that they can be as far apart as possible. Thus, they form a tetrahedral shape. The shape of water(HO-H) ends up being bent. because the unbonded pairs of electrons are invisible. 28. ANS: The shape is trigonal bipyramidal with 120o on the horizontal plane and 90o along the vertical plane. 29. ANS: Linear with 180o bond angle. 30. ANS: The delocalized electrons are free to move from one place to another, thus forming an electric current. ESSAY 31. ANS: Water is a small covalent compound that is highly polar. It does not conduct electricity as it is not ionic and there are no delocalized electrons. The molecule is polar because the oxygen has two lone pairs of electrons. Thus, the shape is based on a tetrahedron and the molecule is bent. Since oxygen is so electronegative, the electrons spend more time with it than the hydrogens, and the molecule ends up being polar. The hydrogenseach with partial positive charges- are then attracted to the partially negative oxygens on other water molecules. This causes cohesion between water molecules, which means that is more difficult to change it to a gas. Thus, water has an extremely high boiling point compared to other molecules like it. Also, since it is able to absorb more energy before it changes state, it has a high heat capacity and is an excellent insulator. Its polarity allows it to cling to objects easily. 32. ANS: - Electrons repel; therefore, they will attempt to stay as far apart as possible in a molecule. To do this, bond angles must be maximized. - Lone pairs take up more room than bonded pairs and they repel more. - In methane, the carbon is surrounded by four hydrogen atoms. If the bonded pairs of electrons are to stay as far apart as possible in three-dimensions, they will be 109o apart. This produces a characteristic tetrahedral shape. If the molecule is like ammonia, though, with a lone pair and three atoms bonded to the central atom, the shape is still based on the tetrahedron, but, since the lone pair takes up more room, the bond angles for the N-H's will be smaller than 109o. However, the shape is named by the atoms only, therefore the shape would be trigonal pyramid. For five atoms surrounding a central atom, our choice in angles is limited by the orientation of orbitals in space. Thus, the angles are 90o and 120o instead of having all of the angles equal.