General Chemistry Exam 2/3 Chem 210 Section 02, Fall 2017

Transcription

1 General Chemistry Exam 2/3 Chem 210 Section 02, Fall 2017 Exam Information Aggregation of exams 2/3 to cover current material Complete your answers legibly in the space provided and show your work. Full credit will only be given for problems that demonstrate how the question was solved. Remember, most calculations are not considered complete unless they have the correct number of significant figures and units. You may only use a simple scientific calculation (no graphing or programmable calculators), and all book materials must be put away. This information may be helpful on the exam: Unit conversions and constants: 7 days = 1 week lb = kg 1 cal = J 1 ft = cm 1 ton = 2000 lb k = 2.31 x J pm 1 ml = 1 cm 3 1 atm = psi 1 atm = torr 1 amu = x g 4 cups = liters Avogadro s number, N A = x mol -1 Speed of light, c = x 10 8 m s -1 Plank s constant, h = x J s Example conversion: converting x meters to femtometers Useful equations: c = f = E photon = hf = h -V = IE = E photon KE a V a N a - p a B a V SI Prefixes: E R p a = EN a / (EN a + EN b ) f femto p pico n nano 10-9 m Micro 10-6 m milli 10-3 c centi 10-2 d deci 10-1 da deca 10 h hector 10 2 k kilo 10 3 M mega 10 6 G giga 10 9 T tera Feel free to remove this page from the exam packet while working. Page 1 of 7

2 Student Name: 1. The charges and sizes of the ions in an ionic compound affect the strength of the electrostatic attraction holding that compound together. Based on ion charges and relative ion size, rank the following compounds by their expected melting points: KF, CaO, CaF2, RbBr 2. In the space provided, briefly describe how does bond order relate to bond length and bond strength? Page 2 of 7

3 3. For the following molecules (a) Provide the best Lewis structure, include resonance and formal charges where necessary (b) Name the electronic geometry of the molecule (c) Give the approximate bonds angles, and the expected hybridization of the central atom (d) Indicate whether or not the molecule is polar, and if so the direction of the molecular dipole (Hint: it may be helpful to sketch the 3-dimension structure to help determine the dipole moment) CCl4 H3O + PH3 XeO4 CO3 2- Page 3 of 7

4 4. Consider the single bonds C-O, C-S, H-S, and C-Cl. Which of these single bonds will have the highest ionic character, and why? 5. In the space below, briefly explain why the radius of a Mg 2+ ion (0.065 nm) is smaller than the radius of a S 2- ion (0.184 nm) even though Mg atoms are much larger than S atoms. 6. Write electron configurations (you may use noble gas core notation) for each of the following atoms or ions. a. N b. Cd c. Fe d. Fe 2+ e. S 2- Page 4 of 7

5 7. a. What values can the quantum number have if the principle quantum number n=3? b. If =1, what values can m have? 8. Indicate if the following atoms or ions are paramagnetic or diamagnetic: a. H b. He c. F - d. Ca e. Cr How many sigma and pi bonds are there in a 1-butyne (ethylacetylene) molecule? Page 5 of 7

6 10. List the following molecules in order of least to most polar bonds: CF4, NF3 and OF2 Explain your choices 11. Use Lewis structures and formal charge considerations to suggest that the structure of a hydrocyanic acid molecule is HCN rather than HNC. Page 6 of 7

7 12. Draw the addition and subtraction of two hydrogen 1s atomic orbitals to form bonding and antibonding molecular orbitals, and clearly label the molecular orbitals. Briefly describe the difference between the bonding and an antibonding molecular orbital? Bonus Question. You won't lose any points on the exam for not trying to answer this question, but you may earn up to 4 bonus points. Give the name or chemical formula for the following, one bonus point for each answered correctly: (a) copper (II) hydroxide (b) HNO3 (c) NaH2PO4 (d) zinc carbonate Question Total Bonus Points Score Page 7 of 7