Download CHE1031 Chapter 2 Practice Quiz Key

Vermont Tech CHE1031 CHE1031 Practice Quiz 2: Atoms, Isotopes, Ions & Molecules Atomic Theory of Matter 1. Which is NOT a postulate of Dalton’s atomic theory? a) Atoms are composed of protons, neutrons and electrons. ⇐ b) All atoms of an element are identical. c) Atoms of an element are not changed by chemical reaction. d) Compounds form when elements combine at a constant ratio. e) Elements are made up of tiny particles called atoms. 2. Methane and ethane are both made of only carbon and hydrogen. In methane there are 12.0 g of carbon for every 4.00 g of hydrogen, a 3:1 mass ratio. In ethane, there are 24.0 g of carbon for every 6.00 g of hydrogen, a 4:1 mass ratio. This is an example of: a) Law of constant composition b) Law of multiple proportions ⇐ c) Law of conservation of mass d) Law of conservation of matter e) Octaves Discovery of Atomic Structure 3. Which form of radiation has no mass? Gamma – energy only 4. What did Rutherford’s gold-­‐foil experiment: a) Prove? Atoms have a dense central nucleus of protons & neutrons b) Disprove? Thompson’s plum pudding model of the atom Modern View of Atomic Structure 5. What three physical forces act at the atomic level? Define each and be sure that your reader can see the differences between the forces. 1) EM force 2) Strong nuclear force 3) Weak nuclear force Atomic Numbers & Mass Numbers 6. How many protons, neutrons and electrons are there in an atom of polonium? Atomic number 84, atomic mass 209 So 84 protons & 84 electrons; neutrons = 209 – 84 = 125 1
Vermont Tech CHE1031 Isotopes & Average Atomic Weight 7. The element X has three isotopes whose masses and abundances are shown below. Calculate the average atomic mass of element X. isotope abundance (%) mass (amu) 15
17
X 28.60 15.33 X 13.30 17.26 16
X 58.10 18.11 Avg = (0.2860)(15.33) + (0.1330)(17.26) + (0.5810)(18.11) = 17.20 amu Periodic Table 8. Name three elements most similar to magnesium. Berylium, calcium and strontium 9. When samples are placed in a mass spectrometer they are bombarded with _________ to change the samples from ______________ to _____________ before they are accelerated through the instrument. Electrons, atoms or molecules, ions Molecules & Chemical Formulas 10. Write formulas for three molecular compounds whose empirical formula is CH3. C2H6, C3H9, C4H12 11. Give an example of a pair of molecules with the same empirical formula that are also an example of the law of multiple proportions. C2H4, C4H8 Ions & Charges 12. Non-­‐metals tend to ____________ electrons to form __________ charged __________. gain negatively anions 13. Show how the compound Na2O forms from two sodium atoms and a single oxygen atom. Show this formation in three steps and show valence electrons in each step: show all atoms; show how ions form by movement of electrons; show how ions are attracted to form a compound. • 2 Na atoms, each with a single ve-­‐ and 1 O atom with 6 ve-­‐ +1
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• Nas’ ve-­‐ move to oxygen creating atoms: Na with no ve-­‐ & O with 8 ve-­‐ • Oppositely charge ions are attracted by EM force to create the compound, or aggregate, Na2O 2
Vermont Tech CHE1031 Naming Chemicals 14. The formulas of some compounds are shown below. FOR EACH, identify it as an ionic, molecular or acidic compound AND name the compound. Type? Name? a) N3O5 molecular trinitrogen pentoxide b) AlBr3 ionic aluminum bromide c) H(NO2) acidic nitrous acid d) SO molecular sulfur monoxide e) Mo(SO4) ionic molybdenum (II) sulfate 15. Write formulas for these compounds: a) nickel (II) cynanide Ni(CN)2 b) sodium peroxide Na2O2 c) phosphoric acid H3(PO4) d) magnesium nitride Mg3N2 3