Chapter 2 Atoms, Molecules, and Ions

Transcription

1 Chapter 2 Atoms, Molecules, and Ions 1. Methane and ethane are both made up of carbon and hydrogen. In methane, there are 12.0 g of carbon for every 4.00 g of hydrogen, a ration of 3:1 by mass. In ethane, there are 24.0 g of carbon for every 6.00 g of hydrogen, a ratio of 4:1 by mass. This is a statement of the law of. (a). constant composition (b). multiple proportions (c). conservation of matter (d). conservation of mass (e). octaves Explanation: The Law of Multiple Proportions states that if 2 elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers. 2. Which statement below correctly describes the responses of alpha, beta, and gamma radiation to an electric field? (a). Both beta and gamma are deflected in the same direction, which alpha shows no response. (b). Both alpha and gamma are deflected in the same direction, while beta shows no response. (c). Both alpha and beta are deflected in the same direction, while gamma shows no response. (d). Alpha and beta are deflected in opposite directions, while gamma shows no response. (e). Only alpha is deflected, while beta and gamma show no response. Explanation: Alpha particles are positively charged and beta particles have negative charges. As a result of their opposite charges they are deflected in opposite directions. 3. and reside in the atomic nucleus. (a). Protons, electrons (b). Electrons, neutrons (c). Protons, neutrons (d). None of the above Explanation: Only protons and neutrons are in the nucleus, electrons are always outside the nucleus. Copyright 2006 Dr. Harshavardhan D. Bapat 1

2 pm is the same as Å. (a) (b). 20 (c). 200 (d) Explanation: One pm = 1 x m and 1 angstrom = 1x m. Thus 100 pm = 1 angstrom and hence 200 pm = 2.00 Å 5. The atomic number indicates. (a). the number of neutrons in a nucleus (b). the total number of neutrons and protons in a nucleus (c). the number protons or electrons in a neutral atom (d). the number of atoms in 1 g of an element Explanation: The atomic number not only indicates the number of protons but also the number of electrons in a neutral atom since the number of protons in a neutral atom = number of electrons. 6. Which pair of atoms constitutes a pair of isotopes of the same element? (a). (b). (c). (d). 14 6X X 12 6X 14 X 17 9X 17 8X 19 10X 19 9X Explanation: Isotopes of an element are atoms of the same element with same number of protons but different number of neutrons. Only choice (b) has 2 atoms of X with 6 protons and 8 and 6 neutrons respectively. 7. Elements in Group 8A are known as the. (a). chalcogens (b). alkali metals (c). noble gases (d). alkaline earth metals Copyright 2006 Dr. Harshavardhan D. Bapat 2

3 8. are found uncombined, as monatomic species in nature. (a). Halogens (b). Alkali metals (c). Noble gases (d). None of the above Explanation: Since these elements do not react with other elements they are known as noble gases. 9. When a metal and a nonmetal react, the tends to lose electrons and the tends to gain electrons. (a). metal, metal (b). metal, nonmetal (c). nonmetal, metal (d). None of the above, these elements share electrons. Explanation: The reaction between a metal and nonmetal is possible due to the loss of electrons by the metal (forming cations) and gain of electrons by the nonmetal (forming anions. 10. The empirical formula of a compound with molecules containing 12 carbon atoms, 14 hydrogen atoms, and 6 oxygen atoms is. (a). C 12 H 14 O 6 (b). C 2 H 4 O (c). CH 2 O (d). C 6 H 7 O 3 Explanation: The empirical formula is always the simplest possible whole number ratio between the atoms of the molecules. 11. typically form ions with a 2+ charge. (a). Transition metals (b). Halogens (c). Alkaline earth metals (d). Alkali metals Explanation: The alkaline earth metals are in group 2A of the periodic table and lose 2 electrons to form cations with 2 positive charges. Copyright 2006 Dr. Harshavardhan D. Bapat 3

4 12. Magnesium reacts with a certain element to form a compound with the general formula MgX. What would the most likely formula be for the compound formed between potassium and element X? (a). KX (b). K 2 X 2 (c). K 2 X 3 (d). KX 3 (e). None of the above Explanation: In the compound MgX, X must have 2 negative charges since Mg will always have 2 positive charges. The element K will always form an ion with 1 positive charge and hence the only combination of K and X could be K 2 X, which is not one of the options 13. The charge on the manganese in the salt MnF 3 is. (a). +1 (b). -1 (c). +3 (d). -2 Explanation: Since every F has one negative charge, the Mn can have only 3 positive charges. 14. Barium forms an ion with a charge of. (a). +1 (b). -2 (c) +3 (d). None of the above Explanation: Barium is in group 2A of the periodic table and forms ions with only 2 positive charges. 15. Aluminum forms an ion with a charge of. (a). +2 (b). -3 (c). +3 (d) Iodine forms an ion with a charge of. (a). -7 (b). +1 Copyright 2006 Dr. Harshavardhan D. Bapat 4

5 (c). -1 (d) Oxygen forms an ion with a charge of. (a). -1 (b). +2 (c). -3 (d) Predict the empirical formula of the ionic compound that forms from sodium and fluorine. (a). Na 3 F (b). Na 2 F (c). NaF 2 (d). None of the above 19. Predict the empirical formula of the ionic compound that forms from magnesium and oxygen. (a). Mg 2 O (b). MgO (c). MgO 2 (d). Mg 3 O The correct name for H 2 CO 3 is. (a). carbonous acid (b). dihydrogencarbonate (c). carbohydrate (d). carbonic acid 21. The correct name for H 2 SO 3 is. (a). sulfuric acid (b). dihydrogensulfite acid (c). hydrosulfuric acid (d). sulfurous acid 22. The correct name for HC1O 3 is. (a). hydrochloric acid (b). perchloric acid (c). chloric acid Copyright 2006 Dr. Harshavardhan D. Bapat 5

6 (d). None of the above 23. The correct name for HBrO 2 is. (a). bromic acid (b). hypobromous acid (c). hypobromic acid (d). bromous acid Explanation: For both questions 22 and 23 you must know these names, there is no other trick. 24. The correct name of the compound Na 3 N is. (a). sodium nitride (b). sodium azide (c). trisodium nitride (d) sodium (III) nitride Explanation: Since Na is in group IA, there is no need to indicate the number of sodium ions in this compound. 25. The correct formula for molybdenum(iv) hypochlorite is. (a). Mo(C1O 3 ) 4 (b). Mo(C1O 2 ) 4 (c). Mo(C1O) 4 (d). Mo(C1O 4 ) The ions Ca 2+ and PO 4 3- form a salt with the formula. (a). CaPO 4 (b). Ca 2 (PO 4 ) 3 (c). Ca 2 PO 4 (d). Ca 3 (PO 4 ) 2 Explanation: The least common multiple of 2 and 3 is 6. To be able to reach this number you need 3 Ca 2+ ions and only 2 phosphate ions. Copyright 2006 Dr. Harshavardhan D. Bapat 6

7 27. Which one of the following is not one of the postulates of Dalton s atomic theory? (a). Atoms are composed of protons, neutrons, and electrons. (b). All atoms of a given element are identical; the atoms of different elements are different and have different properties. (c). Atoms of an element are not changed into different types of atoms by chemical reactions: atoms are neither created nor destroyed in chemical reactions. (d).compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. Explanation: Dalton did not know about the existence of subatomic particles. 28. Consider the following selected postulates of Dalton s atomic theory: (i) Each element is composed of extremely small particles called atoms. (ii) Atoms are indivisible. (iii) Atoms of a given element are identical (iv) Atoms of different elements are different and have different properties. Which of the postulates is (are) no longer valid? (a). (i) and (ii) (b). (ii) only (c). (iii) only (d). (ii) and (iii) only Explanation: Atoms are divided into subatomic regions such as the nucleus and orbitals and while the existence of isotopes proves that not all atoms of an element are identical 29. Of the following, the smallest and lightest subatomic particle is the. (a). neutron (b). proton (c). electron (d). alpha particle 30. All atoms of a given element have the same. (a). mass (b). number of electrons and neutrons (c). number of neutrons (d). number of protons Copyright 2006 Dr. Harshavardhan D. Bapat 7

8 31. Which combination of protons, neutrons, and electrons is correct for the isotope of 63 copper, Cu? 29 (a). 29p +,34nº, 29e - (b). 29p +,29nº,63e - (c). 63p +,29nº,63e - (d). 34p +,29nº,34e Which isotope has 45 neutrons? (a). (b). (c) Kr 78 34Se Br 35 (d) Cl 33. Isotopes are atoms of the same element that have the same number of but differing number of. (a). protons, electrons (b). neutrons, protons (c). protons, neutrons (d). electrons, protons 34. Different isotopes of a particular element contain the same number of. (a). electrons (b). neutrons (c). protons and neutrons (d). protons, neutrons, and electrons 35. In the periodic table, the elements are arranged in. (a). alphabetical order (b). order of increasing atomic number (c). order of increasing metallic properties (d). order of increasing neutron content 36. Elements exhibit similar physical and chemical properties. (a). with similar chemical symbols (b). with similar atomic masses (c). in the same period of the periodic table (d). in the same group of the periodic table Copyright 2006 Dr. Harshavardhan D. Bapat 8

9 37. An element in the upper right corner of the periodic table. (a). is either a metal or metalloid (b). is definitely a metal (c). is definitely a non-metal (d). is either a metalloid or a non-metal 38. An element that appears in the lower left corner of a periodic table is. (a). either a metal or metalloid (b). definitely a metal (c). either a metalloid or a non-metal (d). definitely a non-metal 39. Which one of the following does not occur as diatomic molecules in elemental form? (a). oxygen (b). nitrogen (c). sulfur (d). hydrogen 40. A molecular formula always indicates. (a). how many of each atom are in a molecule (b). the simplest whole-number ratio of different atoms in a compound (c). which atoms are attached to which in a molecule (d). the isotope of each element in a compound 41. An empirical formula always indicates. (a). which atoms are attached to which in a molecule (b). how many of each atom are in a molecule (c). the simplest whole-number ratio of different atoms in a compound (d). the geometry of a molecule 42. The molecular formula of a compound is always the empirical formula. (a). more complex than (b). different from (c). a whole number multiple of (d). the same as Copyright 2006 Dr. Harshavardhan D. Bapat 9

10 43. There are protons, neutrons, and electrons in 131 I -. (a). 131, 53, and 54 (b). 131, 53 and 52 (c). 53, 78, and 54 (d). 53, 131, and 52 (e). 78, 53, and Which species has 48 electrons? (a) Sn +2 (b) Sn +4 (c) Cd +2 (d) Ga 45. Which pair of elements is most apt to form an ionic compound with each other? (a). calcium, sodium (b). barium, bromine (c). oxygen, fluorine (d). sulfur, fluorine Copyright 2006 Dr. Harshavardhan D. Bapat 10