Chapter 2 Atoms, Molecules, and Ions. Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 2–2 QUESTION The early chemical pioneer

Chapter 2

Atoms, Molecules,Atoms, Molecules,and Ionsand Ions

Copyright © Houghton Mifflin Company. All rights reserved. CRS Question, 2–2

QUESTIONThe early chemical pioneer John Dalton proposed a set of descriptive principles summarizing specific knowledge about atoms. This became known as The Atomic Theory. One key point was “Chemical reactions involve reorganization of the atoms—changes in the way they are bound together.” Put that idea with the common phrase “you are what you eat.” Now, which of the following best describes the connection between eating pizza and John Dalton?


QUESTION (continued)1. Many of the components that make up pizza will soon become

part of your body, but you won’t look like a pizza because the components will be broken into new fragments and later reassembled differently.

2. Many of the components that make up pizza will soon become part of your cells, but you won’t actually look like a pizza because the atoms in pizza change identities when the pizza is digested.

3. The way the atoms in pizza are bound together is not affected by digestion—once inside you, the atoms in compounds remain connected. There are proteins, fats, and carbohydrates in pizza. The atoms in those compounds remain connected that way as they become part of your cells.


ANSWERChoice 1 explains that you are what you eat because the “what” is actually made up of atoms that are not destroyed during digestion. Many of the atoms in compounds that are found in pizza become rearranged with new connections and may become part of your cellular makeup.

Section 2.3: Dalton’s Atomic Theory


QUESTIONJohn Dalton was a strong proponent (and some maintain the originator) of the Law of Multiple Proportions. Of the following, which best explains why the law works?

1. In a series of compounds using the same atoms, each atom hasa whole number for its mass.

2. All atoms of a certain type have the same mass, therefore nofractions result when comparing masses from one compoundto the next.

3. Atoms are “whole” units therefore comparing atomic massesin a series of compounds will eventually reduce to wholenumbers.

4. I think I need to review the Law a bit more.


ANSWERChoice 3 explains the basis for the Law of Multiple Proportions (When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.) because the smallest unit of the compounds in any series will always contain whole atoms. These smallest units can be compared to each other, but each will have only whole atoms.

Section 2.2: Fundamental Chemical Laws


QUESTIONTwo common air pollutants when analyzed yield the following information; Compound I shows that 1 gram of sulfur combines with 1 gram of oxygen. Compound II shows that 1.5 grams of oxygen combines with 1 gram of sulfur. This is consistent with the law of multiple proportions because…

1. the analysis shows that sulfur and oxygen can combine inmore than one way.

2. the analysis shows that the combination of sulfur andoxygen is very close to 1 in both cases.

3. the analysis shows that a small whole number (2) couldbe used to make a ratio of 2:3 for the oxygen mass incompound I compared to compound II.


ANSWERChoice 3 offers the same conclusion as the actual Law of Multiple Proportions. If 1 and 1.5 are both multiplied by 2 the ratio is still maintained (1.5 to 1 is the same as 3:2 so multiplying by 2 does not change the ratio and does produce whole numbers for both).

Section 2.2: Fundamental Chemical Laws


QUESTIONJ.J. Thomson’s early work helped us understand that atoms could be divided into smaller parts such as electrons. A moving charged particle follows a curved path through a magnetic field. The curvature of the path through that field is most affected by the particle’s charge to mass ratio. Of the following, which would have the greater curvature through the same magnetic field?

1. An electron2. A proton3. A neutron4. I am not sure which would curve the most, a particle with

greater or with lesser charge to mass ratio?


ANSWER Choice 1 (the electron) would have the greater charge to mass ratio due to the extremely small mass and a –1 unit charge. Note the proton has a greater mass, with a +1 unit charge so it would have a smaller charge to mass ratio.

Section 2.4: Early Experiments to Characterize the Atom


QUESTION

Rutherford’s “Gold Foil” experiment helped shape what tenet of atomic theory? What aspect of the experiment led to this conclusion?


QUESTION (continued)

1. Electrons are embedded in atoms like “plums in a pudding”—most alpha particles go through the gold atoms.

2. Atoms must have a nucleus—only a very narrow beam of alpha particles could exit the lead box.

3. Atoms must have a nucleus—most, but not all, alphas encountered empty space inside of atoms.

4. Electrons are negative particles—only a few positive alpha particles backscattered because the negative electrons were able to neutralize them.


ANSWERChoice 3 describes the correct conclusion, for the correct reason. Since most alpha particles passed through the atom unaltered there must be mostly empty space. However, a few backscattered and calculations were able to point out that only a very small, very dense nucleus would produce those results.

Section 2.4: Early Experiments to Characterize the Atom


QUESTIONOf the following three choices, which would have the greatest number of neutrons?

1. 137Ba2+

2. 128Te2–

3. 133Cs


ANSWERChoice 1 would have 81 neutrons. The mass number – proton number = neutron number. Ionic charges have no influence on neutron number.

Section 2.5: The Modern View of Atomic Structure: An Introduction


QUESTIONOf the following, which would NOT qualify as an isotope of 35Cl?

1. 36Cl2. 35Cl–

3. 37Cl–

4. I am not sure what distinguishing feature qualifies two atomsto be called isotopes.


ANSWERChoice 2 is NOT an isotope of 35Cl. All three choices represent a form of chlorine but choice 2 has the same number of neutrons as the atom in the question, therefore it does not fit the criteria for isotopes (i.e. variable neutron number with constant proton number).

Section 2.5: The Modern View of Atomic Structure: An Introduction


QUESTIONCalcium plays several critical roles in the functioning of human cells. However, this form of calcium is the ion made with 20 protons and 18 electrons. Therefore the ion would be…

1. positive and called an anion.2. positive and called a cation.3. negative and called an anion.4. negative and called a cation.


ANSWERChoice 2 provides the correct relationship and name for an atom of calcium (20 protons = 20+) that has lost two electrons (now with 18–). The ion would have a +2 charge. Positive ions are called cations.

Section 2.6: Molecules and Ions


QUESTIONThe element found in the 6A family (or group 16) and period four can be toxic and a micronutrient. What is the symbol for that element?

1. Sb2. As3. Se4. Te


ANSWERChoice 3 pinpoints an element in both the 6A column and row four. Remember to include the first row of Hydrogen and Helium when counting rows.

Section 2.7: An Introduction to the Periodic Table


QUESTIONWhat element in the alkaline earth family has an atomic number that is the average of the element directly above and below it on the periodic table, and is in the fifth period?

1. Mg2. Na3. Rb4. Sr


ANSWERChoice 4 depicts an element in the fifth period, the alkaline family (group II), and with 38 protons Sr contains the average number of protons between 20 and 56.



QUESTIONFrom the following list select the element that is most likely to become an anion during a chemical reaction.

1. Hydrogen2. Tungsten3. Germanium4. Bromine


ANSWERChoice 4, Br, is the nonmetal found furthest to the right on the periodic table in the list. Nonmetals typically become negative when they react with other elements, a trend that generally increases from left to right.



QUESTIONOf the following which would not be considered a metalloid?

1. Ge2. Sb3. Se4. Did I miss something? What is a metalloid?


ANSWERChoice 3, Se, is the only element listed that is not on the “stairway” between metals and nonmetals, therefore it is the only non-metalloid listed.



QUESTIONOf the following, which is most likely to become a cation as a result of a chemical reaction? What would be the charge on that cation?

1. N; –32. Ne; +13. Na; +14. I don’t know how to make this type of prediction. Aren’t

there too many variables to tell?


ANSWERChoice 3 is correct because Na is a metal, which usually forms cations, and (as a member of column I) it’s common charge would be +1.



QUESTIONOf the following, which provides the most acceptable name for Fe2(C2O4)3?

1. Iron (II) oxalate2. Iron (II) oxalate (III)3. Iron (III) trioxalate4. Iron (III) oxalate


ANSWERChoice 4 is correct. Since iron can form compounds where it is commonly a +2 or +3, the roman numeral must be provided to indicate the charge (+3 in this case.) Since the iron charge is specified it is not necessary to indicate the number of oxalate ions present.

Section 2.8: Naming Simple Compounds


QUESTIONWhich of the following provides the correct name for Ca(H2PO4)2?

1. Calcium dihydrogen phosphate2. Calcium (II) hydrogen phosphate3. Calcium di-dihydrogen phosphate4. Calcium (II) dihydrogen phosphate


ANSWERChoice 1 provides the correct name for Ca(H2PO4)2. It is not necessary to use roman numerals when an atom typically only has one oxidation state (such as calcium’s +2.) Also, the anion combination only has one possibility here so it does not need a prefix Ca(H2PO4)2.



QUESTIONOf the following which provides the most acceptable name for Cr2O7

2–?

1. Dichromium heptoxide2. Dichromium heptoxide ion3. Chromium (VI) oxide 4. Dichromate ion


ANSWERChoice 4 is the name given to this polyatomic ion. When metals commonly exhibit more than one oxidation number, a roman numeral is used to specify the state in a compound. However, in this case using the roman numeral still leaves some ambiguity since CrO3 shows Cr in the +6 state as does Cr2O7

2–. Therefore, “dichromate” is used to assign a specific name to a specific arrangement.



QUESTIONWhat is the correct name for this compound? Na2O2

1. Disodium dioxide2. Sodium (I) peroxide3. Disodium peroxide4. Sodium peroxide


ANSWERChoice 4 is correct. Since sodium only has one charge (+1) in compounds there is no need to use a roman numeral to designate its charge. Merely naming the oxygen “peroxide” is sufficient. Since it always carries a –2 charge, there can only be one combination between +1 and –2 (two +1 charges are needed) so the name provided in choice 4 unambiguously describes the compound.



QUESTIONHypochlorous acid is related to the anion found in common household bleach. Which of the following is that common anion?

1. ClO4–

2. ClO3–

3. ClO2–

4. ClO–


ANSWERChoice 4 represents the hypochlorite ion, ClO–, that can be made to form hypochlorous acid HClO.


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Chapter 2 Atoms, Molecules, and Ions. Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 2–2 QUESTION The early chemical pioneer