Chapter 2
Atoms, Molecules, and Ions

 2.1 First, find the S:O ratio in each compound.

Substance 1: S:O mass ratio = (6.00 g S) / (5.99 g O) = 1.00
Substance 2: S:O mass ratio = (8.60 g S) / (12.88 g O) = 0.668

2.2 0.0002 in x

2.3 or approximately 40 times

2.4 has 34 protons, 34 electrons, and (75 S 34) = 41 neutrons.

2.5 has (35 S 17) = 18 neutrons. has (37 S 17) = 20 neutrons.

2.6 The element with 47 protons is Ag. The mass number is the sum of the protons and the neutrons, 47 + 62 = 109. The isotope symbol is .

2.7 atomic mass = (0.6917 x 62.94 amu) + (0.3083 x 64.93 amu) = 63.55 amu 

2.8 2.15 g x

 2.9 Figure (a) represents a mixture of two different types of molecules.
Figure (c) represents a pure compound composed of two different elements.
Figure (b) represents a diatomic element.

2.10 Figure (b) represents a collection of hydrogen peroxide (H₂O₂) molecules.

2.11

2.12 adrenaline, C₉H₁₃NO₃

2.13 (a) LiBr is composed of a metal (Li) and nonmetal (Br) and is ionic.
(b) SiCl₄ is composed of only nonmetals and is molecular.
(c) BF₃ is composed of only nonmetals and is molecular.
(d) CaO is composed of a metal (Ca) and nonmetal (O) and is ionic.

2.14 Figure (a) most likely represents an ionic compound because there are no discrete molecules, only a regular array of two different chemical species (ions). Figure (b) most likely represents a molecular compound because discrete molecules are present.

2.15 (a) HF is an acid. In water, HF dissociates to produce H⁺(aq).
(b) Ca(OH)₂ is a base. In water, Ca(OH)₂ dissociates to produce OH^-(aq).
(c) LiOH is a base. In water, LiOH dissociates to produce OH^-(aq).
(d) HCN is an acid. In water, HCN dissociates to produce H⁺(aq).

2.16 (a) CsF, cesium fluoride
(b) K₂O, potassium oxide
(c) CuO, copper(II) oxide
(d) BaS, barium sulfide
(e) BeBr₂, beryllium bromide

2.17 (a) vanadium(III) chloride, VCl₃
(b) manganese(IV) oxide, MnO₂
(c) copper(II) sulfide, CuS
(d) aluminum oxide, Al₂O₃

2.18 (a) NCl₃, nitrogen trichloride
(b) P₄O₆, tetraphosphorus hexoxide
(c) S₂F₂, disulfur difluoride

2.19 (a) disulfur dichloride, S₂Cl₂
(b) iodine monochloride, ICl
(c) nitrogen triiodide, NI₃

2.20 (a) Ca(ClO)₂, calcium hypochlorite
(b) Ag₂S₂O₃, silver(I) thiosulfate or silver thiosulfate
(c) NaH₂PO₄, sodium dihydrogen phosphate
(d) Sn(NO₃)₂, tin(II) nitrate
(e) Pb(CH₃CO₂), lead(IV) acetate

2.21 (a) lithium phosphate, Li₃PO₄
(b) magnesium hydrogen sulfate, Mg(HSO₄)₂
(c) manganese(II) nitrate, Mn(NO₃)₂ (d) chromium(III) sulfate, Cr₂(SO₄)₃

2.22 The ionic compound represented in the drawing has 2 anions per cation. The ionic compound is CaCl₂.

2.23 (a) HIO₄, periodic acid
(b) HBrO₂, bromous acid
(c) H₂CrO₄, chromic acid

2.24 A normal visual image results when light from the sun or other source reflects off an object, strikes the retina in our eye, and is converted into electrical signals that are processed by the brain. The image obtained with a scanning tunneling microscope, by contrast, is a three-dimensional, computer-generated data plot that uses tunneling current to mimic depth perception. The nature of the computer-generated image depends on the identity of the molecules or atoms on the surface, on the precision with which the probe tip is made, on how the data are manipulated, and on other experimental variables.

2.25 Drawing (a) depicts a collection of SO₂ molecules.

2.27 Figures (b) and (d) illustrate the law of multiple proportions. The mass ratio is 2.

2.38 (a)
This result is numerically equal to the atomic mass of H in grams.

(b)
This result is numerically equal to the atomic mass of O in grams.

2.46 The subscript giving the atomic number of an atom is often left off of an isotope symbol because one can readily look up the atomic number in the periodic table.

2.56 (0.199 x 10.0129 amu) + (0.801 x 11.009 31 amu) = 10.8 amu for B

2.67 (a) The formula of ammonia is NH_3.
(b) The ionic solid potassium chloride has the formula KCl.
(c) Cl^S is an anion.
(d) CH₄ is a neutral molecule.

2.73

2.76 HI(aq) ® H⁺(aq) + I^S(aq); the anion is I^S
H₃PO₄(aq) ® H⁺(aq) + H₂PO₄^S(aq); the predominant anion is H₂PO₄^S
H₂CO₃(aq) ® H⁺(aq) + HCO₃^S(aq); the predominant anion is HCO₃^S

2.82 (a) SO₃^2S
(b) PO₄^3S
(c) Zr⁴⁺
(d) CrO₄^2S
(e) CH₃CO₂^S
(f) S₂O₃^2S

2.89

number of C atoms =

time =

2.97 ; X = 12.0005 amu for ¹²C prior to 1961.

2.106 Molecular mass = (8 x 12.011 amu) + (9 x 1.0079 amu) + (1 x 14.0067 amu) + (2 x 15.9994 amu) = 151.165 amu

2.109 (a) Because X reacts by losing electrons, it is likely to be a metal.
(b) Because Y reacts by gaining electrons, it is likely to be a nonmetal.
(c) X₂Y₃
(d) X is likely to be in group 3A and Y is likely to be in group 6A.