Chapter 3

A student makes a compound of sulfur and oxygen. She uses \(5.00 \mathrm{~g}\) of sulfur and \(4.99 \mathrm{~g}\) of oxygen, and all of the elemental substances are completely used up. What is the percent sulfur in the compound?

A student makes two different compounds of nitrogen and oxygen using the masses shown below. In both cases, all of the elemental substances are completely used up. Compound \(1 \quad 10.0 \mathrm{~g}\) nitrogen \(+11.42 \mathrm{~g}\) oxygen Compound \(2 \quad 10.0 \mathrm{~g}\) nitrogen \(+22.84 \mathrm{~g}\) oxygen What is the percent oxygen in each compound?

A \(101.96-\mathrm{g}\) sample of a compound of aluminum and oxygen is \(47.1 \%\) by mass oxygen. (a) What is the percent by mass aluminum in this compound? (b) Of the \(101.96 \mathrm{~g}\) of this compound, how many grams are aluminum?

You visit France, where a local salesperson tries to sell you special water from a mountain spring. This water is supposed to be special because it has the formula \(\mathrm{H}_{3} \mathrm{O}\). What law does this claim violate?

When coal (essentially pure carbon) is burned, it combines with atmospheric oxygen to produce carbon dioxide gas. Nevertheless, when the coal burns, it seems to disappear. Why is this not a violation of the law of conservation of matter?

Using Dalton's ball-and-hook atomic model, sketch an explanation of how it is possible for hydrogen to combine with oxygen to form two different compounds- water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) and hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\).

Give the full atomic symbol for an atom that has 16 neutrons and an atomic number of 15 .

Bromine (Br) has two abundant isotopes, one with 44 neutrons and the other with 46 neutrons. Give the full atomic symbols for both isotopes.

Fill in this table: $$ \begin{array}{lcccc} & { }^{14} \mathrm{~N} & \frac{24}{12} \mathrm{Mg} & { }_{11}^{23} \mathrm{Na} & { }^{59} \mathrm{Fe} \\ \hline \text { Mass number } & ? & ? & ? & ? \\ \text { Atomic number } & ? & ? & ? & ? \\ \text { Number of protons } & ? & ? & ? & ? \\ \text { Number of neutrons } & ? & ? & ? & ? \\ \text { Number of electrons } & ? & ? & ? & ? \\ \hline \end{array} $$

What is the mass in grams of a billion billion \(\left(10^{18}\right)\) atoms of \({ }^{24} \mathrm{Mg}\) ? The atomic mass of \({ }^{24} \mathrm{Mg}\) is \(23.9850\) amu.

Chlorine exists as two isotopes in nature, \({ }_{1} 5 \mathrm{Cl}\) (atomic mass \(34.969 \mathrm{amu}\), abundance \(75.77 \%\) ) and \({ }_{17}^{37} \mathrm{Cl}\) (atomic mass \(36.966\) amu). (a) What is the percent abundance of the \({ }_{1}^{37} \mathrm{Cl}\) isotope? (b) Calculate the weighted average of the atomic mass of naturally occurring chlorine. (c) How many times more massive is \({ }_{1}^{37} \mathrm{Cl}\) than \({ }_{17}^{35} \mathrm{Cl}\) ?

How many groups constitute the representative (main-group) elements?

Does the stair-step boundary line that separates metals from nonmetals in the periodic table cross into the transition-metal portion of the table?

What do the elements in a group of the periodic table have in common with one another?

What are the period number and group number of the element that has atomic number \(15 ?\)

Which elements with atomic numbers greater than 40 can be expected to have chemical properties similar to those of the element bromine (Br)? What is the periodicity of these two elements?

What would the periodicity be if the transition metals, lanthanides, and actinides were removed from the periodic table?

Give the full symbol for the atom or ion that has 26 protons and 30 neutrons in its nucleus and 23 electrons outside its nucleus. Also give the number of the group this element is in.

Give the full symbol for the atom or ion that has eight protons and eight neutrons in its nucleus and ten electrons outside its nucleus. Also give the name of the group this element is in.

When wood burns, the mass of the ash is less than the mass of the original wood. Yet the law of conservation of matter says that mass cannot be created or destroyed in a chemical reaction. How do you reconcile the result of burning with this law?

Volcanoes spew off hydrogen sulfide, a poisonous, bad-smelling gas. A \(100.00-\mathrm{g}\) sample of hydrogen sulfide gas was obtained from some strange volcanic planet. Analysis showed that \(94.08 \mathrm{~g}\) of it is the element sulfur. The rest of the sample consists of the element hydrogen. (a) What are the percentages by mass of sulfur and hydrogen in this sample? (b) Hydrogen sulfide from Earth has exactly the same percent compositions for \(\mathrm{S}\) and \(\mathrm{H}\) as hydrogen sulfide from the strange volcanic planet. Which law accounts for this?

If a scientist during Dalton's time found that hydrogen sulfide always had the formula \(\mathrm{H}_{2} \mathrm{~S}\), how would this have been explained?

Two compounds of iodine (I) and chlorine (Cl) are analyzed. Compound A consists of \(126.9 \mathrm{~g}\) of \(\mathrm{I}\) and \(35.45 \mathrm{~g}\) of Cl. Compound B consists of \(126.9 \mathrm{~g}\) of I and \(106.4 \mathrm{~g}\) of \(\mathrm{Cl}\). (a) What is the percent composition of each element in compound A? (b) What is the percent composition of each element in compound \(\mathrm{B} ?\)

Suppose \(12.0 \mathrm{~g}\) of carbon \((\mathrm{C})\) reacts with \(70.0 \mathrm{~g}\) of sulfur (S) to give \(76.0 \mathrm{~g}\) of the compound carbon disulfide \(\left(\mathrm{CS}_{2}\right)\). In the process, all the carbon gets used up, but some elemental sulfur is left over. (a) For the law of conservation of matter to be obeyed, how much sulfur is unused? (b) What is the percent \(\mathrm{C}\) in \(\mathrm{CS}_{2} ?\) (c) What is the percent \(\mathrm{S}\) in \(\mathrm{CS}_{2} ?\) (d) What is the sum of the \(\% \mathrm{C}\) and \(\% \mathrm{~S}\) in \(\mathrm{CS}_{2} ?\)

Two different compounds, both consisting of sodium (Na) and oxygen (O), were analyzed. The data are given below: $$ \begin{array}{cccc} & \begin{array}{l} \text { Mass of } \\ \text { sample } \\ \text { Compound } \end{array} & \begin{array}{l} \text { Mass of } \\ \text { analyzed } \end{array} & \text { O present } & \begin{array}{l} \text { Mass of } \\ \text { Na present } \end{array} \\ \hline \mathrm{A} & 19.50 \mathrm{~g} & 8.00 \mathrm{~g} & ? \\ \mathrm{~B} & 61.98 \mathrm{~g} & 16.00 \mathrm{~g} & ? \\ \hline \end{array} $$ (a) Fill in the last column of the table. (b) Calculate the \(\% \mathrm{Na}\) and \(\% \mathrm{O}\) for both compounds.

Name the three subatomic particles found in an atom and give their relative masses and charges.

Given that the mass of an electron is \(5.486 \times 10^{-4}\) amu, and the mass of a proton is \(1.007\) amu, calculate how many times heavier a proton is than an electron.

In Rutherford's alpha-particle scattering experiment: (a) How did he interpret the observation that only a very few of the \(\alpha\) particles were scattered by the gold foil and most of them went straight through? (b) What was wrong with his model of the atom as far as the physics of the day was concerned?

Suppose all the alpha particles in Rutherford's experiment went straight through the gold foil with absolutely no deflections. What would this imply about the structure of the atom?

What else besides an atom's mass number would you need to determine its elemental identity? Explain how you would use it along with the mass number.

Does knowing how many electrons a neutral atom has tell you its elemental identity? Explain.

Physicists are fond of saying that an atom is mostly empty space. What justifies this statement?

Fill in the following table for four neutral atoms: $$ \begin{array}{lcccc} & { }_{8}^{15} \mathrm{O} & ? & ? & ? \\ \hline \text { Mass number } & ? & 16 & 37 & ? \\ \text { Atomic number } & ? & 8 & ? & ? \\ \text { Number of protons } & ? & ? & ? & ? \\ \text { Number of neutrons } & ? & ? & ? & 12 \\ \text { Number of electrons } & ? & ? & 17 & 11 \\ \hline \end{array} $$

Uranium exists mainly as two isotopes in nature, possessing mass numbers 235 and 238 . Write the full atomic symbols for both isotopes.

Consider the symbol \({ }_{7}^{14} \mathrm{C}\). (a) What is wrong with this symbol? (b) Adjust the atomic number so that the symbol is correct. (c) Adjust the symbol letter so that the symbol is correct.

Write the full atomic symbol for the only atom that has its mass number equal to its atomic number.

What is the difference between an atom's atomic mass and its mass number?

Why is the atomic mass scale also called the relative atomic mass scale?

What is so special about the mass number and atomic mass of \({ }_{6}^{12} \mathrm{C}\) ?

How much more massive is an "average" oxygen atom than \(\mathrm{a}_{6}^{12} \mathrm{C}\) atom? (Use the periodic table for the atomic mass of oxygen.)

How much more massive is an "average" titanium (Ti) atom than a \({ }_{6}^{12} \mathrm{C}\) atom? (Use the periodic table for the atomic mass of titanium.)

How much more massive is an "average" oxygen atom than a He atom? (Use the atomic masses from the periodic table.)

Why is the atomic mass of carbon not listed as 12 on the periodic table if the universal standard is that \({ }_{6}^{12} \mathrm{C}\) has an atomic mass of exactly 12 amu?

Suppose we wanted to use one of the more massive atoms, like \({ }_{92}^{235} \mathrm{U}\), as the standard reference for the atomic mass scale. (a) What would be the universally agreed-upon atomic mass of the \({ }^{235} \mathrm{U}\) isotope? (b) Why don't we use \({ }_{92}^{235} \mathrm{U}\) instead of \({ }_{6}^{12} \mathrm{C}\) ?

Bromine exists as only two isotopes in nature, \({ }_{35}^{79} \mathrm{Br}\) (atomic mass \(78.918336\) amu, \% natural abundance \(=50.69 \%\) and \({ }_{35}^{81}\) Br (atomic mass \(80.916289\) amu). (a) What is the percent natural abundance for \({ }_{35}^{81} \mathrm{Br}\) ? (b) Calculate the atomic mass of the naturally occurring mixture of isotopes.

Naturally occurring hydrogen on Earth has an atomic mass of \(1.0079\) amu. Suppose you were on another planet and found the atomic mass of hydrogen to be \(1.2000\) amu. How would you explain this? (The atomic mass of \({ }_{1}^{1} \mathrm{H}\) is \(1.0078252\) amu; the atomic mass of \({ }_{1}^{2} \mathrm{H}\) is \(2.1041022\) amu.)

While an atom's mass number and its atomic mass are not the same, they are often quite close to one another. Consider the following: Uranium- 235 has an atomic mass of \(235.04393\) amu and a percent abundance of \(0.73 \%\). Uranium-238 has an atomic mass of \(238.0508\) amu and a percent abundance of \(99.27 \%\). Without doing any calculations or consulting any other sources, which of the following do you think represents the atomic mass of naturally occurring uranium? (a) \(234.04 \mathrm{amu}\) (b) \(236.03 \mathrm{amu}\) (c) \(237.03\) amu (d) \(238.03\) amu (e) \(238.07\) amu Explain how you made your choice.

(a) In what unique way did Mendeleev order the elements to make his discovery? (b) What was his discovery? (c) How does his ordering differ from the modern ordering?

How did Mendeleev's discovery aid in discovering additional elements?

If one considers just the representative elements, how many groups would the periodic table have?