Chapter 2

State in your own words the law of conservation of mass. State the law in its modern form.

State in your own words the law of constant composition.

Two basic laws of chemistry are the law of conservation of mass and the law of constant composition. Which of these laws (if any) do the following statements illustrate? (a) Lavoisier found that when mercury(II) oxide, \(\mathrm{HgO}\), decomposes, the total mass of mercury(Hg) and oxygen formed equals the mass of mercury(II) oxide decomposed. (b) Analysis of the calcium carbonate found in the marble mined in Carrara, Italy, and in the stalactites of the Carlsbad Caverns in New Mexico gives the same value for the percentage of calcium in calcium carbonate. (c) Hydrogen occurs as a mixture of two isotopes, one of which is twice as heavy as the other.

Who discovered the electron? Describe the experiment that led to the deduction that electrons are negatively charged particles.

Who discovered the nucleus? Describe the experiment that led to this discovery.

Selenium is widely sold as a dietary supplement. It is advertised to "protect" women from breast cancer. Write the nuclear symbol for naturally occurring selenium. It has 34 protons and 46 neutrons.

Radon is a radioactive gas that can cause lung cancer. It has been detected in the basements of some homes. How many protons are there in a Rn-220 atom? How many neutrons?

How do the isotopes of Cu-63 and Cu-65 differ from each other? Write nuclear symbols for both.

Consider two isotopes Fe-54 and Fe-56. (a) Write the nuclear symbol for both isotopes. (b) How do they differ from each other?

Uranium-235 is the isotope of uranium commonly used in nuclear power plants. How many (a) protons are in its nucleus? (b) neutrons are in its nucleus? (c) electrons are in a uranium atom?

Selenium-75 is used in the diagnosis of disorders related to the pan- creas. How many (a) protons are in its nucleus? (b) neutrons are in its nucleus? (c) electrons are in a selenium atom?

Nuclei with the same mass number but different atomic numbers are called isobars. Consider Ca-40, Ca-41, K-41 and Ar-41. (a) Which of these are isobars? Which are isotopes? (b) What do \(\mathrm{Ca}-40\) and \(\mathrm{Ca}-41\) have in common? (c) Correct the statement (if it is incorrect): Atoms of \(\mathrm{Ca}-41, \mathrm{~K}-41\), and Ar-41 have the same number of neutrons.

WEB See the definition of isobars in Question 15. Consider Na-21 and write the nuclear symbol for (a) an isotope of Na-21 that has one more neutron than \(\mathrm{Na}-21\). (b) an isobar of Na-21 with atomic number 10 . (c) a nucleus with 11 protons and 12 neutrons. Is this nucleus an isotope of \(\mathrm{Na}-21\) ?

Give the symbols for (a) potassium (b) cadmium (c) aluminum (d) antimony (e) phosphorus

Name the elements represented by the symbols (a) \(\mathrm{Mn}\) (b) \(\mathrm{Na}\) (c) As (d) \(S\) (e) \(\mathrm{Pb}\)

How many metals are in the following groups? (a) Group 1 (b) Group 13 (c) Group 17

How many nonmetals are in the following periods? (a) period 2 (b) period 4 (c) period 6

Which group in the periodic table (a) has one metalloid and no nonmetals? (b) has no nonmetals or transition metals? (c) has no metals or metalloids?

Which period of the periodic table (a) has no metals? (b) has no nonmetals? (c) has one post-transition metal and two metalloids?

Given the following condensed formulas, write the molecular formulas for the following molecules. (a) dimethylamine \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\) (b) propyl alcohol \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{OH}\) 26\. Write the condensed structural formulas and molecular formulas

\- Give the number of protons and electrons in (a) an \(\mathrm{N}_{2}\) molecule (identified in 1772 ). (b) an \(\mathrm{N}_{3}^{-}\) unit (synthesized in 1890 ). (c) an \(\mathrm{N}_{5}{\underline{\phantom{xx}}}^{+}\) unit (synthesized in 1999). (d) an \(\mathrm{N}_{5} \mathrm{~N}_{5}\) salt (a U.S. Air Force research team's synthesis project).

Give the number of protons and electrons in (a) a \(\mathrm{C}_{60}\) molecule. (b) a CN- ion. (c) a \(\mathrm{CO}_{2}\) molecule. (d) an \(\mathrm{N}^{3-}\) ion.

Complete the table below. If necessary, use the periodic table. $$ \begin{array}{ccccc} \begin{array}{c} \text { Nuclear } \\ \text { Symbol } \end{array} & \text { Charge } & \begin{array}{c} \text { Number of } \\ \text { Protons } \end{array} & \begin{array}{c} \text { Number of } \\ \text { Neutrons } \end{array} & \begin{array}{c} \text { Number of } \\ \text { Electrons } \end{array} \\ \hline 31 \mathrm{p} & 0 & 9 & 10 & \\ \hline & 0 & & 16 & \\ \hline & +3 & 27 & 30 & \\ \hline & & & 16 & 16 & 18 \\ \hline \end{array} $$

Classify the following compounds as electrolytes or non-electrolytes. (a) potassium chloride, KCl. (b) hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). (c) methane, \(\mathrm{CH}_{4}\) (d) barium nitrate, \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\).

Which (if any) of the following compounds are electrolytes? (a) glucose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) (b) ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\). (c) magnesium sulfide, \(\mathrm{MgS}\). (d) sulfur hexafluoride, \(\mathrm{SF}_{6}\).

Write the formulas for the following molecules. (a) methane (b) carbon tetraiodide (c) hydrogen peroxide (d) nitrogen oxide (e) silicon dioxide

Write the formulas for the following molecules. (a) water (b) ammonia (c) hydrazine (d) sulfur hexafluoride (e) phosphorus pentachloride

Write the names of the following molecules. (a) \(\mathrm{ICl}_{3}\) (b) \(\mathrm{N}_{2} \mathrm{O}_{5}\) (c) \(\mathrm{PH}_{3}\) (d) \(\mathrm{CBr}_{4}\) (e) \(\mathrm{SO}_{3}\)

Write the names of the following molecules. (a) \(\mathrm{CO}\) (b) \(\mathrm{SiC}\) (c) \(\mathrm{XeF}_{6}\) (d) \(\mathrm{P}_{4} \mathrm{O}_{10}\) (e) \(\mathrm{C}_{2} \mathrm{H}_{2}\)

Give the formulas of all the compounds containing no ions other than \(\mathrm{K}^{+}, \mathrm{Ca}^{2+}, \mathrm{Cl}^{-}\), and \(\mathrm{S}^{2-} .\)

Give the formulas of compounds in which (a) the cation is \(\mathrm{Ba}^{2+}\), the anion is \(\mathrm{I}^{-}\) or \(\mathrm{N}^{3-}\). (b) the anion is \(\mathrm{O}^{2-}\), the cation is \(\mathrm{Fe}^{2+}\) or \(\mathrm{Fe}^{3+}\)

Write the formulas of the following ionic compounds. (a) iron(III) carbonate (b) sodium azide \(\left(\mathrm{N}_{3}-\right)\) (c) calcium sulfate (d) copper(I) sulfide (e) lead(IV) oxide

Write formulas for the following ionic compounds. (a) cobalt(II) acetate (b) barium oxide (c) aluminum sulfide (d) potassium permanganate (e) sodium hydrogen carbonate

Write the names of the following ionic compounds. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) (c) \(\mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\) (d) AlN (e) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\)

Write the names of the following ionic compounds. (a) \(\mathrm{ScCl}_{3}\) (b) \(\mathrm{Sr}(\mathrm{OH})_{2}\) (c) \(\mathrm{KMnO}_{4}\) (d) \(\mathrm{Rb}_{2} \mathrm{~S}\) (e) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\)

Write the names of the following ionic compounds. (a) \(\mathrm{HCl}(a q)\) (b) \(\mathrm{HClO}_{3}(a q)\) (c) \(\mathrm{Fe}_{2}\left(\mathrm{SO}_{3}\right)_{3}\) (d) \(\mathrm{Ba}\left(\mathrm{NO}_{2}\right)_{2}\) (e) \(\mathrm{NaClO}\)

Write formulas for the following ionic compounds. (a) hydrochloric acid (b) sodium nitrite (c) chromium(III) sulfite (d) potassium chlorate (e) iron(III) perbromate

Write the formulas and names of the following: (a) An ionic compound whose cation is a transition metal with 25 protons and 22 electrons and whose anion is an oxoanion of nitro- gen with two oxygen atoms. (b) A molecule made up of a metalloid in Group 13 and three atoms of a halogen in period 2 . (c) An ionic compound made up of an alkaline earth with 20 protons, and an anion with one hydrogen atom, a carbon atom, and 3 oxygen atoms.

Identify the following elements: (a) A member of the same period as tellurium with two fewer protons than tellurium. (b) A transition metal in Group 5, period 4. (c) An alkali with 55 protons. (d) A metalloid in Group 15 with more than 40 protons.

Hydrogen- 1 can take the form of a molecule, an anion \(\left(\mathrm{H}^{-}\right)\), or a cation \(\left(\mathrm{H}^{+}\right)\). (a) How many protons, electrons, and neutrons are in each possible species? (b) Write the name and formula for the compound formed between hydrogen and a metal in Group 2 with 12 protons. (c) What is the general name of the aqueous compounds in which hydrogen is a cation?

A molecule of ethylamine is made up of two carbon atoms, seven hydrogen atoms, and one nitrogen atom. (a) Write its molecular formula. (b) The reactive group in ethylamine is \(\mathrm{NH}_{2}\). Write its condensed structural formula.

Criticize each of the following statements. (a) In an ionic compound, the number of cations is always the same as the number of anions. (b) The molecular formula for strontium bromide is \(\mathrm{SrBr}_{2}\). (c) The mass number is always equal to the atomic number. (d) For any ion, the number of electrons is always more than the number of protons.

Which of the following statements is/are always true? Never true? Usually true? (a) Compounds containing carbon atoms are molecular. (b) A molecule is made up of nonmetal atoms. (c) An ionic compound has at least one metal atom.

Which statements are true? (a) Neutrons have neither mass nor charge. (b) Isotopes of an element have an identical number of protons. (c) C-14 and N-14 have identical neutron/proton (n/p \(^{+}\) ) ratios. (d) The vertical columns in a periodic table are referred to as "groups." (e) When an atom loses an electron, it becomes positively charged.

A student saw the following nuclear symbol for an unknown element: \({ }_{11}^{33} \mathrm{X} .\) Which of the following statements about \(\mathrm{X}\) and \({ }_{11}^{23} \mathrm{X}\) are true? (a) \(\mathrm{X}\) is sodium. (b) \(\mathrm{X}\) is vanadium. (c) \(\mathrm{X}\) has 23 neutrons in its nucleus. (d) \(\mathrm{X}^{2+}\) has 13 electrons. (e) \({ }_{11}^{23} \mathrm{X}\) has a proton/neutron ratio of about \(1.1\).

Write the atomic symbol for the element whose ion has a - 2 charge, has 20 more neutrons than electrons, and has a mass number of 126 .

Mercury(II) oxide, a red powder, can be decomposed by heating to produce liquid mercury and oxygen gas. When a sample of this compound is decomposed, \(3.87 \mathrm{~g}\) of oxygen and \(48.43 \mathrm{~g}\) of mercury are produced. \(\operatorname{In}\) a second experiment, \(15.68 \mathrm{~g}\) of mercury is allowed to react with an excess of oxygen and \(16.93 \mathrm{~g}\) of red mercury(II) oxide is produced. Show that these results are consistent with the law of constant composition.

Consider the elements oxygen, fluorine, argon, sulfur, potassium, and strontium. From this group of elements, which ones fit the descriptions below? (a) Two elements that are metals. (b) Four elements that are nonmetals. (c) Three elements that are solid at room temperature. (d) An element that is found in nature as \(\mathrm{X}_{8}\). (e) One pair of elements that may form a molecular compound. (f) One pair of elements that may form an ionic compound with formula \(\mathrm{AX}\) (g) One pair of elements that may form an ionic compound with formula \(\mathrm{AX}_{2}\) (h) One pair of elements that may form an ionic compound with formula \(\mathrm{A}_{2} \mathrm{X} .\) (i) An element that can form no compounds. (j) Three elements that are gases at room temperature.

Three compounds containing only carbon and hydrogen are analyzed. The results for the analysis of the first two compounds are given below: $$ \begin{array}{ccc} \hline \text { Compound } & \text { Mass of Carbon (g) } & \text { Mass of Hydrogen (g) } \\ \hline \text { A } & 28.5 & 2.39 \\ \text { B } & 34.7 & 11.6 \\ \text { C } & 16.2 & \- \\ \hline \end{array} $$ Which, if any, of the following results for the mass of hydrogen in compound C follows the law of multiple proportions? (a) \(5.84 \mathrm{~g}\) (b) \(3.47 \mathrm{~g}\) (c) \(2.72 \mathrm{~g}\)

Ethane and ethylene are two gases containing only hydrogen and carbon atoms. In a certain sample of ethane, \(4.53 \mathrm{~g}\) of hydrogen is combined with \(18.0 \mathrm{~g}\) of carbon. In a sample of ethylene, \(7.25 \mathrm{~g}\) of hydrogen is combined with \(43.20 \mathrm{~g}\) of carbon. (a) Show how the data illustrate the law of multiple proportions. (b) Suggest reasonable formulas for the two compounds.