Chapter 4 Compounds and Their Bonds

Chapter 4 Compounds and Their Bonds
4.1 Octet Rule and Ions Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic and Covalent Bonds
Atoms that are not noble gases form octets to become more stable by losing, gaining, or sharing valence electrons by forming ionic bonds or covalent bonds Ionic bonds occur when atoms of one element lose valence electrons and the atoms of another element gain valence electrons. Covalent bonds occur when nonmetal atoms share electrons to attain a noble gas arrangement. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

The Octet Rule An octet is eight valence electrons
is associated with the stability of the noble gases (except He) The octet rule states that elements gain or lose electrons and become ions to attain noble gas arrangement. valence electrons He Ne 2, 8 8 Ar 2, 8, 8 8 Kr 2, 8, 14, 8 8 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic and Covalent Bonds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Metals Form Positive Ions
by a loss of their valence electrons with the electron configuration of the nearest noble gas that have fewer electrons than protons Group 1A metals ion 1+ Group 2A metals ion 2+ Group 3A metals ion 3+ Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of Magnesium Ion, Mg2+

Nonmetals Form Negative Ions
by a gain of valence electrons with the electron configuration of the nearest noble gas with fewer protons than electrons Group 5A nonmetals ion 3− Group 6A nonmetals ion 2− Group 7A nonmetals ion 1− Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of Chloride Ion, Cl−

Formulas and Names of Common Ions

Learning Check Write the formula and symbol of an ion with 16 protons and 18 electrons. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the formula and symbol of an ion with 16 protons and 18 electrons. The element with 16 protons is sulfur, with the symbol S. An ion of sulfur with 18 electrons gives sulfur a charge of 2−. The sulfide ion is S2−. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic Charges from Group Numbers
Group Charge Group 1A 1+ Group 2A 2+ Positive Charges Group 3A 3+ Group 5A 3− Group 6A 2− Negative Charges Group 7A 1− Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic Charges from Group Numbers

Learning Check Consider the elements calcium and chlorine. A. Identify each as a metal or a nonmetal. B. State the number of valence electrons for each. C. State the number of electrons that must be lost or gained for each to acquire an octet. D. Write the symbol, including its ionic charge, and name of each resulting ion. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Consider the elements calcium and chlorine. A. Identify each as a metal or a nonmetal. metal = calcium nonmetal = chlorine B. State the number of valence electrons for each. Calcium has two valence electrons. Chlorine has seven valence electrons. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution C. State the number of electrons that must be lost or gained for each to acquire an octet. Calcium will lose 2 electrons to acquire an octet. Chlorine will gain 1 electron to acquire an octet. D. Write the symbol, including its ionic charge, and name of each resulting ion. Ca2+ calcium Cl− chloride Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Properties of Ionic Compounds
consist of positive and negative ions have attractions called ionic bonds between positively and negatively charged ions have high melting points are solid at room temperature Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

NaCl Is an Ionic Compound

Formulas of Ionic Compounds
An ionic formula consists of positively and negatively charged ions is neutral has charge balance total positive charge = total negative charge The symbol of the metal is written first, followed by the symbol of the nonmetal. metal symbol, nonmetal symbol Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Subscripts in Formulas

Writing Ionic Formulas from Ion Charges
Subscripts in ionic compound represent the number of positive and negative ions that give an overall charge of zero. total positive charge + total negative charge = 0 therefore, total positive charge = total negative charge Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Charge Balance for Na2S In Na2S
2 Na atoms lose their valence electrons to become Na+ ions an S atom gains 2 electrons to become an S2− ion subscripts indicate number of each ions to give charge balance total positive charge = total negative charge Na+ Na+ + S2− = Na2S 2(1+) = 2− Write the symbol of the metal first followed by a subscript of 2 and then the symbol of the nonmetal. 2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing an Ionic Formula for Na3N
Charge balance is used to write the formula for sodium nitride, a compound containing Na+ and N3−. Na+ 3 Na N3− = Na3N 3(+1) (3−) = 0 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write the ionic formula of the compound formed with Ba2+ and Cl− ions. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the ionic formula of the compound formed with Ba2+ and Cl− ions. Write the symbols of the ions: Ba2+ Cl− Balance the charges: Ba Cl− Cl− = BaCl (1−) = 0 Write the ionic formula using a subscript 2 for two chloride ions. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Select the correct formula for each of the following ionic compounds. A. Na+ and O2− 1) NaO 2) Na2O 3) NaO2 B. Al3+ and Cl− 1) AlCl3 2) AlCl 3) Al3Cl C. Mg2+ and N3− 1) MgN 2) Mg2N3 3) Mg3N2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Select the correct formula for each of the following ionic compounds. A. Na+ and O2− 2) Na2O Check: 2Na+ + O2− = 2(1+) + 1(2−) = 0 B. Al3+ and Cl− 1) AlCl3 Check: Al3+ + 3Cl− = (3+) + 3(1−) = 0 C. Mg2+ and N3− 3) Mg3N2 Check: 3Mg2+ + 2N3− = 2(3+) + 2(3−) = 0 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Names of Some Ionic Compounds

Naming Ionic Compounds Containing Two Elements
Metals that form a single ion include the following: Metal(s) Ion Charge Group 1A 1+ Group 2A 2+ Al 3+ Zn and Cd 2+ Ag 1+ Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Naming Ionic Compounds

Naming the Ionic Compound K2O
Name the ionic compound K2O. Step 1 Identify the cation and anion. The cation, K+, is from Group 1A, and the anion, O2−, is from Group 6A. Step 2 Name the cation by its element name. The cation, K+, is potassium. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Naming the Ionic Compound K2O
Name the ionic compound K2O. Step 3 Name the anion by using the first syllable of its element name followed by ide. The anion, O2−, is oxide. Step 4 Write the name of the cation first and the name of the anion second. K2O is named potassium oxide. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write the names of the following compounds.
A. CaO ___________ B. Al2O3 ___________ C. MgCl2 ___________ Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the names of the following compounds.
Step 1 Identify the cation and anion. A. CaO: The cation, Ca2+, is from Group 2A, and the anion, O2−, is from Group 6A. B. Al2O3: The cation, Al3+, is from Group 3A, and the anion, O2−, is from Group 6A. C. MgCl2: The cation, Mg2+, is from Group 2A, and the anion, Cl−, is from Group 7A. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the names of the following compounds:
Step 2 Name the cation by its element name. A. CaO The cation, Ca2+, is calcium. B. Al2O3 The cation, Al3+, is aluminum. C. MgCl2 The cation, Mg2+, is magnesium. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the names of the following compounds.
Step 3 Name the anion by using the first syllable of its element name followed by ide. A. CaO The anion, O2−, is oxide. B. Al2O3 The anion, O2−, is oxide. C. MgCl2 The anion, Cl−, is chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the names of the following compounds:
Step 4 Write the name of the cation first and the name of the anion second. A. The name of CaO is calcium oxide. B. The name of Al2O3 is aluminum oxide. C. The name of MgCl2 is magnesium chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write the formulas and names for compounds of the following ions: Br− S2− N3− Na+ Al3+ Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the formulas and names for compounds of the following ions: Br− S2− N3− NaBr Na2S Na3N Na+ sodium bromide sodium sulfide sodium nitride AlBr Al2S AlN Al3+ aluminum aluminum aluminum bromide sulfide nitride Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Metals That Form More Than One Cation
Transition metals except for Zn2+, Cd2+, and Ag+ form two or more positive ions (cations). We use a Roman numeral to identify ionic charge. Cu2+ copper(II) Pb2+ lead(II) Cu+ copper(I) Pb4+ lead(IV) Fe2+ iron(II) Cr3+ chromium(III) Fe3+ iron(III) Cr6+ chromium(VI) Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Metals with Variable Charge

Determination of Variable Charge
Use the charge on the anion and charge balance to calculate charge on the metal ion. MnF2 Mn charge + 2 F− charge = 0 ? + 2 (1−) = 0 − = 0 Mn F− = 0 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Metals Form Positive Ions; Nonmetals Form Negative Ions

Naming Compounds with Variable Charge Metals

Naming FeCl2 Name the ionic compound FeCl2.
Step 1 Determine the charge of the cation. Because there are two Cl− anions, the charge on the Fe ion must be 2+. Step 2 Name the cation by its element name and use a Roman numeral in parenthesis for the charge. The charge on Fe is represented by a Roman numeral, iron(II). Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Naming FeCl2 Name the ionic compound FeCl2.
Step 3 Name the anion by using the first syllable of its element name followed by ide. Chlorine becomes chloride. Step 4 Write the name of the cation first and the name of the anion second. The ionic compound is named iron(II) chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Name the following ionic compounds containing metals that form two kinds of positive ions: A. Fe2O3 B. SnCl2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Name the following ionic compounds containing metals that form two kinds of positive ions: Step 1 Determine the charge of the cation. A. Fe2O3 Because there are three O2– anions and two Fe ions, the charge on the Fe ion must be 2+. B. SnCl2 Because there are two Cl− anions, the charge on the Sn ion must be 2+. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Name the following ionic compounds containing metals that form two kinds of positive ions: Step 2 Name the cation by its element name and use a Roman numeral in parenthesis for the charge. A. Fe2O3 The charge on Fe is represented by a Roman numeral: iron(III) B. SnCl2 The charge on Sn is represented by a Roman numeral: tin(II) Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Name the following ionic compounds containing metals that form two kinds of positive ions: Step 3 Name the anion by using the first syllable of its element name followed by ide. A. Fe2O3 Oxygen becomes oxide. B. SnCl2 Chlorine becomes chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Name the following ionic compounds containing metals that form two kinds of positive ions: Step 4 Write the name of the cation first and the name of the anion second. A. Fe2O3 is iron(III) oxide. B. SnCl2 is tin(II) chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing Formulas from the Name of an Ionic Compound

Formula for Chromium(III) Bromide
56 Step 1 Identify the cation and anion. The Roman numeral (III) indicates that the charge on the chromium ion is 3+, Cr3+. Step 2 Balance the charges. Cr3+ Br− Br− 1(3+) + 3(1−) = 0 Step 3 Write formula, cation first, using subscripts from the charge balance CrBr3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write chemical formulas for the following compounds:
A. Nickel(II) sulfide B. Zinc chloride C. Iron(III) oxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write chemical formulas for the following compounds.
Step 1 Identify the cation and anion. A. Nickel(II) sulfide The Roman numeral (II) indicates that the charge on the nickel ion is 2+, Ni2+. B. Zinc chloride Zinc is one of the transition metals with a fixed charge of 2+, Zn2+. C. Iron(III) oxide The Roman numeral (III) indicates that the charge on the iron ion is 3+, Fe3+. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 2 Balance the charges. A. Nickel(II) sulfide Ni2+ S2− 1(2+) + 1(2−) = 0 B. Zinc chloride Zn2+ Cl− Cl− 1(2+) + 2(1−) = 0 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 2 Balance the charges. C. Iron(III) oxide Fe O2− 2(3+) + 3(2−) = 0 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write chemical formulas for the following compounds:
Step 3 Write formula, cation first using subscripts from the charge balance. A. Nickel(II) sulfide NiS B. Zinc chloride ZnCl2 C. Iron(III) oxide Fe2O3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polyatomic Ions Polyatomic Ions
are a group of atoms with an overall charge often consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen and oxygen usually have a 1−, 2−, or 3− charge Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Names of Polyatomic Ions
1. Names of most common polyatomic ions end in ate. SO42− sulfate PO43− phosphate NO3− nitrate 2. When a related ion has one less oxygen, its name ends in ite. SO32− sulfite PO33− phosphite NO2− nitrite Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

3. Exceptions to these rules are: CN− cyanide OH− hydroxide NH4+ ammonium 4. Add an H+ and reduce negative charge. CO32− + H+ = HCO3− carbonate + H+ = bicarbonate or hydrogen carbonate SO42− + H+ = HSO4− sulfate + H+ = bisulfate or hydrogen sulfate Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

5. Halogens form 4 polyatomic ions with oxygen each have a 1 charge. ClO4− perchlorate ClO3− chlorate ClO2− chlorite ClO− hypochlorite Sodium chlorite is used in the processing and bleaching of pulp from wood fibers and recycled cardboard. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Compounds Containing Polyatomic Ions
When writing formulas for ionic compounds containing polyatomic ions, we use the same rules of charge balance as those for simple ionic compounds. Consider the formula for magnesium nitrate: Mg NO3− NO3− (2+) (1−) = 0 Mg NO3− = Mg(NO3)2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Select the correct formula for each.
A. aluminum nitrate 1) AlNO3 2) Al(NO)3 3) Am(NO3)3 B. copper(II) nitrate 1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3) C. iron(III) hydroxide 1) FeOH 2) Fe3OH 3) Fe(OH)3 D. tin(IV) hydroxide 1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH) Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Select the correct formula for each.
A. aluminum nitrate 3) Al(NO3)3 B. copper(II) nitrate ) Cu(NO3)2 C. iron(III) hydroxide ) Fe(OH)3 D. tin(IV) hydroxide ) Sn(OH)4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Guide to Naming Ionic Compounds with Polyatomic Ions

Naming Compounds with Polyatomic Ions
Name the following ionic compounds: Step 1 Step 2 Step Step 4 cation/anion Name Name Name cation anion compound A. Ca(NO3)2 Ca2+ NO3− calcium nitrate calcium nitrate B. FePO4 Fe3+ PO43− iron(III) phosphate iron(III) phosphate Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Name each of the following compounds containing polyatomic ions. A. MgSO3 B. MgSO4 C. Ca(ClO3)2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Name the following ionic compounds:
Step 1 Step 2 Step Step 4 cation/anion Name Name Name cation anion compound A. MgSO3 Mg2+ SO32− magnesium sulfite magnesium sulfite B. MgSO4 Mg2+ SO42− magnesium sulfate magnesium sulfate C. Ca(ClO3)2 Ca2+ ClO3− calcium chlorate calcium chlorate Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Name each of the following compounds: A. Fe2(SO4)3
B. Ba3(PO3)2 C. PbCO3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Name the following ionic compounds:
Step 1 Step 2 Step Step 4 cation/anion Name Name Name cation anion compound A. Fe2(SO4)3 Fe3+ SO42− iron(III) sulfate iron(III) sulfate B. Ba3(PO3)2 Ba2+ PO33− barium phosphite barium phosphite C. PbCO3 Pb2+ CO32− lead(II) carbonate lead(II) carbonate Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Covalent Bonds Covalent compounds form
when atoms share electrons to complete octets between nonmetal atoms from Groups 4A, 5A, 6A, and 7A Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of a Hydrogen Molecule
A hydrogen molecule, H2, forms as the atoms move closer and the nucleus of one atom attracts the electron of the other is stable with 2 electrons (helium) has a shared pair of electrons Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of a Hydrogen Molecule – H2
A covalent bond forms as H atoms move close together to share electrons. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of Octets in Molecules – F2
In a fluorine, F2,, molecule, each F atom shares one electron to attain an octet. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing Electron-Dot Formulas
To draw the electron-dot formula for methane, CH4, we start with the electron-dot symbols for carbon and hydrogen we need four hydrogen atoms to complete carbon’s octet Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Double and Triple Covalent Bonds
A double bond: occurs when atoms share two pairs of electrons forms when there are not enough electrons to complete octets A triple bond: occurs when atoms share three pairs of electrons Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Guide to Drawing Electron-Dot Formulas

Electron-Dot Formulas for Some Covalent Compounds – CO2
Step 1 Determine the arrangement of atoms. O C O Step 2 Determine the total number of valence electrons. C 2(O) = CO2 4e− + 2(6−) = 16e− Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Electron-Dot Formulas for Some Covalent Compounds – CO2
Step 3 Attach each bonded atom to the central atom with a pair of electrons. Step 4 Place the remaining electrons using single or multiple bonds to complete octets. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Triple Bond – N2 In a nitrogen molecule, N2,
each N atom shares three electrons to gain an octet the multiple bond formed is called a triple bond the name is the same as the element Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Names and Formulas of Covalent Compounds
When naming covalent compounds: the first nonmetal in the formula is named by its element name the second nonmetal is named by using the first syllable of its name followed by ide if a subscript is used in the formula a prefix is used in front of its name when vowels o and o or a and o appear together, the first vowel is omitted Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Guide to Naming Covalent Compounds

Prefixes Used in Naming Covalent Compounds

Naming Covalent Compounds – NCl3
Name the covalent compound NCl3. Step 1 Name the first nonmetal by its element name. The first nonmetal (N) is nitrogen. Step 2 Name the second element by using the first syllable of its name followed by ide. The second nonmetal (Cl) is chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Naming Covalent Compounds – NCl3
Step 3 Add prefixes to indicate number of atoms. Because there is one nitrogen atom, no prefix is needed. The subscript three for the Cl atoms is shown as the prefix tri. NCl3, nitrogen trichloride Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Some Common Covalent Compounds

Learning Check Select the correct name for each compound.
A. SiCl4 1) silicon chloride 2) tetrasilicon chloride 3) silicon tetrachloride B. P2O5 1) phosphorus oxide 2) phosphorus pentoxide 3) diphosphorus pentoxide C. Cl2O7 1) dichlorine heptoxide 2) dichlorine oxide 3) chlorine heptoxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Select the correct name for each compound.
A. SiCl4 3) silicon tetrachloride B. P2O5 3) diphosphorus pentoxide C. Cl2O7 1) dichlorine heptoxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write the name of each covalent compound. A. CO B. NO2
C. PF3 D. CCl4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the name of each covalent compound.
Step 1 Name the first nonmetal by its element name. A. CO The first nonmetal (C) is carbon. B. NO2 The first nonmetal (N) is nitrogen. C. PF3 The first nonmetal (P) is phosphorus. D. CCl4 The first nonmetal (C) is carbon. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 2 Name the second element by using the first syllable of its name followed by ide. A. CO The second nonmetal (O) is oxide. B. NO2 The second nonmetal (O) is oxide. C. PF3 The second nonmetal (F) is fluoride. D. CCl4 The second nonmetal (Cl) is chloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 3 Add prefixes to indicate number of atoms. A. CO Because there is one carbon atom, no prefix is needed. The subscript 1 for the O atom is shown using the prefix mono. CO is carbon monoxide. B. NO2 Because there is one nitrogen atom, no prefix is needed. The subscript 2 for the O atoms is shown using the prefix di. NO2 is nitrogen dioxide. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 3 Add prefixes to indicate number of atoms. C. PF3 Because there is one phosphorus atom, no prefix is needed. The subscript 3 for F atoms is shown using the prefix tri. PF3 is phosphorus trifluoride. D. CCl4 Because there is one carbon atom, no prefix is needed. The subscript 4 for the Cl atoms is shown using the prefix tetra. CCl4 is carbon tetrachloride. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing Formulas for Covalent Compounds

Writing Formulas for Covalent Compounds – Diboron Trioxide
Write the formula for the covalent compound diboron trioxide. Step 1 Write the symbols in order of the elements in the name. The first nonmetal is boron (B) and the second nonmetal is oxygen (O). B O Step 2 Write any prefixes as subscripts. The prefix di in diboron indicates there are two boron atoms and is shown as a subscript after B. The prefix tri in trioxide indicates there are three oxygen atoms and is shown as a subscript after O. B2O3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write the correct formula for each of the following:
A. phosphorus pentachloride B. dinitrogen trioxide C. sulfur hexafluoride Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Write the correct formula for each of the following:
Step 1 Write the symbols in order of the elements in the name. A. phosphorus pentachloride The first nonmetal is phosphorus, (P) and the second nonmetal is chlorine, (Cl). P Cl B. dinitrogen trioxide The first nonmetal is nitrogen, (N) and the second nonmetal is oxygen, (O). N O C. sulfur hexafluoride The first nonmetal is sulfur, (S) and the second nonmetal is fluorine, (F). S F Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 2 Write any prefixes as subscripts. A. phosphorus pentachloride: No prefix for phosphorus indicates there is 1 phosphorus atom. The prefix penta in pentachloride indicates there are 5 chlorine atoms, and is shown as a subscript after Cl. PCl5 B. dinitrogen trioxide: The prefix di in dinitrogen indicates there are 2 nitrogen atoms and is shown as a subscript after N. The prefix tri in trioxide indicates there are 3 oxygen atoms and is shown as a subscript after O. N2O3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Step 2 Write any prefixes as subscripts. C. sulfur hexafluoride: No prefix for sulfur indicates there is 1 sulfur atom. The prefix hexa in hexafluoride indicates there are 6 fluorine atoms and is shown as a subscript after F. SF6 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Summary to Naming Simple Compounds

Learning Check Identify each compound as ionic or covalent, and give its correct name. A. SO3 B. BaCl2 C. (NH4)3PO3 D. Cu2CO3 E. N2O4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Study Tip: Ionic or Covalent
A compound is ionic if the first element in the formula or the name is a metal or the polyatomic ion NH4+ K2O K is a metal; compound is ionic; potassium oxide covalent if the first element in the formula or the name is a nonmetal N2O N is a nonmetal; compound is covalent; dinitrogen oxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Identify each compound as ionic or covalent and give its correct name. A. SO3 covalent – sulfur trioxide B. BaCl2 ionic – barium chloride C. (NH4)3PO3 ionic – ammonium phosphite D. Cu2CO ionic – copper(I) carbonate E. N2O4 covalent – dinitrogen tetroxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Electronegativity The electronegativity value
of an element indicates the attraction of an atom for the shared electrons in a bond increases from left to right going across a period on the periodic table is high for the nonmetals, with fluorine as the highest is low for the metals Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Electronegativity and the Periodic Table

Comparing Ionic, Polar, and Nonpolar Covalent Bonds

Comparing Nonpolar and Polar Bonds
In the nonpolar covalent bond of H2, electrons are shared equally. In the polar covalent bond of HCl, electrons are shared unequally. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Nonpolar Covalent Bonds
A nonpolar covalent bond occurs between nonmetals is an equal or almost equal sharing of electrons has a very small electronegativity difference Examples: Electronegativity Atoms Difference Type of Bond N-N  3.0 = 0.0 Nonpolar covalent Cl-Br 3.0  2.8 = 0.2 Nonpolar covalent H-Si 2.1  1.8 = 0.3 Nonpolar covalent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polar Covalent Bonds A polar covalent bond
occurs between nonmetal atoms is an unequal sharing of electrons has a moderate electronegativity difference Examples: Electronegativity Atoms Difference Type of Bond O-Cl  3.0 = 0.5 Polar covalent Cl-C 3.0  2.5 = 0.5 Polar covalent O-S  2.5 = 1.0 Polar covalent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic Bonds An ionic bond occurs between metal and nonmetal ions
is a result of electron transfer has a large electronegativity difference (1.8 or more) Examples: Electronegativity Atoms Difference Type of Bond Cl-K – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs 2.5 – 0.7 = 1.8 Ionic Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following: A. K-N B. N-O C. Cl-Cl D. H-Cl Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following: Difference Type of bond A. K-N ionic (I) B. N-O polar covalent (P) C. Cl-Cl 0.0 nonpolar covalent (NP) D. H-Cl 0.9 polar covalent (P) Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

VSEPR Theory Valence Shell Electron-Pair Repulsion Theory (VSEPR)
describes the orientation of electron groups around the central atom states that electron groups are arranged as far apart as possible around the central atom states that specific shape of a molecule is determined by the number of atoms attached to the central atom Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Two Electron Groups
In a molecule of BeCl2 there are only two electron groups around the central atom, Be, which is an exception to octet rule repulsion is minimized by placing the two groups on opposite sides of the Be atom, giving this a linear arrangement with bond angles of 180° the shape with two electron groups around the central atom is linear Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Three Electron Groups
In a molecule of BF3 there are only three electron groups around the central atom, B, which is an exception to octet rule repulsion is minimized by placing the three groups as far apart as possible at bond angles of 120° the shape with three electron groups around the central atom is trigonal planar Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Three Electron Groups
In a molecule of SO2 there are three electron groups around the central atom S: a single-bonded O atom, a double-bonded O atom, and a lone pair of electrons repulsion is minimized by placing the three groups as far apart as possible since one group is a lone pair, the shape is determined by the two O atoms bonded to S, giving the molecule its bent shape Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Four Electron Groups
In a molecule of CH4 there are four electron groups attached to H atoms around the central atom, C repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109° the shape with four bonds on the central atom is called tetrahedral Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

In a molecule of NH3 there are three electron groups attached to H atoms and a lone pair around the central atom, N repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109° the shape with three bonds on the central atom is called trigonal pyrimidal Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

In a molecule of H2O there are two electron groups attached to H atoms and two lone pairs around the central atom, O repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109° the shape with two bonds on the central atom is called bent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Molecular Shapes for Molecules

Guide to Predicting Molecular Shape

Predict Molecular Shape of H2S
Predict the shape of H2S. Step 1 Draw the electron-dot formula. Step 2 Arrange electron groups around the central atom to minimize repulsion. To minimize repulsion, electron groups have a tetrahedral arrangement. Step 3 Use the atoms bonded to the central atom determine the molecular shape. With two bonds and two lone pairs, the shape is bent. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. A. PF3 B. H2S C. CCl4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. Step 1 Draw the electron-dot formula. A. PF3 B. H2S C. CCl4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution State the number of electron groups, and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. Step 2 Arrange electron groups around the central atom to minimize repulsion. A. PF3 To minimize repulsion electron groups have a tetrahedral arrangement. B. H2S To minimize repulsion electron groups have a tetrahedral arrangement. C. CCl4 To minimize repulsion electron groups have a tetrahedral arrangement. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. Step 3 Use the atoms bonded to the central atom to determine the molecular shape. A. PF3 With three bonds and one lone pair, the shape is trigonal planar. B. H2S With two bonds and two lone pairs, the shape is bent. C. CCl4 With four bonds the shape is tetrahedral. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Nonpolar Molecules Nonpolar molecules
such as H2, Cl2, and O2 are nonpolar because they contain nonpolar bonds with polar bonds such as CO2 can be nonpolar if the polar bonds cancel each other in a symmetrical arrangement dipoles cancel out, which makes the molecule nonpolar Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polar Molecules Polar molecules such as HCl are polar
because one end of the molecule is more negatively charged than the other when polar bonds in the molecule do not cancel each other because the electrons are shared unequally in the polar covalent bond Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polar Molecules In polar molecules
with three or more atoms, the shape of the molecule determines whether the dipoles cancel or not there are often lone pairs around the central atom such as H2O, the dipoles do not cancel, making the molecule positive at one end and negative at the other end such as H2O, there is a dipole on the central atom Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Identify each of the following molecules as polar or nonpolar. Explain. A. PBr3 B. HBr C. CF4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Identify each of the following molecules as polar or nonpolar. Explain. Number Number Bonds Lone Pairs Geometry A. PBr trigonal pyrimidal The dipoles do not cancel; the molecule is polar. B. HBr linear The bond has a dipole; the molecule is polar. C. CF tetrahedral The bonds have dipoles; the dipoles cancel and the molecule is nonpolar. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Dipole-Dipole Attractions and Hydrogen Bonds
In covalent compounds, polar molecules exert attractive forces called dipole-dipole attractions form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to very electronegative atoms of F, O, or N Hydrogen bonds are the strongest force between molecules and play a major role in the shape of DNA. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Dispersion Forces Dispersion forces are
weak attractions between nonpolar molecules caused by temporary dipoles that develop when molecules bump into each other weak, but make it possible for nonpolar molecules to form liquids and solids Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Comparison of Bonding and Attractive Forces

Melting Points and Attractive Forces
of compounds are related to the strength of attractive forces between molecules or compounds are lower due to weak forces such as dispersion forces are higher due to stronger attractive forces such as hydrogen bonding are highest in ionic compounds due to the strong attractive forces between ions in the compound Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Melting Points of Selected Substances

Learning Check Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or dispersion forces. A. NCl3 B. H2O C. Br-Br D. KCl E. NH3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or dispersion forces. A. NCl3 dipole-dipole forces B. H2O hydrogen bonds C. Br-Br dispersion forces D. KCl ionic bonds E. NH3 hydrogen bonds Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Chapter 4 Compounds and Their Bonds

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