Chapter 4 Compounds and Their Bonds 4.1 Octet Rule and Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Octet Rule An octet is 8 valence electrons. is associated with the stability of the noble gases. He is stable with 2 valence electrons (duet). valence electrons He 2 2 Ne 2, 8 8 Ar 2, 8, 8 8 Kr 2, 8, 14, 8 8

Ionic and Covalent Bonds Atoms form octets to become more stable. by losing, gaining, or sharing valence electrons. by forming ionic bonds or covalent bonds. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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+ Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Formation of a Sodium Ion, Na+ Sodium achieves an octet by losing its one valence electron. 2, 8, 1 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge of Sodium Ion, Na+ With the loss of its valence electron, the sodium ion has a +1 charge. Sodium atom Sodium ion 11p+ 11p+ 11e- 10e- 0 1+ 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Formation of Mg2+ Magnesium achieves an octet by losing its two valence electrons. 2, 8, 2 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge of Magnesium Ion Mg2+ With the loss of two valence Electrons, magnesium forms a positive ion with a +2 charge. Mg atom Mg2+ ion 12p+ 12p+ 12e- 10e- 0 2+ Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check A. The number of valence electrons in aluminum is 1) 1e-. 2) 2e-. 3) 3e-. B. The change in electrons for octet requires a 1) loss of 3e-. 2) gain of 3e-. 3) a gain of 5e-. C. The ionic charge of aluminum is 1) 3-. 2) 5-. 3) 3+. D. The symbol for the aluminum ion is 1) Al3+. 2) Al3-. 3) Al+.

Formation of Negative Ions In ionic compounds, nonmetals achieve an octet arrangement. gain electrons. form negatively charged ions with 3-, 2-, or 1- charges.

Formation of a Chloride, Cl- Chlorine achieves an octet by adding an electron to its valence electrons. 2, 8, 7 2, 8, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge of a Chloride Ion, Cl- By gaining one electron, the chloride ion has a -1 charge. Chlorine atom Chloride ion 17p+ 17p+ 17e- 18e- 0 1– Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionic Charge from Group Numbers The charge of a positive ion is equal to its Group number. Group 1A(1) = 1+ Group 2A(2) = 2+ Group 3A(3) = 3+ The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group 6A(16) = 6 - 8 = 2- or 16 - 18 = 2-

Some Ionic Charges I- Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check A. The number of valence electrons in sulfur is 1) 4e-. 2) 6e-. 3) 8e-. B. The change in electrons for octet requires a 1) loss of 2e-. 2) gain of 2e-. 3) a gain of 4e-. C. The ionic charge of sulfur is 1) 2+. 2) 2-. 3) 4-.

Chapter 4 Compounds and Their Bonds 4.2 Ionic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionic Compounds Ionic compounds consist of positive and negative ions. have attractions called ionic bonds between positively and negatively charged ions. have high melting and boiling points. are solid at room temperature.

Salt is An Ionic Compound Sodium chloride or “table salt” is an example of an ionic compound. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionic Formulas 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.

Charge Balance for NaCl, “Salt” In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. the symbol of the metal is written first followed by the symbol of the nonmetal. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge Balance In MgCl2 In MgCl2, a Mg atom loses two valence electrons. two Cl atoms each gain one electron. subscripts indicate the number of ions needed to give charge balance. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge Balance in Na2S In Na2S. two Na atoms lose one valence electron each. one S atom gains two electrons. subscripts show the number of ions needed to give charge balance. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Writing Ionic Formulas from Charges Charge balance is used to write the formula for sodium nitride, a compound containing Na+ and N3−. Na+ 3 Na+ + N3− = Na3N 3(+1) + 1(3-) = 0

Formula from Ionic Charges Write the ionic formula of the compound with Ba2+ and Cl. Write the symbols of the ions. Ba2+ Cl Balance the charges. Ba2+ Cl two Cl- needed Cl Write the ionic formula using a subscript 2 for two chloride ions that give charge balance. BaCl2

Learning Check Select the correct formula for each of the following ionic compounds. A. Na+ and S2- 1) NaS 2) Na2S 3) NaS2 B. Al3+ and Cl- 1) AlCl3 2) AlCl 3) Al3Cl C. Mg2+ and N3- 1) MgN 2) Mg2N3 3) Mg3N2

Chapter 4 Compounds and Their Bonds 4.3 Naming and Writing Ionic Formulas Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Ionic Compounds with Two Elements To name a compound that contains two elements, identify the cation and anion. name the cation first followed by the name of the anion.

Charges of Representative Elements Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Names of Some Common Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Complete the names of the following ions. Ba2+ Al3+ K+ _________ __________ _________ N3 O2 F _________ __________ _________ P3 S2 Cl

Examples of Ionic Compounds with Two Elements Formula Ions Name cation anion NaCl Na+ Cl- sodium chloride K2S K+ S2- potassium sulfide MgO Mg2+ O2- magnesium oxide CaI2 Ca2+ I- calcium iodide Al2O3 Al3+ O2- aluminum oxide

Learning Check Write the names of the following compounds. 1) CaO ___________ 2) KBr ___________ 3) Al2O3 ___________ 4) MgCl2 ___________

Learning Check Write the formulas and names for compounds of the following ions: Br− S2− N3− Na+ Al3+

Transition Metals form Positive Ions Most transition metals and Group 4(14) metals form 2 or more positive ions. Zn2+, Ag+, and Cd2+ form only one ion.

Metals that form more than One Cation The name of metals with two or more positive ions (cations) use a Roman numeral to identify ionic charge. Lead Pb2+ lead(II) Pb4+ lead(IV) Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Ionic Compounds with Variable Charge Metals Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Variable Charge Metals Transition metals with two different ions use a Roman numeral after the name of the metal to indicate ionic charge.

Naming FeCl2 To name FeCl2 1. Determine the charge of the cation using the charge of the anion (Cl-). Fe ion + 2 Cl- = Fe ion + 2- = 0 Fe ion = 2+ 2. Name the cation by the element name and add a Roman numeral in parenthesis to show its charge. Fe2+ = iron(II) 3. Write the anion with an ide ending. FeCl2 = iron(II) chloride

Naming Cr2O3 To name Cr2O3 1. Determine the charge of cation from the anion (O2-). 2 Cr ions + 3 O2- = 0 2 Cr ions + 3(2-) = 0 2 Cr ions - 6 = 0 2 Cr ions = +6 Cr ion = 3+ = Cr3+ 2. Name the cation by the element name and add a Roman numeral in parenthesis to show its charge. Cr3+ = chromium(III) 3. Write the anion with an ide ending. chromium(III) oxide = Cr2O3

Learning Check Select the correct name for each. A. Fe2S3 1) iron sulfide 2) iron(II) sulfide 3) iron(III) sulfide B. CuO 1) copper oxide 2) copper(I) oxide 3) copper(II) oxide

Guide to Writing Formulas from the Name Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Writing Formulas Write a formula for potassium sulfide. 1. Identify the cation and anion. potassium = K+ sulfide = S2− 2. Balance the charges. K+ S2− K+ 2(1+) + 2(1-) = 0 3. 2 K+ and 1 S2− = K2S

Writing Formulas Write a formula for iron(III) chloride. 1. Identify the cation and anion. iron (III) = Fe3+ (III = charge of 3+) chloride = Cl− 2. Balance the charges. Fe3+ Cl− Cl− = (3+) + 3(1-) = 0 Cl− 3. 1 Fe3+ and 3 Cl− = FeCl3

Learning Check What is the correct formula for each of the following? A. Copper(I) nitride 1) CuN 2) CuN3 3) Cu3N B. Lead(IV) oxide 1) PbO2 2) PbO 3) Pb2O4

Solution The correct formula is A. Copper (I) nitride 3) Cu3N Need 3Cu+ and N3- B. Lead (IV) oxide 1) PbO2 Need Pb4+ and 2O2-

Chapter 4 Compounds and Their Bonds 4.4 Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Polyatomic Ions A polyatomic ion is a group of atoms. has an overall ionic charge. Some examples of polyatomic ions are NH4+ ammonium OH− hydroxide NO3− nitrate NO2− nitrite CO32− carbonate PO43− phosphate HCO3− hydrogen carbonate (bicarbonate)

Some Compounds with Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Some Names of Polyatomic Ions The names of common polyatomic anions end in ate. NO3− nitrate PO43− phosphate with one oxygen less end in ite. NO2− nitrite PO33− phosphite with hydrogen attached use the prefix hydrogen (or bi). HCO3− hydrogen carbonate (bicarbonate) HSO3− hydrogen sulfite (bisulfite)

Names and Formulas of Common Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Names and Formulas of Common Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Compounds with Polyatomic Ions The positive ion is named first followed by the name of the polyatomic ion. NaNO3 sodium nitrate K2SO4 potassium sulfate Fe(HCO3)3 iron(III) bicarbonate or iron(III) hydrogen carbonate (NH4)3PO3 ammonium phosphite

Some Compounds with Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Match each formula with the correct name. A. MgS 1) magnesium sulfite MgSO3 2) magnesium sulfate MgSO4 3) magnesium sulfide B. Ca(ClO3)2 1) calcium chlorate CaCl2 2) calcium chlorite Ca(ClO2)2 3) calcium chloride

Learning Check Name each of the following compounds: A. Mg(NO3)2 B. Cu(ClO3)2 C. PbO2 D. Fe2(SO4)3 E. Ba3(PO3)2

Writing Formulas with Polyatomic Ions The formula of an ionic compound containing a polyatomic ion must have a charge balance that equals zero (0). Na+ and NO3−  NaNO3 with two or more polyatomic ions has the polyatomic ions in parentheses. Mg2+ and 2NO3−  Mg(NO3)2 subscript 2 for charge balance

Learning Check Select the correct formula for each. A. aluminum nitrate 1) AlNO3 2) Al(NO)3 3) Al(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)

Learning Check Write the correct formula for each. A. potassium bromate B. calcium carbonate C. sodium phosphate D. iron(III) oxide E. iron(II) nitrite

Rules for Naming Ionic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Flowchart for Naming Ionic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Name the following compounds: A. Ca3(PO4)2 B. FeBr3 C. Al2S3 D. Zn(NO2)2 E. NaHCO3

Learning Check Write the formulas for the following: A. calcium nitrate B. iron(II) hydroxide C. aluminum carbonate D. copper(II) bromide E. lithium phosphate

Chapter 4 Compounds and Their Bonds 4.5 Covalent Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Covalent Bonds Covalent bonds form when atoms share electrons to complete octets. between two nonmetal atoms. between nonmetal atoms from Groups 4A(14), 5A(15), 6A(16), and 7A(17).

Hydrogen Molecule A hydrogen molecule is stable with two electrons (helium). has a shared pair of electrons.

Forming Octets in Molecules In a fluorine, F2,, molecule, each F atom shares one electron. attains an octet.

Carbon forms 4 covalent bonds In a CH4, methane, molecule a C atom shares 4 electrons to attain an octet. each H shares 1 electron to become stable like helium.

Multiple Bonds In nitrogen molecule, N2, each N atom shares 3 electrons. each N attains an octet. the bond is a multiple bond called a triple bond. the name is the same as the element.

Naming Covalent Compounds To name covalent compounds STEP 1: Name the first nonmetal as an element. STEP 2: Name the second nonmetal with an ide ending. STEP 3: Use prefixes to indicate the number of atoms (subscript) of each element. Table4.12

Naming Covalent Compounds What is the name of SO3? 1. The first nonmetal is S sulfur. 2. The second nonmetal is O named oxide. 3. The subscript 3 of O is shown as the prefix tri. SO3  sulfur trioxide The subscript 1 (for S) or mono is understood.

Naming Covalent Compounds Name P4S3. 1. The first nonmetal P is phosphorus. 2. The second nonmetal S is sulfide. 3. The subscript 4 of P is shown as tetra. The subscript 3 of O is shown as tri. P4S3  tetraphosphorus trisulfide

Formulas and Names of Some Covalent Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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

Learning Check Write the name of each covalent compound. PCl3 _____________________ CCl4 _____________________ N2O _____________________

Guide to Writing Formulas The prefixes in the name are used to write the formula. STEP 1: Write the symbols in the order of the elements in the name. STEP 2: Write any prefixes as subscripts. Example: Write the formula for carbon disulfide. STEP 1: Elements are C and S STEP 2: No prefix for carbon means 1 C Prefix di = 2 Formula: CS2

Learning Check Write the correct formula for each of the following. A. phosphorus pentachloride B. dinitrogen trioxide C. sulfur hexafluoride

Learning Check Identify each compound as ionic or covalent and give its correct name. A. SO3 B. BaCl2 C. (NH4)3PO4 D. Cu2CO3 E. N2O4

Learning Check Name the following compounds. A. Ca3(PO4)2 B. FeBr3 C. SCl2 D. Cl2O E. N2

Learning Check Write the formulas for the following. A. calcium nitrate B. boron trifluoride C. aluminum carbonate D. dinitrogen tetroxide E. copper(I) phosphate

Chapter 4 Compounds and Their Bonds 4.6 Electronegativity and Bond Polarity Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Electronegativity The electronegativity value indicates the attraction of an atom for shared electrons. 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.

Some Electronegativity Values for Group A Elements Electronegativity decreases ` Electronegativity increases High values ` Low values Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetals. is an equal or almost equal sharing of electrons. has almost no electronegativity difference (0.0 to 0.4). Examples: Electronegativity Atoms Difference Type of Bond N-N 3.0 - 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

Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms. is an unequal sharing of electrons. has a moderate electronegativity difference (0.5 to 1.7). Examples: Electronegativity Atoms Difference Type of Bond O-Cl 3.5 - 3.0 = 0.5 Polar covalent Cl-C 3.0 - 2.5 = 0.5 Polar covalent O-S 3.5 - 2.5 = 1.0 Polar covalent

Comparing Nonpolar and Polar Covalent Bonds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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 3.0 – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs 2.5 – 0.7 = 1.8 Ionic

Electronegativity and Bond Types TABLE 4.14

Predicting Bond Types Table 4.15

Learning Check Use the electronegativity difference to identify the type of bond between the following: nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K-N B. N-O C. Cl-Cl D. H-Cl

Chapter 4 Compounds and Their Bonds 4.7 Shapes and Polarity of Molecules Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

VSEPR In the valence-shell electron-pair repulsion theory (VSEPR), the electron groups around a central atom are arranged as far apart from each other as possible. have the least amount of repulsion of the negatively charged electrons. have a geometry around the central atom that determines molecular shape.

Guide to Predicting Molecular Shape (VSEPR Theory) 1. Write the electron-dot structure. 2. Arrange the electron groups around the central atom to minimize repulsion. 3. Use the atoms bonded to the central to determine the shape of the molecule.

Four Electron Groups In a molecule of CH4, there are four electron groups around C. repulsion is minimized by placing four electron groups at angles of 109°, which is a tetrahedral arrangement. the shape with four bonded atoms is tetrahedral. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Three Bonding Atoms and One Lone Pair In a molecule of NH3, three electron groups bond to H atoms and the fourth one is a lone (nonbonding) pair. repulsion is minimized with 4 electron groups in a tetrahedral arrangement. with three bonded atoms, the shape is pyramidal. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Two Bonding Atoms and Two Lone Pairs In a molecule of H2O, two electrons groups are bonded to H atoms and two are lone pairs (4 electron groups). four electron groups minimize repulsion in a tetrahedral arrangement. the shape with two bonded atoms is bent(~109). Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Shapes with 4 Electron Groups Bonded Atoms Lone Pairs Bond Angles Molecular Shape Example 4 109 tetrahedral CH4 3 1 ~109 Pyramidal NH3 2 Bent H2O Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check State the number of electron groups, lone pairs, and use VSEPR theory to determine the shape of the following molecules or ions. 1) tetrahedral 2) pyramidal 3) bent A. PF3 B. H2S C. CCl4

Polar Molecules A polar molecule contains polar bonds. has a separation of positive and negative charge called a dipole indicated with + and -. has dipoles that do not cancel. + - • • H–Cl H—N—H dipole H dipoles do not cancel

Nonpolar Molecules A nonpolar molecule contains nonpolar bonds. Cl–Cl H–H or has a symmetrical arrangement of polar bonds. O=C=O Cl Cl–C–Cl Cl dipoles cancel

Determining Molecular Polarity STEP 1: Write the electron-dot formula. STEP 2: Determine the polarity of the bonds. STEP 3: Determine if dipoles cancel. Example: H2O . . H─O: H2O is polar │ H dipoles do not cancel

Learning Check Identify each of the following molecules as 1) polar or 2) nonpolar. Explain. A. PBr3 B. HBr C. Br2 D. SiBr4