Chapter 6 Compound & Bonds PDF

Chapter 6 Compound & Bonds Learning Goals: 1. Definition of octet rule 2. Using octet rule to write symbols for simple ions of representative elements 3. Using charge balance to write formula for ionic compound 4. Define ionic and covalent bonds 5. Name compound when given the formula 6. Gi...

Chapter 6 Compound & Bonds Learning Goals: 1. Definition of octet rule 2. Using octet rule to write symbols for simple ions of representative elements 3. Using charge balance to write formula for ionic compound 4. Define ionic and covalent bonds 5. Name compound when given the formula 6. Give formula when given the name 1 Chapter 6 Compounds and Their Bonds Octet Rule and Ions General, Organic, and Biological Chemistry 2  Ionic and Covalent Bonds Chemical bonds are formed when atoms lose, gain, or share valence electrons to acquire an octet of eight valence electrons (octet rule). Ionic bonds occur when valence electrons of a metal atom are transferred to the atom of a nonmetal. Covalent bonds occur when nonmetal atoms share electrons to attain a noble gas arrangement.  The Octet Rule Is the tendency of atoms to attain noble gas electron configuration - To have 8 valence electrons - is associated with the stability of the noble gasses - does not occur with He; He is stable with 2 valence electrons (duet) Valence Electrons (from previous chapter) He 2 Ne 8 Ar 8 Kr 8 4  Ions Ions are atoms that has a charge Atoms form positively charged ions when they lose electrons and negatively charged ions when they gain electrons. For a Neutral atom  Number of p+ = Number of e- (review from previous chapter) For an Anion  Ions with negative charge Number of p+ < Number of e- For a Cation  Ions with positive charge Number of p+ > Number of e-  Ionic and Covalent Bonds Atoms form octets  to become more stable  by losing, gaining, or sharing valence electrons  by forming ionic or covalent bonds General, Organic, and Biological Chemistry 6  Metals Form Positive Ions Metals form positive ions (p+ > e-)  by loss of their valence electrons  with the electron configuration of the nearest noble gas ( 8 valence e-)  that have fewer electrons than protons Group 1A(1) metals  ion 1+ (1 more p+ than e-) Group 2A(2) metals  ion 2+ (2 more p+ than e-) Group 3A(3) metals  ion 3+ (3 more p+ than e-) (look closely at the group number compared to ion charge) 7 Example: Formation of a Sodium Ion, Na+ Sodium achieves an octet by losing its one valence electron. Again Look at Group number and charge of the ion that will form 8 Charge of Sodium Ion, Na+ With the loss of its valence electron, a sodium ion has a 1+ charge. (1 more p+ than e-) Sodium atom Sodium ion 11p+ 11p+ 11e– 10e– 0 1+ Na atom p+ = e- Na ion p+ > e- General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9 EXAMPLE: Formation of Magnesium Ion, Mg2+ Magnesium achieves an octet by losing its two valence electrons. Again Look at Group number and charge of the ion that will form 10  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+ Mg atom p+ = e- Mg ion p+ > e- General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11 Formation of Negative Ions In ionic compounds, nonmetals  achieve an octet arrangement  gain electrons  form negatively charged ions with 3–, 2–, or 1– charges General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 12 EXAMPLE: Formation of a Chloride Ion, Cl– Chlorine achieves an octet by adding/gaining an electron to its valence electrons. Again Look at Group number and charge of the ion that will form; 13 For non-metals the charge is (group number minus 18)  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– Cl atom p+ = e- Cl ion p+ < e- Again Look at Group number and charge of the ion that will form; For non-metals the charge is (group number minus 18) Cl in group 17 so ion charge is 17-18 = -1 REVIEW: How to get Ionic Charge from Group Numbers  The charge of a positive ion (usually a metal) is equal to its Group number. Group 1A(1) = 1+ Group 2A(2) = 2+ Group 3A(3) = 3+  The charge of a negative ion (usually a non-metal) is obtained by subtracting 8 or 18 from its Group number. Group 6A(16) = 6–8 = 2– or 16 – 18 = 2– 15 Some Typical Ionic Charges Note how the anion changes name from the elemental name to ion name 16 (ending in -ide) Group Number and Ionic Charge Ions achieve the electron configuration of their nearest noble gas Ions of metals in Groups 1A(1), 2A(2), or 3A(13) have positive 1+, 2+, or 3+ charge. Ions of nonmetals in Groups 5A(15), 6A(16), or 7A(17) have negative 3–, 2–, or 1– charge. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 17 Groups Numbers for Some Positive and Negative Ions 18 Chemistry Link to Health: Important Ions in the Body Ions are important in regulating body functions. Ion Occurrence Function Source Na+ Principal cation Regulation and control of Salt, cheese, outside the cell body fluids pickles K+ Principal cation Regulation of body fluids Bananas, potatoes, outside the cell and cellular functions orange juice, milk Ca2+ Cation outside the Major cation in bones, Milk, yogurt, cell; found in bones needed for muscle cheese, greens, contractions spinach Mg2+ Cation outside the Essential for certain Chlorophyll, nuts, cell; found in bones enzymes, muscles, and grains nerve control  Study Check Write the formula and symbol of an ion with 16 protons and 18 electrons.  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− 0r 2 more e − than p + The sulfide ion is S2−. Again note how anion name changes from sulphur to sulphide (ending in –ide)  Study 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.  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 2 valence electrons. Chlorine has 7 valence electrons. (Review group number vs valence electrons from previous chapter Ca in group 2 chlorine in main group 7A)  Solution Consider the elements calcium and chlorine. C. State the number of electrons that must be lost or gained for each to acquire an octet. Calcium will lose two electrons to acquire an octet. Chlorine will gain one electron to acquire an octet. D. Write the symbol, including its ionic charge, and name of each resulting ion. Ca2+ calcium Cl− chloride Ca is metal Cl non-metal (loose e-, group 2 charge 2+) (gain e-, group 17 charge:17-18= 1-) Chapter 6 Compounds and Their Bonds Ionic Compounds General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 25 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 solids at room temperature General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 26  Salt Is an Ionic Compound Sodium chloride, or “table salt,” is an example of an ionic compound. The magnification of NaCl crystals shows the arrangement of Na+ and Cl− ions in an NaCl crystal. 27 Ionic Formulas An ionic formula the symbols and subscripts are written in the lowest whole-number ratio of the atoms or ions.  consists of positively and negatively charged ions  is neutral  Therefore has a charge balance total positive charge = total negative charge The symbol of the metal is written first, followed by the symbol of the nonmetal. 28  Charge Balance for NaCl, “Salt” In NaCl,  a Na atom loses its valence electron (metals loose e-)  a Cl atom gains an electron (nonmetals gains e-)  the symbol of the metal is written first, followed by the symbol of the nonmetal, ending in –ide.  Sodium Chloride Note that there is charge balance  Charge Balance In MgCl2 In MgCl2,  a Mg atom loses 2 valence electrons (Group 2; metals loose e-)  two Cl atoms each gain 1 electron (Group 17; metals gain e-)  subscripts indicate the number of ions needed to give charge balance Note that there is charge balance  Charge Balance in Na2S In Na2S,  2 Na atoms lose 1 valence electron each (group 1)  1 S atom gains 2 electrons (charge if group number – 18)  subscripts show the number of ions needed to give charge balance Note that there is charge balance EXAMPLE: Writing Ionic Formulas from Charges Charge balance is used to write the formula for sodium nitride, a compound containing Na+ and N3−. NaN X incorrect Na+ 3 Na+ + N3− = Na3N Na+ Na: metal (loose e-: group1  ion is 1+ 3(1+) + 1(3–) = 0 N: non-metal gain e- group 15 ion is 15-18 = 3- Formula from Ionic Charges Write the ionic formula of the compound containing Ba ions and Cl ions.  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 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 33  Study Check Select the correct formula for each of the following ionic compounds. 1. Na+ and O2− A. NaO B. Na2O C. NaO2 2. Al3+ and Cl− A. AlCl3 B. AlCl C. Al3Cl 3. Mg2+ and N3− A. MgN B. Mg2N3 C. Mg3N2  Solution Select the correct formula for each of the following ionic compounds. 1. Na+ and O2− B. Na2O Check: 2Na+ + O2− = 2(1+) + 1(2−) = 0 2. Al3+ and Cl− A. AlCl3 Check: Al3+ + 3Cl− = (3+) + 3(1−) =0 3. Mg2+ and N3− C. Mg3N2 Check: 3Mg2+ + 2N3− = 2(3+) + 2(3−) =0 Chapter 6 Compounds and Their Bonds Naming and Writing Ionic Formulas General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 36 REVIEW: Charges of Representative Elements General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 37  Naming Ionic Compounds When naming an ionic compound, the name of the metal is written first and is the same as the name of the element. the name of the nonmetal is the first syllable of the nonmetal name + ide ending and is written second. a space is placed between the name of the metal and nonmetal ion. Names of Some Common Ions General, Organic, and Biological Chemistry 39 Learning Check: Provide names for the following ions: Ba2+, Al3+ , K+ , N3 , O2 , F , P3 , S2 , Cl SOLUTION: Ba2+ Al3+ K+ barium ion aluminium ion potassium ion N3 O2 F nitride ion oxide ion fluoride ion P3 S2 Cl phosphide ion sulfide ion chloride ion 40 Naming Ionic Compounds with Two Elements To name a compound with two elements,  identify the cation and anion  name the cation first, followed by the name of the anion General, Organic, and Biological Chemistry 41 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 Al2S3 Al3+ S2– aluminum sulfide 42  Study Check Write the names of the following compounds. A. CaO ___________ B. Al2O3 ___________ C. MgCl2 ___________  Solution Write the names of the following compounds. STEP 1 Identify the cation and anion. A. CaO: The cation, Ca2+, is from Group 2A (2), and the anion, O2−, is from Group 6A (16). B. Al2O3: The cation, Al3+, is from Group 3A (13), and the anion, O2−, is from Group 6A (16). C. MgCl2: The cation, Mg2+, is from Group 2A (2), and the anion, Cl−, is from Group 7A (17).  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.  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.  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. Transition Metals Form Positive Ions Most transition metals and some Group 4(14) metals,  Form 2 or more positive ions  Zn2+, Ag+, and Cd2+ form only one ion. Metals with Variable Charge The names of transition metals with two or more positive ions (cations) use a Roman numeral after the name of the metal to identify ionic charge. Examples; Cu2+ copper(II) Pb2+ lead(II) Cu+ copper(I) Pb4+ lead(IV) Fe2+ iron(II) Cr2+ chromium(II) Fe3+ iron(III) Cr3+ chromium(III) Metals with Variable Charge Naming Ionic Compounds with Variable Charge Metals General, Organic, and Biological Chemistry 51  Determination of Variable Charge Use the charge on the anion and charge balance to calculate charge on the metal ion. MnF2 Mn is a transition metal F is a non-metal; gains with variable charge e-; charge is 18-17=-1 Mn charge + 2 F− charge =0 unknown? + 2 (1−) =0 2+ + 2− =0 Name: cation first with charge in (roman numerical) followed by anion ending in -ide Manganese(II) fluoride Examples of Names of Compounds with Variable Charge Metals General, Organic, and Biological Chemistry-- 53 Guide to Naming Ionic Compounds with Variable Charge Metals 54  Naming Ionic Compounds with Variable Charge Metals Name the ionic compound FeCl2. STEP 1 Determine the charge of the cation from the anion. Metal Nonmetal Formula FeCl2 ANALYZE THE Elements iron (Fe) and chloride (Cl) PROBLEM Groups transition element Group 7A (17) Ions 1 Fe unknown? 2 Cl− Charge 1 Fe ? + 2(1−) = 0 Balance 1(?) + 2(1−) = 0 Ions Fe2+ and Cl−  Naming Ionic Compounds with Variable Charge Metals Name the ionic compound FeCl2. STEP 2 Name the cation by its elemental name, and use a Roman numeral in parentheses for the charge. iron(II) STEP 3 Name the anion by using the first syllable of its element name followed by ide. chloride STEP 4 Write the name for the cation first and the anion second. iron(II) chloride  Naming of Cr2O3 Determine the charge of cation from the anion. Metal Nonmetal Formula Cr2O3 ANALYZE THE Elements chromium (Cr) oxide (O) PROBLEM Groups transition element Group 6A (16) Ions 2 Cr? 3 O2− Charge 2 Cr? + 3(2−) = 0 Balance 2(?) + 3(2−) = 0 Ions 2Cr3+ 3O2− Name cation by element name, and use a Roman numeral to show its charge  Cr3+ = chromium(III) Write the anion with an ide ending  oxide Name the cation first, then the anion  chromium(III) oxide 57 Guide to Writing Formulas from the Name 58 Writing Formulas Example 1: Write a formula for potassium sulfide Identify the cation and anion. Type of Ion Cation Anion ANALYZE Name Potassium sulphide THE Group Group 1A (1) Group 6A (16) PROBLEM Symbol of Ion K+ S2− Balance the charges K+ S2− K+ 2(1+) + 1(2–) = 0 Write the cation first. 2K+ and 1S2− = K2S1 = K2S 59 Writing Formulas Example 2:Write a formula for iron(III) chloride Identify the cation and anion. Type of Ion Cation Anion ANALYZE Name iron(III) chloride THE Group transition element Group 7A (17) PROBLEM Symbol of Ion Fe3+ Cl− Balance the charges. Fe3+ Cl− Cl− Cl− 1(3+) + 3(1–) = 0 Write the cation first. 1Fe3+ and 3Cl− = FeCl3  Study Check Write chemical formulas for the following compounds: A. nickel(II) sulfide B. zinc chloride C. iron(III) oxide  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+. The anion sulfide S2−. B. zinc chloride Zinc is one of the transition metals with a fixed charge of 2+, Zn2+. The anion chloride is Cl−. C. iron(III) oxide The Roman numeral (III) indicates that the charge on the iron ion is 3+, Fe3+. The anion oxide is O2−.  Solution Write chemical formulas for the following compounds. STEP 2 Balance the charges. A. nickel(II) sulfide C. iron(III) oxide Ni2+ S2− Fe3+ O2− 1(2+) + 1(2−) = 0 Fe3+ O2− O2− B. zinc chloride 2(3+) + 3(2−) = 0 Zn2+ Cl− Cl− 1(2+) + 2(1−) = 0  Solution Write chemical formulas for the following compounds. STEP 3 Write the formula, cation first, using subscripts from the charge balance. A. nickel(II) sulfide NiS B. zinc chloride ZnCl2 C. iron(III) oxide Fe2O3 Chapter 6 Compounds and Their Bonds Polyatomic Ions General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 65  Polyatomic Ions A polyatomic ion is a group of atoms has an overall ionic charge often consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen and oxygen. usually have a 1−, 2−, or 3− negative charge, except for NH4+, ammonium, which has a positive charge, Examples: NH4+ ammonium OH− hydroxide NO3− nitrate NO2− nitrite CO32− carbonate PO43− phosphate HCO3− hydrogen carbonate (bicarbonate) 66  Polyatomic Ions Many products contain polyatomic ions, which are groups of ions that have an ionic charge. 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 prefix hydrogen (or bi) HCO3− hydrogen carbonate (bicarbonate) HSO3− hydrogen sulfite (bisulfite) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 68 Names and Formulas of Common Polyatomic Ions 69 Some Compounds with Polyatomic Ions General, Organic, and Biological Chemistry 70 Guide to Writing formulas of Compounds with Polyatomic Ions Writing Formulas with Polyatomic Ions EXAMPLE 1: Aluminum Bicarbonate STEP 1 Identify the cation and polyatomic ion (anion). Cation Polyatomic ion Al3+ (Aluminium ion) HCO3− (bicarbonate ion) STEP 2 Balance the charges. From table 6.8 Al3+ HCO3− HCO3− HCO3− 1(3+) + 3(1−) = 0 STEP 3 Write the formula, cation first, using the subscripts from charge balance. Al(HCO3)3 Writing Formulas with Polyatomic Ions EXAMPLE 2: Sodium Phosphate STEP 1 Identify the cation and polyatomic ion (anion). Cation Polyatomic ion Na+ (sodium ion) PO43− (phosphate ion) STEP 2 Balance the charges. Na+ PO43− From table 6.8 Na+ Na+ 3(1+) + 1(3−) = 0 STEP 3 Write the formula, cation first, using the subscripts from charge balance. Na3(PO4)1 Writing as Na3PO4 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 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 74 Guide to Naming Compounds with Polyatomic Ions Naming Compounds with Polyatomic Ions When naming ionic compounds containing polyatomic ions, first write the positive ion, usually a metal. write the name of the polyatomic ion second. Recognizing polyatomic ions in a chemical formula helps to name it correctly. As with other ionic compounds, no prefixes are used.  Examples of Names of 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 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 77  Study Check Name the following ionic compounds: A. Ca(NO3)2 B. FePO4  Solution Name the following ionic compounds: STEP 1 STEP 2 STEP 3 STEP 4 Identify Name Name Name cation/anion cation anion compound Ca2+;NO3− calcium nitrate calcium nitrate Fe3+;PO43− iron(III) phosphate iron(III) phosphate