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Chapter 5

Chapter 5. Molecules and Compounds. Homework. Assigned Problems (odd numbers only) Required “Problems” 23-79 (odd) “Cumulative Problems” 81-97 (odd) Highlight Problems “Highlight Problems” 99, 101 (odd). Compounds Display Constant Composition.

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Chapter 5

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  1. Chapter 5 Molecules and Compounds

  2. Homework • Assigned Problems (odd numbers only) • Required • “Problems” 23-79 (odd) • “Cumulative Problems” 81-97 (odd) • Highlight Problems • “Highlight Problems” 99, 101 (odd)

  3. Compounds Display Constant Composition • Compounds are pure substances consisting of two or more elements held together by a chemical bond • A compound can be broken into its elements by a chemical process • The percentage of each element in a specific compound does not vary • The Law of Definite Proportions (Constant Composition): In a pure compound, the elements are always present in the same definite proportions by mass

  4. Compounds Display Constant Composition Example: • Two samples of ammonia gas with different sample masses • Upon decomposition, the mass ratios of nitrogen to hydrogen are the same Sample 1: Sample 2:

  5. Chemical Formulas: How to Represent Compounds • Chemical formulas are a concise way of stating a specific chemical compound’s composition • The notation contains the symbols of the elements present and the subscripts to indicate the number of atoms per element in a structural unit of the compound Aspirin’s chemical formula is C9H8O4 Element symbols subscripts 21 atoms are present: 9 carbon atoms, 8 hydrogen atoms, and 4 oxygen atoms Ratio of C to H to O is 9:8:4

  6. Chemical Formulas: How to Represent Compounds Co is the symbol for cobalt CO is the formula for carbon monoxide sodium chloride NaCl not ClNa carbon dioxide CO2 not O2C All pure samples of a compound have the same composition If only one atom is present in a molecule, the subscript “1” is omitted Follow the capitalization rules for elemental symbols When writing formulas, list the metal or most metallic element first

  7. Chemical Formulas: How to Represent Compounds • If a chemical formula contains groups of atoms in parentheses, the subscript following the parentheses indicates the number polyatomic units in the formula • Number of atoms is determined by multiplying the subscript outside the parenthesis by the subscript for every atom inside the parenthesis • Composition is 1 Mg atom, 2 N atoms, 6 O atoms Polyatomic ion

  8. A Molecular View ofElements and Compounds • Pure substances • Elements • Atomic • Molecular • Compounds • Ionic • Molecular

  9. Elements and Compounds • Elements are substances that cannot be decomposed into simpler substances • Each element is composed of only one type of atom • Most elements are atomicelements and exist as single atoms (monatomic) • Molecular elements are found naturally as two or more of the same type of atom bound together (diatomic)

  10. Elements and Compounds • A compound can be decomposed into two or more simpler substances • The ultimate breakdown products are elements • Two types of compounds • Molecular • Ionic

  11. Molecular Compounds • A molecule is a group of two or more atoms bound together as a unit • A molecular compound involves a bond between two or more nonmetals • Bonds occur between different or identical atoms • The individual molecule is the smallest particle that can exist as a stable, independent unit of the compound

  12. Molecular (Covalent) Compounds • Molecular compounds are compounds composed of molecules that exist as the individual structural unit • The simplest molecule contains two atoms (diatomic). They can be the same or different atoms • Next in complexity are triatomic and tetraatomic O2 oxygen O3 ozone A diatomic molecule A triatomic molecule CO carbon monooxide H2O water A diatomic molecule A triatomic molecule

  13. Ionic Compounds • Ionic compounds are compounds which are held together by the attraction of positive and negative ions • Solid crystals formed by a very ordered packing of oppositely charged ions • Most ionic compounds are composed of a metal and a nonmetal • High melting temperatures

  14. Ionic Compounds • Solids • They do not exist as single molecules • The chemical formula represents the simplest ratio that these atoms combine together • Held strongly together, these ions are packed together into a “lattice” • Each Na+ ion is surrounded on each side by Cl- ions • Each Cl- ion is surrounded on each side by Na+ ions Formula unit = NaCl

  15. Ionic Compoundsvs. Molecular Compounds • For molecular compounds, the chemical formulas give the composition of the molecules • For ionic compounds, the chemical formulas give the ion ratio within the compound

  16. Writing Formulas for Ionic Compounds (Charge Balance in Ionic Compounds) • Binary ionic compounds are composed of only two elements (metal and nonmetal) • The symbol of the cation always precedes the symbol of the anion • The sum of the positive charges (cation) must equal the sum of the negative charges (anion) • Net charge is zero (charge-neutral) • Subscripts written as whole numbers indicate the number of each ion in the formula unit

  17. Sodium Chloride Formed from sodium and chlorine atoms An ionic bond forms consisting of a sodium ion (+ charge) and a chloride ion (- charge) Each sodium loses one electron to achieve an octet Each chlorine atom gains one electron to achieve an octet Formula is NaCl Writing Formulas for Ionic Compounds Subscripts in Formulas

  18. Magnesium Chloride Formed from magnesium and two chlorines An ionic bond forms consisting of a magnesium ion (2+ charge) and two chloride ions (- charge each) Each magnesium loses two electrons to achieve an octet Each chlorine atom gains one electron to achieve an octet Formula is MgCl2 Writing Formulas for Ionic Compounds Subscripts in Formulas

  19. Writing Ionic Formulas for Ionic Charges • Subscripts in a formula represent the number of positive and negative ions • Write the formula for the ionic compound containing Na+ and N3- Na• Na+ • • Na• N 3- • •• N Na+ • • •• •• • • •• •• •• • • • Na+ Na• Gains 3e- • • • Net charge: 3(1+) + 1(3-)=0 Formula:Na3N Each loses 1e-

  20. Naming Ionic Compounds For ionic compounds containing two elements: • Compounds containing a metal and a nonmetal are called binary ionic compounds • Two types of metals: • Single Cation Metals: Form one positive ion • Multiple Cation Metals: Form more than one positive ion • The systematic naming uses the name of the cation first, followed by the name of the anion • Subscripts in the formula are not included in the name

  21. Types of Metal Ions • Single Cation Metals (Type I) • Form only one type of ion (one possible charge) • Main group metals in groups IA, IIA, and some IIIA • e.g. Sodium only forms one ion (Na+)in chemical reactions • Determine charge by position on the periodic table (also see table 5.3 on page 136)

  22. Types of Metal Ions • Single Cation Metals (Type I) • Form only one type of ion (one possible charge) • Main group metals in groups IA, IIA, and some IIIA • e.g. Sodium only forms one ion (Na+)in chemical reactions • Determine charge by position on the periodic table (also see table 5.3 on page 136)

  23. Types of Metal Ions • Multiple Cation Metals (Type II) • Form two or more types of ions (variable possible charge) • Transition metals in groups 3B to 12B, and some 4A and 5A • For example, iron forms two ions (Fe2+ and Fe3+) in chemical reactions • Determine charge by the “stock system” for naming ions • The metal name followed by a Roman numeral in parentheses to indicate its charge (see table 5.4 on page 136)

  24. Types of Metal Ions • Multiple Cation Metals (Type II) • Form two or more types of ions (variable possible charge) • Transition metals in groups 3B to 12B, and some 4A and 5A • For example, iron forms two ions (Fe2+ and Fe3+) in chemical reactions • Determine charge by the “stock system” for naming ions • The metal name followed by a Roman numeral in parentheses to indicate its charge (see table 5.4 on page 136)

  25. Naming Type I Binary Ionic Compounds • Compounds which contain a positively charged metallic ion and a negatively charged nonmetallic ion • Name metal cation first, name nonmetal anion second • Single metal cation name is the metal name only, drop the word “ion” • Nonmetal anion named by changing the ending on the nonmetal name to -ide Name of metal__base name of nonmetal + -ide

  26. Naming Type I Ionic Compounds • KCl • Potassium Chloride • Na3P • Sodium Phosphide • Rb2S • Rubidium Sulfide • Mg3N2 • Magnesium Nitride • NaI • Sodium Iodide • CaF2 • Calcium Fluoride • Li2O • Lithium Oxide • AgCl • Silver Chloride

  27. Naming Type II Binary Ionic CompoundsMultiple Cation Metal Compounds • Metal listed first in formula & name (same order as for Type I compounds) • Determine metal cation charge from the anion charge • Common multiple cations in Table 5.4, page 136

  28. Naming Type II Binary Ionic CompoundsMultiple Cation Metal Compounds • Use the metal name (cation) first, followed by a Roman numeral in parentheses to indicate its charge • Nonmetal anion named by changing the ending on the nonmetal name to -ide Name of metal (charge of metal)______base name of nonmetal + -ide cation anion

  29. Naming Type II Binary Ionic Compounds • FeI3 • 1(?)+3(-1)=0 • Iron (III) Iodide • Cu2O • 2(?)+1(-2)=0 • Copper (I) Oxide • SnBr2 • 1(?)+2(-1)=0 • Tin (II) Bromide

  30. Naming Type II Binary Ionic Compounds Determining the Charge of the Cation from the Anion • Determine the charge of Cu in Cu2O • Write the name of the compound • Determine the charge of the cation from the anion • Cu2O - the nonmetal anion is O, since it is in Group 6A, its charge is 2- • Since there are 2 Cu ions in the formula and the total positive charge is 2+, divide by the number of cations so each Cu has a 1+ charge

  31. Naming Type II Binary Ionic Compounds Determining the Charge of the Cation from the Anion • Name the cation by its element name and use a Roman numeral in parenthesis to indicate its charge • Copper (I) • Name the anion by changing the last part of its element name to –ide • Oxygen • Write the name of the cation first and the name of the anion second oxide copper (I) oxide

  32. Naming Type II Binary Ionic Compounds Determining the Charge of the Cation from the Anion • SnI4 • 1(?)+4(-1)=0 • Tin (IV) iodide • HgO • 1(?)+1(-2)=0 • Mercury (II) Oxide • MnCl2 • 1(?)+2(-1)=0 • Manganese (II) Chloride

  33. Writing Formulas from the Name of an Ionic Compound • Usually involves a metal and a nonmetal • Identify the cation and the anion • Balance the charges to write the formula • If it is a multiple cation metal, the Roman numeral determines the charge of the cation • When writing the formula, take the name of the cation first, followed by the name of the anion

  34. Writing Formulas from the Name of an Ionic Compound • Compound name is lithium chloride • Li+ and Cl- are the ions • Balance the charges • Write the formula • LiCl is the formula using the subscripts from the charge balance 1 1

  35. Writing Formulas from the Name of an Ionic Compound • Compound name is iron (III) oxide • Fe3+ and O2- are the ions • Balance the charges • Write the formula • Fe2O3is the formula using the subscripts from the charge balance 2 3

  36. Polyatomic Ions • Polyatomic ions are a group of atoms covalently bonded together into a single unit • The unit obtains a charge • Most PA ions are negatively charged • Oxyanions (anions): P, S, C, or N covalently bound to one or more oxygens • Never occur independently, always associated with ions of opposite charge • Only one PA is positively charged • ammonium ion

  37. Naming Ionic Compounds Containing a Polyatomic Ion • Must memorize name, formula and charge (Table 5.6 on page 138). Look for relationships between ions • Most PA ions are oxyanions: The number of oxygen atoms bonded to the same element (e.g. P, S, or N) will determine the name (suffix) of the ion • ~ate is most common • ~ite has one less oxygen bonded

  38. Naming Ionic Compounds Containing a Polyatomic Ion • ~ate, ~ite pairs of ions • The ion in the pair with the most oxygens is always the ~ate ion • The ion in the pair with one less oxygen is always the ~ite ion • Ion pair with a 3- charge • phosphate (PO43-), phosphite (PO33-) • Ion pair with a 2- charge • sulfate (SO42-), sulfite (SO32-) • Ion pair with a 1- charge • nitrate (NO3-), nitrite (NO2-)

  39. Naming Ionic Compounds Containing a Polyatomic Ion • Group 7A elements can form more than two types of polyatomic ions (oxyanions) • Additional prefixes are used to differentiate the ions • See page 138-9 (class text) and page 330 (lab text) • The number of oxygens attached to the central atom has an effect on the name of the ion • e.g. Polyatomic ions of chlorine, bromine and iodine

  40. Naming Ionic Compounds Containing a Polyatomic Ion (Group VIIA) • Example: Polyatomic ions of chlorine • -ate ion • chlorate = ClO3- • -chlorate ion with 1 more O than chlorate, use per- prefix • perchlorate = ClO4- • - chlorate ion with 1 less O, use -ite suffix • chlorite = ClO2- • -chlorite ion with 1 less O, use hypo- prefix • hypochlorite = ClO-

  41. Naming Ionic Compounds Containing a Polyatomic Ion • Named the same way as binary ionic compounds • Positive ion (metal) name is written first • Polyatomic ions name follows the metal • No prefixes are used in the name • Cation: Check to see if metal is single or multiple cation • Use the name of the PA ion given in table 5.6 on page 138

  42. Naming Ionic Compounds Containing a Polyatomic Ion • CaSO4 • calcium sulfate • Ca2+ and SO42- • Li2CO3 • lithium carbonate • Li+, CO32- • Al(NO3)3 • aluminum nitrate • Al3+, NO3-

  43. Writing Formulas for Compounds Containing a Polyatomic Ion • Formulas are written like binary ionic compounds • Consider polyatomic ions as single units with a certain charge • Obtain the correct ratio of cation to anion to achieve a net charge of zero • Use parentheses if more than one of the same PA unit is needed in a formula • Use subscripts to indicate the number of a particular ion in a formula

  44. Writing Formulas for Compounds Containing a Polyatomic Ion • Compound name is magnesium carbonate • Mg2+ and CO32- are the ions • Balance the charges • Write the formula • MgCO3 is the formula using the subscripts from the charge balance 1 1

  45. Writing Formulas for Compounds Containing a Polyatomic Ion • Compound name is calcium nitrate • Ca2+ and NO3- are the ions • Balance the charges • Write the formula • Ca(NO3)2 is the formula using the subscripts from the charge balance 1 2

  46. Writing Formulas for Compounds Containing a Polyatomic Ion • Compound name is iron (III) sulfate • Fe3+ and SO42- are the ions • Balance the charges • Write the formula • Fe2(SO4)3 is the formula using the subscripts from the charge balance 3 2

  47. Writing Formulas for Compounds Containing a Polyatomic Ion • Compound name is ammonium phosphate • NH4+ and PO43- are the ions • Balance the charges • Write the formula • (NH4)3PO4is the formula using the subscripts from the charge balance 3 1

  48. Naming Molecular Compounds • Molecular binary compounds • Composed of two nonmetal elements • Naming a compound • Use the full (element ) name for the first nonmetal • Add the –ide ending to the full name of the second nonmetal • Second nonmetal named like the nonmetal in binary ionic compounds (anion) • Indicate the number of atoms by adding numerical prefixes

  49. Prefixes Used in Naming Molecular (Covalent) Compounds (page 140)

  50. Naming Molecular Compounds Prefix- Name of 1st nonmetal ___Prefix- Name of 2nd nonmetal + -ide • In ionic compounds the subscripts are not mentioned in the name • Many compounds can exist for many pairs of nonmetallic elements (e.g. nitrogen and oxygen) BaCl2 barium chloride barium dichloride Na2SO4 sodium sulfate disodium sulfate nitrogen monoxide nitrogen dioxide dinitrogen monoxide

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