1 / 73

Chapter 5 Molecules and Compounds

Chapter 5 Molecules and Compounds. Sucrose molecule (sugar), contains C, H, and O atoms. However, the properties of sucrose are very different from those of C, H, and O alone. The properties of a compound are, in general, different from the properties of the elements that compose it.

grigg
Download Presentation

Chapter 5 Molecules and Compounds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 5 Molecules and Compounds Sucrose molecule (sugar), contains C, H, and O atoms. However, the properties of sucrose are very different from those of C, H, and O alone. The properties of a compound are, in general, different from the properties of the elements that compose it. molecular formula C12H22O11 2006, Prentice Hall

  2. CHAPTER OUTLINE

  3. LAW OF DEFINITECOMPOSITION • In a pure compound, the elements are always present in the same definite proportion by mass. • Based on this law, the mass of an element can be determined from its mass percent in a compound. % N in Sample 1 = % N in Sample 2 =

  4. Example 1: Barium iodide, BaI2, contains 35.1% barium by mass. How many grams of barium does an 8.50 g sample of barium iodide contain? 35.1 2.98 100 3 significant figures

  5. Example 2: When 12.66 g of calcium are heated in air, 17.73 g of calcium oxide is formed. What is the percent of oxygen in this compound? Mass of oxygen = 17.73 g – 12.66 g = 5.07 g Percent oxygen = 3 significant figures

  6. OCTET RULE& IONS • Most elements, except noble gases, combine to form compounds. Compounds are the result of the formation of chemical bonds between two or more different elements. • In the formation of a chemical bond, atoms lose, gain or share valence electrons to complete their outer shell and attain a noble gas configuration. • This tendency of atoms to have eight electrons in their outer shell is known as the octet rule.

  7. FORMATIONOF IONS • An ion (charged particle) can be produced when an atom gains or loses one or more electrons. Metals form cations A cation (+ ion) is formed when a neutral atom loses an electron 5.1

  8. FORMATIONOF IONS • An anion (- ion) is formed when a neutral atom gains an electron. Non-metals form anions 5.1

  9. IONIC CHARGES • The ionic charge of an ion is dependent on the number of electrons lost or gained to attain a noble gas configuration. • For most main group elements, the ionic charges can be determined from their group number, as shown below:

  10. Definition of Molecule and Compound • molecule -consist of at least two different atoms in a definite • arrangement held together by very strong chemical bonds. • compoundis a substance consisting of two or more elements in • fixed and definite proportions

  11. Formulas DescribeCompounds • a compound is a distinct substance that is composed of atoms of two or more elements • a compound can be described by the number and type of each atom in the simplest unit of the compound • molecules or ions • each element is represented by its letter symbol • the number of atoms of each element is written to the right of the element as a subscript

  12. Formulas Describe Compounds water = H2O \ two atoms of hydrogen and 1 atom of oxygen table sugar = C12H22O11\ 12 atoms of C, 22 atoms of H and 11 atoms O

  13. Order of Elements in a Formula • metals written first • NaCl • nonmetals written in order from Table 5.1 • CO2 • there are occasional exceptions for historical or informational reasons • H2O fits rule, but does NaOH? Tro's Introductory Chemistry, Chapter 5

  14. Types of Chemical Formulas • An empirical formula gives the relative number of atoms of each element in a compound. • A molecular formula gives the actual number of atoms of each element in a molecule of the compound. • For example, the molecular formula for hydrogen peroxide is H2O2, and its empirical formula is HO. • The molecular formula is always a whole number multiple of the empirical formula. • For many compounds, such as H2O, the molecular formula is the same as the empirical formula. • A structuralformula uses lines to represent chemical bonds and shows how the atoms in a molecule are connected to each other.

  15. Comparison of Formulas and Models for Methane, CH4 • The molecular formula of methane indicates that methane has 1 carbon atom and 4 hydrogen atoms. • The structural formula shows how the atoms are connected: each hydrogen atom is bonded to the central carbon atom. • The ball-and-stick model and the space-filling model illustrate the geometry of the molecule: how the atoms are arranged in three dimensions.

  16. Classifying Materials • atomic elements = elements whose particles are single atoms • molecular elements = elements whose particles are multi-atom molecules • molecular compounds = compounds whose particles are molecules made of only nonmetals • ionic compounds = compounds whose particles are cations and anions Tro's Introductory Chemistry, Chapter 5

  17. Molecular Elements • Certain elements occur as 2 atom molecules • Rule of 7’s • there are 7 common diatomic elements • find the element with atomic number 7, N • make a figure 7 by going over to Group 7A, then down • don’t forget to include H2 VIIA 7 H2 N2 O2 F2 Cl2 Br2 I2

  18. Molecular Compounds • two or more nonmetals • smallest unit is a molecule

  19. Ionic Compounds • metals + nonmetals • no individual molecule, instead these have 3-dimensional array of cations and anions made of formula units (NaCl)

  20. Metal Nonmetal IONICCOMPOUNDS • After bonding, each atom achieves a complete shell (noble gas configuration). • Ionic bonds occur between metals and non-metals. • Ionic compounds contain ionic bonds, which occur when electrons are transferred between two atoms.

  21. IONICCOMPOUNDS • Atoms that lose electrons (metals) form positive ions (cations). • Atoms that gain electrons (non-metals) form negative ions (anions). • The smallest particles of ionic compounds are ions (not atoms). Anion Cation

  22. IONIC CHARGESAND FORMULAS • The formula of an ionic compound indicates the number and kinds of ions that make up the ionic compound. • The sum of the ionic charges in the formula is always zero, which indicates that the total number of positive charges is equal to the total number of negative charges. • For example, the +1 charge on the sodium ion is cancelled by the –1 charge on the chloride ion, to form a net zero charge. (1+) + (1) = 0 loses 1 e gains 1 e

  23. IONIC CHARGESAND FORMULAS • When charges between the two ions do not balance, subscripts are used to balance the charges. • For example, since each magnesium loses 2 electrons, and each chloride gains one electron, 2 chlorides are needed to balance the charge of the magnesium ion. • Therefore magnesium chloride is written as MgCl2. MgCl2 loses 2 e Each gains 1 e (2+) + 2(1) = 0

  24. Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound • aluminum, Al • aluminum chloride, AlCl3 • chlorine, Cl2 • acetone, C3H6O • carbon monoxide, CO • cobalt, Co = atomic element = ionic compound = molecular element = molecular compound = molecular compound = atomic element

  25. TYPES OF COMPOUNDS • Compounds can be classified as one of two types: • Compounds are pure substances that contain 2 or more elements combined in a definite proportion by mass. Two non-metals Metals and non-metals

  26. Common Names – Are Exceptions(like nicknames) Nomenclature of Compounds H2O = water, steam, ice NH3 = ammonia CH4 = methane NaCl = table salt C12H22O11 = table sugar

  27. Metal Cations • Type I • metals whose ions can only have one possible charge • IA, IIA, (Al, Ga, In) • determine charge by position on the Periodic Table • IA = +1, IIA = +2, (Al, Ga, In = +3) • Type II • metals whose ions can have more than one possible charge • determine charge by charge on anion How do you know a metal cation is Type II? its not Type I !!!

  28. BINARY IONICCOMPOUNDS (TYPE I) • Binary compounds contain only two elements. • Ionic compounds are formed by combination of a metal and a non-metal. • Type I ions are those cations that form only one ion. • In these compounds, charges of the cations must equal the charges of the anions since the net charge is zero.

  29. BINARY IONICCOMPOUNDS (TYPE I) • Subscripts are used to balance the charges between cations and anions. sodium bromide potassium sulfide Na+ Br K+ K2+ S2 +2-2= 0 No subscripts needed +1-1 = 0 +1-2 0 NaBr K2S

  30. Example 1: Write formulas for the following ionic compounds: calcium chloride sodium sulfide Na2+ Na+ S2 Ca2+ Cl Cl2 +2-2= 0 +2-2= 0 +2-1 0 +1-2 0 Na2S CaCl2

  31. Type I Binary Ionic Compounds • Contain Metal Cation + Nonmetal Anion • Metal listed first in formula & name • name metal cation first, name nonmetal anion second • cation name is the metal name • nonmetal anion named by changing the ending on the nonmetal name to -ide

  32. BINARY IONICCOMPOUNDS (TYPE I) MgCl2 magnesium chloride sodium iodide NaI AlF3 aluminum fluoride

  33. Example 2: Name the following ionic compounds: Na3P sodium phosphide BaCl2 barium chloride

  34. BINARY IONICCOMPOUNDS (TYPE II) • Type II ions are those cations that form more than one ion. • When naming compounds formed from these ions, include the ionic charge as Roman numeral, in parentheses, after the metal’s name. • This method of nomenclature is called the “stock” system.

  35. NAMING AND WRITINGIONIC FORMULAS • When writing ionic formula, knowing the charge of the ions are important since the net charge on the compound must be zero. • Some elements produce only one ion (Type I) while others produce two or more ions (Type II). • Differentiating between type I and II ions is important, since the naming system is different for each. Shown below are the common ions of each type: Type I Type II

  36. BINARY IONICCOMPOUNDS (TYPE II) • name metal cation first, name nonmetal anion second • metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge (only difference from type II!) • determine charge from anion charge • nonmetal anion named by changing the ending on the nonmetal name to -ide

  37. BINARY IONICCOMPOUNDS (TYPE II) +2 -1 ? -1 FeCl2 iron (II) chloride ? -2 = 0 +3 -1 ? -1 FeCl3 iron (III) chloride ? -3 = 0

  38. BINARY IONICCOMPOUNDS (TYPE II) +1 -2 ? -2 copper (I) oxide Cu2O 2? -2 = 0 Roman numeral DOES NOT represent the subscript +2 -2 ? -2 copper (II) oxide CuO ? -2 = 0

  39. BINARY IONICCOMPOUNDS (TYPE II) • Type II cations can also be named by an older method (classical). • In this system, cations with the higher charge end in –ic, while cations with the lower charge end in –ous. • In this system, some cations are named based on their Latin roots.

  40. CLASSICAL SYSTEM (DERIVED FROM LATIN) gold (aurumfor Aurora the Roman goddess of the dawn) silver (argentumfor 'bright') copper (cuprumfor 'Cyprus' where the Romans first obtained copper) tin (stannumfor alloys containing lead) lead (plumbumfor 'lead') mercury (hydrargyrumfor 'liquid silver' or quick silver) antimony (stibiumfor 'not alone') iron (ferrumfor 'firmness‘) potassium (kalium via the Arabic qali for alkali) sodium (natrium for soda)

  41. BINARY IONICCOMPOUNDS (TYPE II) +2 -1 FeCl2 ferrous chloride Higher charge Lower charge +3 -1 FeCl3 ferric chloride

  42. BINARY IONICCOMPOUNDS (TYPE II) +1 -2 Cu2O cuprous oxide Higher charge Lower charge +2 -2 CuO cupric oxide

  43. Example 1: Name each of the following compounds using the stock and classical nomenclature system: Stock +2 -1 ? -1 tin (II) chloride SnCl2 Classical ? -2 = 0 Lower charge stannous chloride

  44. Example 1: Name each of the following compounds using the stock and classical nomenclature system: Stock +1 -2 ? -2 copper (I) sulfide Cu2S 2? -2 = 0 Lower charge Classical cuprous sulfide

  45. Example 2: Write formulas for each of the following compounds: +2 -1 Tin (II) bromide Sn Br Br2 +2 -1  0 +2 -2 = 0 SnBr2

  46. Example 2: Write formulas for each of the following compounds: +4 -2 Stannic oxide Sn O O2 +4 -2  0 +4 - 4 = 0 SnO2

  47. ExamplesWhat, if anything, should go into the parenthesis • LiCl = lithium ( ) chloride • AlCl3 = aluminum ( ) chloride • PbO = lead ( ) oxide • PbO2 = lead ( ) oxide • Mn2O3 = manganese ( ) oxide X X II IV III

  48. POLYATOMIC IONS • Some ionic compounds contain polyatomic ions, an ion composed of several atoms bound together.

  49. Patterns for Polyatomic Ions • elements in the same column form similar polyatomic ions • same number of O’s and same charge ClO3- = chlorate \ BrO3- = bromate 2. if the polyatomic ion starts with H, the name adds hydrogen- prefix before name and add 1 to the charge CO32- = carbonate \ HCO3-1 = hydrogencarbonate

  50. -3 -2 -1 BO CO NO 3 3 3 -2 -3 -2 -1 SiO PO SO ClO 3 4 4 3 -3 -2 -1 AsO SeO BrO 4 4 3 -2 -1 TeO IO 4 3 Periodic Pattern of Polyatomic Ions-ate groups IIIA IVA VA VIA VIIA

More Related