1. Quarter 2 Unit 4

2. Compounds and Atomic Stability: Learning Objectives Understand why atoms form compounds Understand chemical stability and the octet rule Understand how Ionic bonds and Ionic compounds are formed

3. How Elements Form Compounds Compounds: a chemical combination of two or more different elements joined together in a fixed proportion Collisions between particles of the atom cause reactions Reactions between atoms Involve Only The Electron Cloud! Remember, chemical properties of elements on the periodic table repeat because the pattern of valence electrons repeat in each period Valence electrons of colliding atoms react to form compounds Compounds form when electrons in atoms rearrange to achieve stable electron configurations.

4. Chemical Stability Nobel Gasses: they are almost completely un-reactive None of these have ever been found naturally in the environment as a compound. They are extremely un-reactive or stable Group 18 (except He) all have 8 valence electrons Electron arrangement determines chemical properties The electron arrangement of the noble gasses is the cause of their stability (extremely un-reactive)

5. Check Your Understanding Turn and discuss the following with the person on your right, then answer each of the questions in your notebook. 1. Identify each of the following as a compound or not a compound a. Water b. Nitrogen c. Carbon dioxide d. Deuterium 2. What subatomic particles are involved in forming compounds? 3. Why do elements form compounds? 4. Which group of elements rarely forms compounds? Explain why.

6. Answers 1. Identify each of the following as a compound or not a compound a. Water--- compound b. Nitrogen---- no, an element c. Carbon dioxide-----compound d. Deuterium-----no, an element 2. What subatomic particles are involved in forming compounds?--- valence electrons 3. Why do elements form compounds? --To rearrange electrons in order to achieve a stable electron configuration 4. Which group of elements rarely forms compounds? Explain why. ---Noble gasses, because they already have a stable electron configuration

7. The Octet Rule Atoms combine to become more stable Atoms become stable by having eight electrons in their outer energy levels (He is an exception w/ 2 because it is so small) Atoms become stable by achieving a noble gas configuration

8. Achieving Chemical Stability Collisions between atoms, which involve enough energy, can cause valence electron rearrangements Forming a stable octet Noble gas configuration Total number of electrons never change

9. Establishing Stable Octets 2 options 1. Transfer of electrons between atoms 2. Sharing electrons between atoms

10. Electrons are Transferred Example Na- sodium is a shiny gray metal which quickly oxidizes upon exposure to the atmosphere Cl - Chlorine gas is a dense, pale yellowish-green, poisonous, gas Na and Cl react to form–salt

11. Electron Transfer On a Subatomic Level Na- a group 1 element, with 1 valence electron Cl - a group 17 element, with 7 valence electrons How can the valence electrons be rearranged to provide a stable octet for each?

12. Chlorine Gets a Stable Octet If the Cl atom gains an electron from the Na atom, it will achieve a noble gas configuration It will be stable It will have a complete octet It will also have a negative charge, because it has an extra electron It will be an ion

13. Na Gets a Stable Octet If Na gives away its 1 valence electron, what will it have for a valence number? 11 electrons minus 1 electron = 10 electrons 1 s 2 2 s 2 2 p 6 - 8 valence electrons It will be stable It will have a complete octet It will also have a positive charge, because it has one less electron It will be an ion

14. Transfer of the Electron Forms an Ionic Bond

15. An Ionic Bond The exchange of the electron creates 2 ions, 1 positively and 1 negatively charged Ionic bond: A strong attractive force between atoms with opposite charges which is formed by an electron transfer between atoms. Ionic bonds form ionic compounds A compound that is made up of ions Na+ Ions are attracted to all nearby Cl- Ions and visa versa thereby forming crystal structures Cl- Na+

16. The Results of Ionic Attraction Affects properties of the compound Example; sodium chloride (salt) is a crystal because of intermolecular forces of attraction between ions, it is a solid at room temperature Melting Ionic Compounds: Breaking the strong crystal structure requires a lot of energy, therefore the melting point of NaCl is more than 800°C Hardness and Brittleness: It takes a great deal of force to break the structure of an ionic crystal

17. Naming Binary Ionic Compounds Binary compounds are compounds with only two different elements. 1. First write the name of the positively charged ion (usually a metal) 2. Then add the name of the negatively charged ion (nonmetal) 3. Modify the negatively charged ion name to end in -ide 1. Example NaCl is called sodium chloride NOT sodium chlorine

18. Check Your Understanding Name compounds formed by the following ions: 1. Mg+ Cl- 2. Cl- Ca+ 3. Cl- K+ Name these compounds: 1. AlN 2. KI 3. ZnO

19. Answers Name compounds formed by the following ions: 1. Mg+ Cl- Magnesium chloride 2. Cl- Ca+ calcium chloride 3. Cl- K+ potassium chloride Name these compounds 1. AlN aluminum nitride 2. KI potassium iodide 3. ZnO zinc oxide

20. Oxidation Numbers Charged atoms or compounds are called Ions The total charge on the ion is known as the Oxidation Number of the atom Examples: Mg +2 is magnesium ion, the charge is positive 2, the oxidation number is 2+ F- has an oxidation number of 1- Some metals have the same oxidation number in all compounds (memorize this) Group 1 elements, oxidation number = 1+ Group 2 elements, oxidation number = 2+ Aluminum, oxidation number = 3+

21. The Charge of Ionic Compounds In Ionic Compounds, the total positive charge is equal to the total negative charge One Mg 2+ ion will combine with 2 Cl - ions Forming MgCl 2, The total positive charge is 2+, the total negative charge is 2- +2+-2 = 0 In a correctly written formula, the sum of the total positive charges and the total negative charges = 0

22. Predicting Oxidation Numbers Oxidation numbers for most elements can be predicted from their position on the periodic table. Groups 3-12 Transition metals are difficult as many of these elements Have more than one oxidation number depending on the reaction Group 13 elements have 3 valence electrons, so will lose 3 and have an oxidation number of 3+ Group 14 may have 2+ or 4+ oxidation number Groups 15, 16 and 17 tend to gain electrons to complete the octet since they are already ½ full Their oxidation numbers are 3-, 2-, and 1- respectively They can also lose electrons and have positive oxidation numbers The tendency to lose electrons increases as you move down the column

23. Check for Understanding Predict the oxidation numbers for the following elements: 1. Al 2. N 3. Cl 4. Mg 5. S 6. Na 7. K 8. O 9. Ga 10. P 11. Se 12. Br

24. Answers Predict the oxidation numbers for the following elements: 1. Al 3+ 2. N 3- 3. Cl 1- 4. Mg 2+ 5. S 2- 6. Na 1+ 7. K 1+ 8. O 2- 9. Ga 3+ 10. P 3- 11. Se 2- 12. Br 1-

25. Writing Chemical Formulas For Ionic Compounds The key to writing formulas is to make the oxidation numbers add to zero, making a neutral compound. Example: Ca 2+, located in group 2 F 1-, located in group 17 The formula for a compound of these elements is CaF 2 1(2+) + 2( 1-) =0 The compound is neutral

26. Representing Compounds as Formulas The formula of a compound tells: what elements make up the compound and how many of each element are present in one unit of the compound Example : H2O two H for each O

27. Progress Check Write formulas for the following compounds: 1. Sodium Fluoride 2. Potassium Chloride 3. Rubidium bromide 4. Sodium selenide 5. Potassium oxide 6. Lithium sulfide 7. Strontium fluoride 8. Calcium Chloride

28. Answers Write formulas for the following compounds: 1. Sodium Fluoride (Na+1 F-1) NaF 2. Potassium Chloride (K+1 Cl -1) KCl 3. Rubidium bromide (Rb+1 Br-1) RbBr 4. Sodium selenide (Na +1 Se -2) Na2Se 5. Potassium oxide (K+1 O-2) K2O 6. Lithium sulfide (Li+1 S -2) Li2S 7. Strontium fluoride (Sr 2+ F 1-) SrF2 8. Calcium Chloride (Ca 2+ Cl 1-) CaCl2

29. The Formation Of Ionic Compounds Lab Learning Objective: To model the transfer of electrons thereby achieving noble gas configurations and the formation of stable ionic compounds Apply what you have learned! The Formation Of Ionic Compounds (MiniLab 4.2) Question: What other atoms give up and gain electrons (creating ions, forming ionic bonds) to form ionic compounds?

30. Pre-Lab Procedure 1. You and your lab partner must locate the following atoms on the periodic table: Li, S, Mg, O, Ca, N, Al and I. 2. Using the information on the Periodic Table, and what you have learned, complete the table with the Valence electrons, class of element, Lewis dot diagram, and electron configuration for the given atoms 3. Based on what you have discovered about the atoms above, construct a hypothesis predicting which of the atoms will give up electron(s) and which will receive electron(s) when forming compounds. REMEMBER a hypothesis is an if… then… statement which answers the lab question 4. Have your hypothesis checked before you begin the lab.

31. The Formation Of Ionic Compounds Learning Objectives: To model the transfer of electrons thereby achieving noble gas configurations and the formation of stable ionic compounds To name ionic compounds To identify formulas of ionic compounds Identify a pattern which can be used to predict which atoms will form Ionic compounds Follow the Lab instructions to complete your investigation. Prepare for a poster presentation

32. Polyatomic Ions Some Ions are formed by more than one or two types of atoms They are called polyatomic ions Some of these are very common, so recognizing them will be very helpful to you. Let’s look at some Some do not follow simple naming rules, often because they were named before rules for naming were written These we need to use a reference sheet for, or memorize! Use your reference sheets to help name complex polyatomic ionic compounds

33. Conventions for Naming Polyatomic Ionic Compounds When Given the Formula Steps 1. Name positive ion (cation) first, then negative ion (anion) second. A. If one of these ions has more than 1 atom in it, look up the name on the chart i. You should plan on memorizing the ones I have starred! 2. Determine if you need a Roman numeral in the name A. If cation is NOT a transition metal, then NO Roman numeral B. If the cation is a transition metal then see if it can have more than 1 oxidation number, if not then go to step 4 C. If yes then go to step 3 3. Determining the Roman numeral, usually the number of anions = the charge on the cation and the number of cations =anions. 1. Example: Fe2[SO4}3 1. There are three SO4 sulfate ions -- charge of 2-= 6 - 2. There are two Fe atoms – charge of ? = must total 6 1. Fe has to be 3+ so use Roman Numeral III  Fe(III) 2. Name is Iron (III) sulfate! 4. Check to see that the sum of oxidation numbers= 0 1. If yes then correct! 1. Example : 1. 3, SO4 ions = 3 x 2- = 6- 2. 2 Fe(III) ions = 2 x 3+ = 6+ 3. 6- + 6+ = 0 !!!!!

34. Let’s Try Another One NH4Cl Look at your list of common polyatomic ions, do you see any here? Yes NH4 is ammonium it is a cation – 1+ Follow step 1--- Ammonium is the first part of the name Chlorine is the second atom, the anion- 1-, becomes chloride (just like before) So far we have ammonium chloride Follow step 2--- Is ammonium a transition metal? No! Follow step 4 1+ + 1- = 0 correct!  ammonium chloride

35. Now you try it alone! Name the following : Fe(NO3)3

36. Solution Iron(III)nitrate Iron  cation = 2+ or 3+ NO3  nitrate = 1- Three anions, so the charge needs to be 3+ so Roman numeral is III Check 1 Fe(III) has charge of 3+ 3 NO3 ions have a charge of 3 x 1- = 3- 3+ + 3- = 0 correct!  Iron(III)nitrate

37. Let’s Try Another Al(CN)3

38. Answer Al(CN)3 Aluminum Cyanide

39. Establishing Stable Octets 2 Options 1. Transfer of electrons between atoms – Form Ionic Bonds 2. Sharing electrons between atoms

40. Obtaining a Stable Octet by Sharing Example: H (hydrogen) A gas at room temperature Has one valence Electron O (oxygen) A gas at room temperature A group 16 element Has 6 valence electrons Could they achieve a stable octet by transferring electrons? Could H give up its only electron and have a noble gas configuration? No electrons!

41. Sharing Electrons Between Atoms When atoms collide with enough energy to cause a reaction And neither atom attracts electrons strongly enough to take electrons from the other atom (small difference in electronegativity) The atoms combine by sharing valence electrons

42. Reaction of Hydrogen and Oxygen Hydrogen needs one more electron to have the same electron configuration as He Oxygen needs two more electrons to have the same electron configuration as Ne Hydrogen and Oxygen can share one electron from each atom. This makes Hydrogen stable But Oxygen still has only 7 valence electrons

43. Sharing to M ake Oxygen Stable Oxygen gets a complete octet by sharing an electron with another hydrogen This explains the formula of H2O

44. Electrons always rearrange in a chemical reaction

45. Covalent Bond The attraction of two atoms for a shared pair of electrons is called a covalent bond Notice, neither atom has an ionic charge A compound whose atoms are held together by covalent bonds is called a covalent compound A molecule is an uncharged group of two or more atoms held together by covalent bonds

46. Sharing More Than Two Electrons More than two electrons can be shared. The reaction Between Carbon and Oxygen for example You can arrange these 16 valence electrons to produce a molecule in which all three atoms have a noble gas configuration (a complete octet)

47. Sharing two pairs of Electrons: Double Covalent bonds are formed Atoms can also form Triple bonds

48. Molecular Elements Molecular Elements: a molecule that forms when atoms of the same element bond together They are not compounds (not two elements) 7 nonmetal elements naturally found as diatomic molecules: 1. Hydrogen 2. Nitrogen 3. Oxygen Gases 4. Fluorine 5. Chlorine 6. Bromine -liquid 7. Iodine- solid Allotropes: molecules of an element that form different crystalline structures. The properties of allotropes are usually different, because structure is important

49. Formulas and Names of Covalent Compounds Binary inorganic compounds (2 elements, not carbon) The Suffix –ide Write first nonmetal followed by the name of the second nonmetal with its ending changed to – ide The element closest to the left of the periodic table is written first ( some exceptions with H) If both are in the same group, name the one lower on the column 1 st. Indicating the number of atoms Add a prefix to the name of each element indicating the number of each element

50. Add prefix to indicate number of atoms If only one atom of the first element is listed, the mono is usually left out If adding the prefix creates double vowels, the first is usually omitted

51. Example of Naming Protocol FORMULASNAMES NONitrogen monoxide NO2Nitrogen dioxide N2ODinitrogen monoxide N2O5Dinitrogen pentoxide

52. Practice Naming Name the following compounds 1. CO2 2. NO2 3. SO3 4. PCl3 5. NO 6. P2O5

53. ANSWERS Name the following compounds 1. CO2 CARBON DIOXIDE 2. NO2 NITROGEN DIOXIDE 3. SO3 SULFUR TRIOXIDE 4. PCL3 PHOSPHORUS TRICHLORIDE 5. NO NITROGEN MONOXIDE 6. P2O5 DIPHOSPHORUS PENTOXIDE

54. General Atomic Bonding Trends Two nonmetallic elements usually achieve stability by sharing electrons to form a covalent compound Reacting atoms, when one is a metal and one a nonmetal, are much more likely to transfer electrons and form an ionic compound.

55. Comparing Ionic and Covalent bonds When elements combine they form either ions or molecules This changes them dramatically, this is why compounds have different properties from the elements that make them up

56. Properties of Ionic Compounds Composed of well-organized, tightly bound ions They form strong three-dimensional crystal structures They are crystalline solids at room temperature They are generally hard, rough and brittle They have high melting points They are generally soluble in water and form a solution which conducts electricity (called an electrolyte) In liquid state they also conduct electricity

57. Properties of Covalent Compounds Relatively weak Interparticle forces: forces between particles that make up a substance The molecules have no ionic charge so the attractive force between them is weak Many are liquid or gas at room temperature If they are solid at room temp, they have low melting point Ex. Sugar They do not conduct electricity Many do not dissolve in water (ex vegetable oil), but some do (sugar) Generally Less soluble in water

58. Interparticle Forces Make the Difference Interparticle Forces are the key to determining a substances state of matter at room temperature as well as many other properties

59. Compare and Contrast Properties Ionic Compounds Covalent Compounds 1. Ions held tightly in solid state by strong interparticular forces- solid at room temp 2. Good conductors in liquid form and when dissolved in water 3. Water soluble- ions are attracted by water 1. Much weaker interparticular forces hold them together more loosely- liquid or gas at room temp (few solids) 2. Not electrical conductors 3. Less soluble or insoluble in water-not attracted by water

60. Check your Understanding 1. Describe two processes by which elements can form stable compounds? What is the type of bonding that occurs from each process? 2. An unknown compound dissolves in water but does not conduct electricity. Is the compound more likely ionic or covalent? Explain 3. Why does NaCl have to be heated to 800 degreesC before melting, and candle wax starts to melt at 50 degrees C. 4. Explain why ionic compounds conduct an electric current in solution but covalent compounds do not?

61. Answers 1. Two processes by which elements can form stable compounds are transferring valence electrons (Ionic Bonds) or sharing valence electrons (Covalent Bonds) 2. It is more likely to be covalent because ionic compounds in solution would be made of mobile ions that would conduct an electrical current 3. NaCl is an ionic compound and is held together by strong interparticle forces which have to be broken in order to melt, candle wax is a covalent compound with very weak interparticle forces so melting is easy. 4. To conduct electricity there must be ions that are free to move so that they can pass the electrons along, this does not happen with covalent compounds but does with ionic compounds in solution.

62. Predicting the Type of Bond The type of bond formed depends on two properties 1. Electron configuration 2. Attraction for electrons: electronegativity In some covalent bonds the sharing is not even These bonds are called polar covalent bonds They have some ionic character The unequal sharing creates 2 poles (- end and + end) The less electronegative atom will be positive, less attraction for the electron Differences in electronegativity can determine bond type Differences greater than 2.0 makes ionic bond Differences between 0.8 and 2.0 makes polar covalent Differences between 0.0 and 0.5 covalent

63. Lets See how This Works! The bond between calcium and oxygen, is it ionic, covalent or polar covalent? Ca electonegtaivity is 1.0 O electonegtaivity is 3.5 3.5 - 1.0 = 2.5 2.5 is greater than 2.0 so it is an ionic bond!

64. Applying Our Knowledge Using figure 9.2 0n page 302, determine the electronegativity difference to classify the bonds between the following atoms as ionic, covalent or polar covalent. 1. NiO 2. BN 3. CaCl2 4. FeSi 5. NaF 6. Zn3P2

65. Answers 1. NiO Ni 1.8, O 3.5, 1.8 – 3.5 = 1.7 polar covalent 2. BN B 2.0, N 3.0, 2.0 – 3.0 = 1.0 polar covalent 3. CaCl2 Ca 1.0, Cl 3.0, 1.0 – 3.0 = 2.0 ionic 4. FeSi Fe 1.8, Si 1.8, 1.8 – 1.8 = 0.0 covalent 5. NaF Na 0.9, F 4.0, 4.0 – 0.9 = 3.1 ionic 6. Zn3P2 Zn 1.6, P 2.1, 1.6 – 2.1 = o.5, covalent

66. Bonding in Metals Bonding in metals DOES NOT RESULT IN COMPOUNDS It results in an interaction that holds metal atoms together and accounts for some of their common properties. Remember, metals are Malleable (thin sheets) and ductile (drawn into wires) and conduct electricity Conductivity is a measure of how easily electrons can flow through a material- electrical current. THESE PROPERTIES ARE THE RESULT OF THEIR BONDS

67. How Do They Bond? Metal to Metal bonding does not involve valence electron transfer, as it does in metal-nonmetal bonding Metal atoms release their valence electrons in a sea of electrons, shared by all of the metal atoms This is called a metallic bond Positively charged nucleus surrounded by loosely associated electrons shared with all surrounding nucleus

68. Properties Associated with Metallic Bond Electrons are bonded to a large network, not to a single atom. More freedom of movement Easily reorganize (bendable, stretchable etc.) Easy, free movement of electrons makes conductivity easy to understand

69. Comparing and Contrasting Ionic, Covalent and Metallic Bonds Ionic BondsCovalent Bonds Metallic Bonds ElectronsTransferredShared, evenly or unevenly Electron Sea BondMetal to NonmetalNonmetal to Nonmetal Metal to Metal Electronegativity Differences Differences greater than 2.0 Differences betwn 0.0 and 2.0 N/A Make CompoundsYes, by attraction of opposite charged ions Molecules, or molecular elements No Properties State (STP)Crystalline solidLiquid, gas, or solidMalleable and ductile solid Melting Pthighlow ConductivityLiquid and aqueous state, yes noyes Water solubility highlowno