Chapter 7, Sections 1-2

Transcription

1 Chapter 7, Sections 1-2 Chemical Formulas & Compounds Nomenclature and Oxidation numbers C. Goodman, Doral Preparatory Academy, Based on a PowerPoint by Mrs. S. Temple,

2 Essential Questions Section 1 1. Binary ionic compounds How can you determine their names and chemical formulas? 2. Binary molecular compounds How can you determine their names and chemical formulas?

3 Vocabulary Section 1 1. Acid 2. Binary ionic compounds 3. Formula unit 5. Monatomic ion 6. Polyatomic ion 7. Subscript 4. Chemical formula

4 Chemical Formula Relative # of atoms of each kind in a. Molecules: a single molecule b. Ionic compound: formula unit Examples How many atoms are in each compound? CH 4 (methane) Pb(NO 3 ) 4 (lead (IV) nitrate)

5 Nomenclature: Ionic compounds I: Ions 1. Cations Element s name Al 3+ is Aluminum 2. Anions Drop ending of elements name, add ide Cl - is chloride

6 Formation of Cations Cation s charge = +(number of valence electrons lost during ion formation) Also: Cadmium Cd 2+ Gallium Ga 2+ Zinc Zn 2+ Silver Ag +

7 Formation of Anions Anion s charge = -(#electrons gained during ion formation)

8 Practice naming anions! Element symbol & name Name of anion N nitrogen Nitride 3- S sulfur Se Selenium O oxygen P phosphorus Cl chlorine F fluorine H hydrogen Br bromine I iodine Charge

9 Naming Ionic Compounds II: Binary Ionic compounds 2 elements + and charges must balance (= 0) Smallest possible whole number ratio

10 Nomenclature: Type I Binary Ionic Compounds 1. Write the name of the cation 2. Append the name of the anion Example: Al 2 O 3 Aluminum Aluminum oxide The cations of Type I compounds are those with reliable charges.

11 Predicting the formula of an ionic compound using the Criss-cross method Example: Aluminum and oxygen 1. Put the ions next to each other, cation first 2. Criss-cross charges to subscripts 3. You re done! Al 3+ O 2- Notes: a. If need be, reduce the subscripts to the lowest whole number ratio. b. Do not write 1 as a subscript it is understood Al 2 O 3

12 Practice! Cation Anion Formula Name Na + O 2- Na 2 O Sodium oxide Al S Mg Cl Lithium chloride Sr O Hydrogen sulfide K F Aluminum bromide

13 More Practice! Cation Anion Formula Name Strontium nitride Rb P Barium sulfide Cd P Hydrogen phosphide Zn N

14 Problem! This is easy when you re working with the reliable cations, which we learned above. BUT Most metals can have varying charges What happens when you have a compound with one of these metals? Introducing the STOCK SYSTEM!!! (pause for applause)

15 Nomenclature: Stock System (Type II compounds) Roman numeral after cation s name indicates charge of cation Example: Copper (III) chloride Cu 3+ Example: Iron (II) oxide Fe 2+ The cations of Type II compounds are those with variable charges.

16 Nomenclature of ionic compounds using the Stock system Example: Cu 3+ & Oxygen 1. Write name of cation & parentheses 2. Cation s charge in parentheses (Roman Numerals) 3. Name of anion Copper ( ) Copper (III) Copper (III) oxide

17 Practice! Cation Anion Formula Name Example Cu + O 2- Cu 2 O Copper (I) oxide Fe 3+ S 2- Iron (III) sulfide Cu 2+ Cl - Hg 2+ O 2- Sn 4+ S 2- V 3+ Br - Tin (II) fluoride Vanadium(III) iodide

18 Stock system continued Getting the name from a formula unit Problem: when I look at the formula unit, how do I determine the cation s charge? Example: Cu 2 O Reverse Criss-cross!!!

19 Reverse criss-cross Example: Cu 2 O 3 1. Give the anion its normal charge. 2. Reverse criss-cross to get the charge of the cation. Keep the subscripts as well. 3. BUT you re not done until you 4. Check charges to make sure that they balance: multiply subscript x superscript Cu 2 3+ O 3 2- Cu 3+ = Copper (III) Copper (I) oxide Cu 2 3+ O x 2 x You re cool!

20 What if the charges don t balance? Sn S 2 Example: SnS 2 1. Adjust the cation s charge 2. Stock system nomenclature 3. You re done! x 1 x Sn S 2 Tin (IV) sulfide

21 Name Practice Time! Cation charge Anion charge Formula unit Example Copper (III) phosphide Cu 3+ P 2- Cu 2 P 3 Iron(III) sulfide Tin (IV) phosphide Mercury(I) bromide FeCl 3 HgFl 2 CuO 2

22 More Practice! Formula Crisscross Cation s charge Name Example VS 2 Sn 4+ Tin(IV) sulfide VS 2 2- CoI 2 HgI 2 PbS 2 Copper (II) bromide Iron (II) sulfide Copper (II) oxide Cobalt (III) fluoride

23 Stock system continued Determining the formula unit starting from the name 1. Write the ions, cation first 2. Criss-cross 3. Check charges to make sure they balance 4. Write formula unit Example: Copper (II) chloride Cu 2+ Cl - Cu 1 2+ Cl 2 - Cu 1 2+ Cl x 1 x CuCl 2

24 Polyatomic Ions A charged group of COVALENTLY bonded atoms

25 Understanding Formulas for Polyatomic Ionic Compounds

26 Polyatomic ions: Oxyions Polyatomic ions that contain oxygen, Example: hydroxide OH - Usually more than 1 type of each Example: BrO 3- (bromate), and BrO - hypobromite PLEASE NOTE You must memorize all of the Polyatomic Ions on Page 226 in your Chemistry Book!

27 Naming Oxyanions If it contains O or O 2 = (hypo) ite O 3 or O 4 =(per) ate or O 4 = per ate The prefixes and suffixes depend on the number of oxygens in the ion. e.g. ClO - hypochlorite NO 2 - nitrite e.g. NO 3 - nitrate ClO 4 - perchlorate

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29 Determining formula units for compounds containing oxyanions, using the Criss-cross method 1. Put the ions next to each other 2. Criss-cross 3. Check charges Example: Lead (IV) sulfate 4. If need be, reduce the subscripts to the lowest whole number ratio. Pb 4+ (SO 4 ) 2- Pb 4+ (SO 4 ) x 2 x Pb 2 (SO 4 ) 4 Pb(SO 4 ) 2

30 Practice! Name Cations Anion Formula unit Example Titanium (IV) cyanide Ti 4+ (CN) - Ti(CN) 4 Iron(III) sulfide Tin(IV) phosphate SnS 2 2- Mercury(II) cyanide Fe 2 (CrO 4 ) 3 Sn(ClO 4 ) 4 Hg(NO 2 ) 2 Co(OH) 3

31 Most common acids hydrogen + halogen Memorize: Hydrochloric acid HCl Hydrofluoric acid HF Oxyacids: hydrogen + oxyanion Memorize Phosphoric acid H3PO4 Nitrous acid HNO2 Nitric acid HNO3 Sulfurous acid H2SO3 Sulfuric acid H2SO4 Acetic acid CH3COOH Perchloric acid HCl)4, Carbonic acid H2CO3 Common Binary Acids See textbook p. 230

32 Naming Binary Molecular Compounds Prefixes a) Use with binary molecular compounds b) memorize these prefixes 1-10

33 Let s try a few! Molecular Formula Example: Mo 2 O 3 Name Molybdenum trioxide CCl 4 PCl 5 Selenium hexafluoride Diarsenic pentaoxide

34 Essential Questions Section What are oxidation numbers? 2. How are oxidation numbers assigned?

35 Vocabulary Section 2 1. Oxidation number 2. Oxidized 3. Reduced

36 Hold the phone! Why do I have to learn oxidation numbers? Oxidation numbers are helpful in chemistry. They are helpful in naming binary molecular compounds writing balanced equations and writing formulas. predicting what compounds can be made out of two or more elements.

37 Hold the phone #2 How are oxidation numbers different from ionic charges? Thank you for asking that question! Oxidation numbers are related to electronegativity, how tightly elements hold their electrons. Unlike charges, oxidation numbers apply to nonmetals. Nonmetals can have multiple oxidation numbers.

38 Two vocabulary words Oxidized an atom is oxidized when other elements have pulled the electrons away from it Reduced an atom is reduced when it pulls the electrons closer to it

39 Why oxidation numbers? Oxidation numbers are assigned in order to indicate the distribution of electrons among bonded atoms in compounds or polyatomic ions.

40 Assigning Oxidation Numbers Q: Why do I need to assign them? A: Many elements can have more than one oxidation state Note: the graphic below does not show all possible oxidation numbers for elements in groups

41 Assigning Oxidation Numbers Just follow some simple guidelines. and it s purrrr-tty easy to do.

42 Assigning Oxidation Numbers Step #1 Make an algebraic statement Step #2 Assign known oxidation numbers first Step #3 Solve for the unknown oxidation number(s)

43 Step 1 Algebraic Statement The sum of all oxidation numbers in a compound equals 0 for anything with a neutral charge e.g. elements and molecules OR Ionic charge for ions Assigning oxidation numbers

44 Step by Step 1. Make an algebraic sum 2. Assign known oxidation numbers 3. Solve for the unknown oxidation number 4. Put oxidation numbers in order of appearance Practice Problem #1: Assign oxidation #s for the elements in the compound NaCl. Application 1. Sum {Na} + {Cl} = 0 2. Known Na s oxidation number is Solve +1 + {Cl} = 0 {Cl} = Answer +1, -1

45 Step 2, continued Assign Knowns, solve for the unknown Assign known oxidation numbers first, and then solve for what s left. Assign knowns in order of precedence. As in school, there is a pecking order Assigning oxidation numbers

46 Step 2, continued Assign Knowns, solve for the unknown I. The senior class These elements always have the same oxidation numbers, so assign them first: a. Group 1 = +1 (with the exception of H) b. Group 2 = +2 c. Fluorine = -1 Assigning oxidation numbers

47 I. The senior class Examples: Determine the oxidation numbers for the elements in the following compounds: a. KI b. Li 2 S c. SF 4 d. Na 4 O Step 2, continued Assign Knowns, solve for the unknown Assigning oxidation numbers

48 Step 2, continued Assign Knowns, solve for the unknown I. The junior class These elements almost always have the same oxidation numbers, unless this would contradict the senior class rules, so assign them second: a. H = +1 UNLESS it is paired with an element whose electronegativity is <2.1 b. Oxygen = -2 UNLESS it is paired with a senior Assigning oxidation numbers

49 Step 3 Solve for the unknown I. The junior class Examples: a. CO 2 b. ClO - 3 c. H 2 SO 4 d. NiH e. OF 2 Assigning oxidation numbers

50 Step 2, continued Assign Knowns I. The sophomore class If senior and junior rules don t apply, assign oxidation numbers according to electronegativity 1. The element with the highest electronegativity gets an oxidation number equivalent to its charge. 2. If the electronegativities of the two elements are the same, assign oxidation numbers to those who have definite ionic charges first. Assigning oxidation numbers

51 Step 3 Solve for the unknown I. The sophomore class Examples: a. CS 2 b. ICl 3 c. AlBr 3 d. GeS 2 Assigning oxidation numbers

52 Step 2, continued Assign Knowns, solve for the unknown I. What about the freshman class??? The freshman class consists of all of the other elements. They have to fit in with all of the other rules. Assigning oxidation numbers

53 Assigning Oxidation Numbers SEE HANDOUT!! Let s try some together