CHEMICAL FORMULAS AND CHEMICAL COMPOUNDS Honors Chemistry 412 Chapter 7

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1 CHEMICAL FORMULAS AND CHEMICAL COMPOUNDS Honors Chemistry 412 Chapter 7 Nomenclature Systematic way of writin formulas and namin compounds. Purpose: Removes the need to memorize all the common names of compounds Formula Writin for Ionic Compounds Binary Ionic Compounds Ionic Bond between two atoms. Total chare of all compounds must equal zero! Total (+) = Total (-) Predictin Chares of the S and P block: What about the Transition Metals? No way to predict the chare of a transition metal from the periodic table, and many can have multiple chares For those that only have one chare: You ll be iven the chares. Ex: A 1+, Zn 2+ For those that can have multiple chares: Use the Stock System of Namin Roman numerals are used to indicate the positive chare of the metal ion Iron (III) = Fe 3+ Lead (IV) = Pb 4+ Criss-Cross Method Can be used with any type of ionic compound Identify the chares of both the + and ions. Use the PT or the reference sheet If the chares are equal, no subscripts needed (one to one ratio) If the chares are not equal, criss - cross the chares and write them without (+/-) sins as subscripts. Example: 2 Ba I 1- BaI 2 If the subscripts can be reduced, reduce to the lowest whole number ratio. 1

2 Practice Formulas Use the Criss Cross method to write the formula unit for the followin Binary Ionic Compounds: (Zn + O) Zn 2+ O 2- ZnO (Fe 3+ + Cl) (Ba + N) Fe 3+ Cl 1- FeCl 3 Ba 2+ N 3- Ba 3 N 2 Formula Writin for Ionic Compounds Ternary Ionic Compounds Ionic bond between an element and a polyatomic ion. Combinations of 2 or more non-metals that form common ions. Most are neatively chared except NH 4 1+ Must be placed in ( ) if more than 1 is needed. (Sn 4+ + S) Sn 4+ S 2- SnS 2 (Cu 1+ + P) Cu 1+ P 3- Cu 3 P Criss Cross Method w/polyatomics We can also use the Criss Cross method when we have a polyatomic ion involved: Na and PO 4 3- Na Na 3 PO PO4 More Practice with the Criss-Cross Method Write the formula unit for the followin Ternary Ionic Compounds: (Zn + OH - ) Zn(OH) 2 (Fe 3+ + ClO 3 1- ) Fe(ClO 3 ) 3 NH 4 1+ and CO NH 4 CO (NH 4 ) 2 CO 3 Use parentheses ONLY when you add a subscript to a polyatomic ion! You CANNOT combine the subscripts! (Ba + NO 3 1- ) (Sn 2+ + SO 3 2- ) (NH P) Ba(NO 3 ) 2 SnSO 3 (NH 4 ) 3 P Namin Ionic Compounds Rules: Write the name of the cation. If it is a stock metal, include the roman numeral! Write the name of the anion. If it is a sinle element, chane the endin to ide If it is a polyatomic, make NO chanes! Practice Namin Ionic Compounds 1. NaCl 1. Sodium Chloride 2. FeCl 2 2. Iron(II) Chloride 3. CaF 2 3. Calcium Fluoride Examples: Al 2 O 3 CuS MSO 4 Aluminum Oxide Copper (II) Sulfide Manesium Sulfate 4. KI 5. Ga 2 S 3 6. SnO 4. Potassium Iodide 5. Gallium Sulfide 6. Tin(II) Oxide 2

3 More Practice 1. Ca 3 (PO 4 ) 2 1. Calcium Phosphate 2. ANO 2 2. Silver Nitrite Writin Formulas from Names Identify the cation and the anion in the compound Identify their chares Criss Cross! (Reduce if necessary) 3. Zn(OH) 2 4. KC 2 H 3 O 2 3. Zinc Hydroxide 4. Potassium Acetate Ex: Tin (IV) Sulfate Sn 4+ So 4 2- Sn 2 (SO 4 ) 4 Sn(SO 4 ) 2 Practice Write formulas for the followin compounds: 1) Silver Sulfide 1) A 2 S 2) Manesium Nitrate 2) M(NO 3 ) 2 3) Copper(II) Nitride 3) Cu 3 N 2 4) Chromium(III) Sulfite 4) Cr 2 (SO 3 ) 3 Name the followin compounds: 1) K 2 SO 4 1) Potassium Sulfate 2) Fe(NO 3 ) 3 2) Iron(III) Nitrate 3) Ca 3 P 2 3) Calcium Phosphide 4) SnO 2 4) Tin(IV) Oxide Writin/Namin Covalent Compounds Rules: Write the name of the least electroneative element. If there are more than one atom of that element in the formula, attach the appropriate prefix: Write the name of the second element, chanin the endin to ide. Attach the appropriate prefix REGARDLESS of how many atoms there are in the formula! O s or A s at the end of the prefix may be dropped when the followin element name beins with a vowel Monoxide instead of monooxide Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10 Example P 4 O 10 Tetraphosphorus Decoxide # of P s # of O s -ide endin Determinin Formulas from Names for Covalent Compounds Use the prefixes to determine the subscripts: Carbon Tetraiodide CI 4 Try some: No prefix = 1 carbon Tetra = 4 iodines ICl 3 PBr 5 N 2 O 5 Iodine trichloride Phosphorus Pentabromide Dinitroen Pentoxide Dinitroen Trioxide Di = two nitroens Tri = three oxyens N 2 O 3 3

4 Write formulas for each: Binary Acids / Oxyacids Phosphorus Pentafluoride Carbon tetrachloride Carbon disulfide PF 5 CCl 4 CS 2 All acids contain the element H. H is always written 1 st in any formula representin acids. Binary Acids Contain Hydroen + a non-metal. Oxyacids Contain Hydroen + a polyatomic ion Binary Acids Binary Acids Namin: Must bein with the prefix Hydro- Must end in the suffix ic. Place the nonmetal between the prefix and suffix. Example HCl Hydrochloric Acid Writin Formulas: Always place the H first. Identify the nonmetal in the acid. Cross the chares on the H 1+ and the nonmetal as subscripts. Example Hydrosulfuric Acid H +1 S 2- H 2 S Binary Acids Practice Write the name for each of the followin acids: HI Hydroiodic acid H 2 S Hydrosulfuric acid H 3 N Hydronitric acid Write the formula for the followin acids: Hydrofluoric acid HF Hydrophosphoric acid H 3 P Hydroselenic acid H 2 Se Oxyacids Namin: Identify the polyatomic ion after the H. Write the name of the non-metal in the polyatomic ion. If the polyatomic ion ends in: -ate chane to ic -ite chane to ous Example H 2 SO 4 Sulfate Sulfuric Acid H 2 SO 3 Sulfite Sulfurous Acid 4

5 Oxyacids Writin: Identify the root of the polyatomic ion. If the acid ends in: -ic use the ate endin -ous use the ite endin Place the H in front of the polyatomic ion and cross the chares if needed. Example Phosphoric Acid Phosphoric = Phosphate (PO 4 ) 3- Oxyacids Practice Write the name for the followin acids: HNO 3 Nitric acid H 2 CO 3 Carbonic acid HC 2 H 3 O 2 Acetic acid Write the formula for the followin acids: Nitrous acid HNO 2 Perchloric acid HClO 4 Phosphorous acid H 3 PO 3 H 3 PO 4 Hydrates Ionic compounds that contain absorbed water. Water is NOT chemically bonded to the compound, but is essentially trapped with it in a definite ratio We indicate this by usin our usual prefixes on the word hydrate to tell how many water ecules to one formula unit of the compound Example: MSO 4 5H 2 O NOT a multiply symbol! Manesium Sulfate Pentahydrate Oxidation Numbers To show the eneral distribution of electrons amon the bonded atoms in a ecule or polyatomic ion, oxidation states are assined to the atoms in the compound or ion. Similar to ionic chares, but they don t have an exact physical meanin. Useful when explainin chemical reactions and balanced equations. Rules for Oxidation Numbers Note that all elements in the pure state have oxidation numbers equal to zero. Stock system over Prefix namin Instead of usin the prefixes mono to deca, the oxidation numbers can be used as Roman numerals like the stock namin system. Ex. SO 2 sulfur dioxide Sulfur (IV) Oxide SO 3 sulfur trioxide Sulfur (VI) Oxide 5

6 Identify the oxidation states of each element: HNO 3 KMnO 4 N 2 O 3 NaC 2 H 3 O 2 Chemical Measurements Atomic Mass The relative mass of a sinle atom. Measured in atomic mass units (amu) Relative scale based upon the mass of the carbon-12 isotope 1 amu the mass of one proton or neutron Found on the periodic table Formula Mass Sum of the atomic masses for each atom contained in a compound. Calculatin Formula Mass Determine the formula mass of sulfuric acid, H 2 SO 4. 2(1 amu) + 1(32 amu) +4(16 amu) 2 amu + 32 amu + 64 amu 98 amu The Mole The number of atoms of an element equal to the number of atoms in exactly 12.0 of carbon-12. Referred to as a countin number Dozen =? 12 The e is a specific number as well: 1 Mole = 6.02 x atoms Known as Avoadro s Number Molar Mass Mass in rams of 1 e of any substance. Equivalent to the formula mass of a compound and to the atomic mass of an element. 1 of S = 32 S (usually written 32/) 1 of H 2 SO 4 = 98 H 2 SO 4 Determinin Molar Mass Determine the formula mass and the ar mass of C 6 H 12 O 6. C: 6 x 12amu = 72amu H: 12 x 1amu = 12amu O: 6 x 16amu = 96amu + Formula mass = 180 amu Molar mass = 180 / **Mathematically, Formula mass and Molar mass are exactly the same the only difference is the unit!** 6

7 Usin the Mole as a Conversion Factor Once we know ar mass, we can use it to convert between mass and the number of es. How many es would be contained in 11.2 of NaCl? Molar mass 1(23) 1(35.5) NaCl 11.2NaCl NaCl 58.5 NaCl Other Types of Mole Conversions 1 = 6.02 x particles Use with atoms, ecules, or formula units 1 = 22.4 L of as at STP (Molar Volume) STP = Standard Temperature and Pressure 0 C and 1 atmosphere of pressure **The e is the central unit in convertin the amount of substances in chemistry.** Mole Conversions We can use the e unit as a steppin stone between other units: Percent Composition Volume (L) Molar Volume: 22.4L = 1 e Moles Particles: Atoms Molecules Formula Units Mass () Molar Mass: # (from PT) = 1 e Avoadro s #: 6.02x10 23 particles = 1 e The percent (by mass) of each element in a compound. total mass of ar mass of element x 100 % of that element compound Example: Determine the % composition of each element in H 2 O. 2 H : x % H 18 ar mass of H2O O : x % O 18 Practice % Composition Determine the % composition of each element in the followin compounds: 1. Na 2 SO 4 Na : 46 x 100 % 32.4% CaO 40 Ca: x 100 % 71.43% Al 2 (CO 3 ) 3 54 Al: 234 x 100 % 23.08% 32 S : 142 O : x 100 % 22.5% 64 O : x 100 % 45.1% x 100 % 28.57% C : x 100 % 15.38% 234 O : 144 x 100 % 61.54% 234 % Composition Usin Mass Data Determine the percent composition of a sample that has a total mass of 5.50, of which 3.30 is silver and 2.20 are sulfur A : x % A S : x % S

8 % Composition of Hydrates To determine the % of water: Add up the entire ar mass of the hydrate (includin water) Add up just the mass of the water Divide Determine the % of water in CaCO 3 10H 2 O. Ca : 1 x 40 = 40 C : 1 x 12 = 12 O : 3 x 16 = 48 H 2 O: 10 x 18= O : H x 100 % 64.29% 280 Usin Percent Composition Determine the portion of a sample that is a sinle element Determine the percentae composition of that element Use a ratio to determine the unknown mass Determine the mass of A in 120 of ACl. Molar mass: = 143.5/ 108 A : x % x x x Practice 1. Determine the mass of Ca found in 400 of CaCO x Ca : x % 100 x Determine the mass of K found in 50 of KClO 3 4H 2 O x K : x % x Determinin Chemical Formulas Empirical Formula (Simplest Formula) Smallest whole number ratio of atoms in a chemical formula. Found by comparin the number of es of each element If you are iven mass data, simply convert each mass value to es If you are iven percentaes, assume that you have a 100 ram sample. Then, use your percentaes as mass values and convert to es Find the Empirical formula for a compound that contains Na, S, and O. Na S O These will be the subscripts of your compound! Empirical Formula : Na 2 SO 4 To et the LOWEST whole number ratio, simply divide each number of es by the LEAST number of es Find the Empirical formula for a compound that contains 26.56% K, 35.41% Cr, 38.08% O. K Cr O Empirical Formula : K 2 Cr 2 O 7 Remember, assume that you have a 100 sample and use your percentaes as mass values! Divide by the least # of es Doesn t round up without chanin the ratio best to multiply to et a whole number ratio! 8

9 Try one on your own: Find the empirical formula for a compound which contains 6.5 K, 5.9 Cl and 8.0 O K Cl O Empirical Formula : KClO 3 Calculatin Molecular Formulas Molecular Formula Formula of a compound as it naturally occurs For an ionic compound: equivalent to the empirical formula For a covalent compound: a whole number multiple of the empirical formula To find Molecular Formula Compare the empirical ar mass to the ar mass iven to you in the problem to find the multiplier (X) Multiply the subscripts in your empirical formula by X to et the ecular formula Molecular ar mass X Empirical ar mass Determine the ecular formula of a compound havin an empirical formula of CH and a ecular mass of / Empirical ar mass 1(12) 1(1) 13 Molecular ar mass X Empirical ar mass X 13 X Molecular Formula = C 6 H 6 A compound with a ecular mass of 34 is found to consist of 0.44 H and 6.92 O. What is its ecular formula? Determine the empirical formula and its mass. Then, use them to find ecular formula: H O Molecular ar mass X Empirical ar mass X Empirical Formula: HO X 2 Empirical Molar Mass: 17 / Molecular Formula = H 2 O 2 The explosive, TNT, is composed of 39.4% C, 2.4% H, 13.1% N and 45.1% O. a) Determine the empirical formula for TNT. b) The ar mass for TNT is 213 /. What is the ecular formula for TNT? C H N O Empirical Formula = C 7 H 5 N 2 O 6 Empirical Molar Mass = 213 / 213 X 213 X 1 Molecular Formula Ribose is an important suar that is found in DNA and RNA. Ribose has a ar mass of 150 / and a chemical composition of 40.0 % Carbon, 6.67 % hydroen and 53.3 % oxyen. What is the ecular formula for ribose? Empirical formula: CH 2 O Empirical Molar Mass: 30/ To find ecular formula: 150 X X 5 30 Molecular Formula = C 5 H 10 O 5 9