Chemical Formulas and Chemical Compounds Heart cell rhythm depends on the opening and closing of a complex series of valves on the cell membrane, called ion channels. Some valves let certain ions ike potassium (K+) flow out, others let different ions like sodium (Na+) flow in. There are also pumps that actively move ions one direction or another. Notes 7 Ions • Cation: A positive ion • Mg2+, NH4+ • Anion: A negative ion • Cl-, SO42- • Ionic Bonding: Force of attraction between oppositely charged ions. Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Predicting Ionic Charges B3+ Al3+ Ga3+ Group 13: Loses 3 electrons to form 3+ ions Predicting Ionic Charges Neither! Group 14 elements rarely form ions. Group 14: Lose 4 electrons or gain 4 electrons? Predicting Ionic Charges N3- Nitride P3- Phosphide As3- Arsenide Group 15: Gains 3 electrons to form 3- ions Predicting Ionic Charges O2- Oxide S2- Sulfide Se2- Selenide Group 16: Gains 2 electrons to form 2- ions Predicting Ionic Charges F1- Fluoride Br1- Bromide Cl1-Chloride I1- Iodide Group 17: Gains 1 electron to form 1- ions Predicting Ionic Charges Group 18: Stable Noble gases do not form ions! Predicting Ionic Charges Groups 3 - 12: Many transition elements have more than one possible oxidation state. Iron(II) = Fe2+ Iron(III) = Fe3+ Predicting Ionic Charges Groups 3 - 12: Some transition elements have only one possible oxidation state. Zinc = Zn2+ Silver = Ag+ Binary Ionic Compounds • Binary ionic compounds means two ions, • one that is positive in charge (cation) • one that is negative in charge (anion) • that react to form a compound. Naming Ionic Binary Compounds 1. The ion with the positive charge (cation) is always written before the ion with the negative charge (anion) 2. The first word is the name of the element of which the cation originally came. (Example: Na+ would be called Sodium) 3. The last word is the name of the element of which the anion originally came. (Example: Clwould become chlorine, but the first part of the word is used and -ide is added to the end, so the last word would be Chloride.) 4. Put the two words together and that is the name of the compound. (Example: Na+ and Clwould become Sodium Chloride.) Naming Ionic Compounds • 1. Cation first, then anion • 2. Monatomic cation = name of the element • Ca2+ = calcium ion • 3. Monatomic anion = root + -ide • Cl- = chloride • CaCl2 = calcium chloride Naming Ionic Compounds (continued) Metals with multiple oxidation states some metal forms more than one cation • - use Roman numeral in name • - • PbCl2 • Pb2+ is cation • PbCl2 = lead(II) chloride Polyatomic Ions • Polyatomic Ions are ions that contain a number of ions. • There is no way to learn how to write their names, except to commit them to memory Ion NH4+ NO2- Common Polyatomic Ions (VIP) Name Ion Name Ammonium O2-2 Peroxide Nitrite CrO4-2 Chromate NO3SO3-2 SO4-2 Nitrate Sulfite Sulfate Cr2O7-2 MnO4C2H3O2- Dichromate Permanganate Acetate HSO4OHCNPO4-3 Hydrogen Sulfate Hydroxide Cyanide Phosphate ClO4ClO3ClO2ClO- Perchlorate Chlorate Chlorite Hypochlorite HCO3CO3-2 Hydrogen Carbonate Carbonate HPO4- Hydrogen Phosphate H2PO4- Dihydrogen Phosphate Writing Ionic Compound Formulas Example: Ammonium sulfate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. ( NH4+) SO42- 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. 2 Not balanced! Writing Ionic Compound Formulas Example: Iron(III) chloride 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Fe3+ Cl- 3 Not balanced! Writing Ionic Compound Formulas Example: Aluminum sulfide 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. 3+ Al 2 2S 3 Not balanced! Writing Ionic Compound Formulas Example: Magnesium carbonate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. Mg2+ CO32They are balanced! Writing Ionic Compound Formulas Example: Zinc hydroxide 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 2+ Zn 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ( OH- )2 Not balanced! Writing Ionic Compound Formulas Example: Barium nitrate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 2+ ( Ba NO3 ) 2 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Not balanced! Writing Ionic Compound Formulas Example: Aluminum phosphate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3+ Al PO4 3- They ARE balanced! Binary Covalent Compounds • Binary covalent compounds are those that do not involve metals or ions. • An example of the difference between a covalent compound is that CO2 is a covalent compound, but NaCl is not, because it contains Na+, a metal and an ion.) Naming Binary Compounds • - • • • • - Compounds between two nonmetals First element in the formula is named first. Second element is named as if it were an anion. Use prefixes Only use mono on second element P2O5 CO2 CO N2O = diphosphorus pentoxide = carbon dioxide = carbon monoxide = dinitrogen monoxide Rules for naming a binary covalent compound 1. The first element in the formula uses the whole name of the element, much like binary ionic compounds. (Example: In NO, the first word would be Nitrogen.) 2. The second element in the formula only uses the first half of the word and -ide is added in place of the removed ending, much like binary ionic compounds. (Example: In NO, the first part of the second word would be oxide.) 3. So the person reading the name can determine what the subscript is on each element, a prefix is added to show how many of each element are used. The first word of the formula does not use momo, so CO (Carbon Monoxide), NOT (Monocarbon Monoxide). Prefixes in Chemical Names mono 1 di tri tetra penta 2 3 4 5 hexa hepta octa 6 7 8 nona 9 deca 10 Calculating Formula Mass Calculate the formula mass of magnesium carbonate, MgCO3. 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g Calculating Percentage Composition Calculate the percentage composition of magnesium carbonate, MgCO3. From previous slide: 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g 24.31 Mg 100 28.83% 84.32 12.01 C 100 14.24% 84.32 48.00 O 100 56.93% 84.32 100.00 Formulas Empirical formula: the lowest whole number ratio of atoms in a compound. Molecular formula: the true number of atoms of each element in the formula of a compound. molecular formula = (empirical formula)n [n = integer] molecular formula = C6H6 = (CH)6 empirical formula = CH Formulas (continued) Formulas for ionic compounds are ALWAYS empirical (lowest whole number ratio). Examples: NaCl MgCl2 Al2(SO4)3 K2CO3 Formulas (continued) Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio). Molecular: H2O C6H12O6 C12H22O11 Empirical: H2O CH2O C12H22O11 Empirical Formula Determination 1. Base calculation on 100 grams of compound. 2. Determine moles of each element in 100 grams of compound. 3. Divide each value of moles by the smallest of the values. 4. Multiply each number by an integer to obtain all whole numbers. Empirical Formula Determination Adipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula of adipic acid? 49.32 g C 1 mol C 4.107 mol C 12.01 g C 6.85g H 1 mol H 6.78 mol H 1.01 g H 43.84 g O 1 mol O 2.74 mol O 16.00 g O Empirical Formula Determination (part 2) Divide each value of moles by the smallest of the values. 4.107 mol C Carbon: 1.50 2.74 mol O 6.78 mol H Hydrogen: 2.47 2.74 mol O 2.74 mol O Oxygen: 1.00 2.74 mol O Empirical Formula Determination (part 3) Multiply each number by an integer to obtain all whole numbers. Carbon: 1.50 x 2 3 Hydrogen: 2.50 x 2 5 Oxygen: 1.00 x 2 2 Empirical formula: C3H5O2 Finding the Molecular Formula The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid? 1. Find the formula mass of C3H5O2 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g Finding the Molecular Formula The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid? 2. Divide the molecular mass by the mass given by the emipirical formula. 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g 146 2 73 Finding the Molecular Formula The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid? 3. Multiply the empirical formula by this number to get the molecular formula. 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g 146 2 73 (C3H5O2) x 2 = C6H10O4 The Mole 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023 There are exactly 12 grams of carbon-12 in one mole of carbon-12. Avogadro’s Number 6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro (1776-1855). I didn’t discover it. Its just named after me! Amadeo Avogadro Calculations with Moles: Converting moles to grams How many grams of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.94 g Li 1 mol Li = 24.3 g Li Calculations with Moles: Converting grams to moles How many moles of lithium are in 18.2 grams of lithium? 18.2 g Li 1 mol Li 6.94 g Li = 2.62 mol Li Calculations with Moles: Using Avogadro’s Number How many atoms of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.02 x 1023 atoms Li 1 mol Li = 2.11 x 1024 atoms Li Calculations with Moles: Using Avogadro’s Number How many atoms of lithium are in 18.2 g of lithium? 18.2 g Li 1 mol Li 6.94 g Li 6.02 x 1023 atoms Li 1 mol Li (18.2)(6.02 x 1023)/6.94 = 1.58 x 1024 atoms Li