Chemical Formula. ionic compounds form lattices. ionic compounds electrically neutral NO 2. geometric arrangement of ions.

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1 hemical Formula inventory of all atoms in a compound element symbol for nitrogen NO 2 element symbol for oxygen number nitrogen atoms = 1 number oxygen atoms = 2 element more to left on PT is written first ionic compounds form lattices geometric arrangement of ions no definite size 1.8 nm 1.0 mm 2.0 cm sodium chloride = Nal ionic compounds electrically neutral charge positive ions = charge negative ions Nal = 1 Na + and 1 l Li 2 S = 2 Li + and 1 S af 2 = 1 a 2+ and 2 F

2 Formula Unit hemical formula of ionic compound called Formula Unit smallest whole number ratio of ions that will be electrically neutral SrO = 1 Sr 2+ and 1 O 2- al 2 = 1 a 2+ and 2 l - Li 2 O = 2 Li + and 1 O 2- Na 64 l 64 Nal = 1 Na + and 1 l - 64 Na + and 64 l - Na l Na + and l Na + and l Na l smallest whole number ratio is same for different size lattices crossing over rule What is the formula unit of calcium nitride? a a 2+ N N why? periodic table total + charge 3 2 = 3 x 2 = = 2 total - charge 2 x 3 periodic table b/c ionic compounds electrically neutral a 3 N 2 crossing over rule What is the formula unit of magnesium oxide? periodic Mg Mg 2+ O 2- periodic O table why not Mg 2 O 2? 2 2 MgO table b/c the formula unit has smallest whole number ratio of ions that will be electrically neutral (1 to 1 smaller 2 to 2) 2

3 N 4 + N - polyatomic ions PO 4 SO 4 2- O 3 - g 2 2+ O - groups of atoms bonded together that have a charge O O + e O - atoms O O O -1 acts as a single ion O 3 - N 4 + polyatomic ions form ionic compounds O - 3 SO 4 N - g 2+ PO 4 2 O - 2- positive polyatomic ions can substitute a metal ion negative polyatomic ions can substitute a non-metal ion memorize this chart crossing over rule (polyatomic ions) What is the formula unit of calcium phosphate? periodic table a a 2+ ( PO 4 ) why use 3 2 table of polyatomic ions phosphate ( )? a 3 (PO 4 ) 2 (not phosphide) a 2+ a 2+ a 2+ PO 4 PO 4 2 PO 4 ions not PO 42 3

4 counting atoms in chemical formula a 3 (PO 4 ) 2 a 2+ a 2+ a 2+ # a 2+ ions = 3 # PO 4 ions = 2 PO 4 PO 4 1 P + 4 O 1 P + 4 O total = 2 P and 8 O 2 a naming ionic compounds (with polyatomic ions) metal name anion name for polyatomic ions substitute either part with name Table 3.5 Na 2 3 O 2 sodium acetate Li 2 r 2 O 7 lithium dichromate (N 4 ) 2 SO 4 ammonium sulfate naming ionic compounds (with ions not from main group) metal name anion name metal ions that can have different charges use roman numerals remember formula unit must have zero overall charge Fel 3 (Fe 3+ and 3l - ) iron (III) chloride or 2 O 7 (o 2+ and r 2 O 7 2- ) cobalt (II) dichromate 4

5 molecular compounds form molecules molecules are individual particles with definite size chemical formula does not have smallest whole number ratios NO 2 N 2 O 4 N and O = non-metals form molecular compounds different compounds both are molecules naming binary molecular compounds element further to left on PT first if in same group lower element comes first both elements get prefixes (mono, di, tri, tetra, penta, hexa, hepta, octa, nona; mono optional) second element gets ending -ide NO (2 elements) nitrogen oxide N 2 O dinitrogen oxide NO 2 nitrogen dioxide N 2 O 4 dinitrogen tetroxide Acids + + anion + - anion ydrogen acts as a non-metal Strong acids l NO 3 2 SO 4 + l - + NO SO 2-4 hydrochloric acid nitric acid sulfuric acid Weak acids 2 3 O 2 F O F - acetic acid hydrofluoric acid Acids are molecular compound because they can dissolve without dissociating into ions Ionic compounds must separate into ions to dissolve Weak acids have a small percentage of molecules separated into + and an anion, the rest stay together as one particle F ~ 95% + and F - 5% Strong acids separate 100% into + and anion in water l ~ 0 % + and l - ~ 100% 5

6 molecular compounds ionic compounds all other molecular compounds F ~ 95% (molecules) Acids are molecular compounds dissolve dissolve acids l + + l - ~ 100% dissolve + + F - ~5% separated ions (separated ions) Dissolved molecules cations (+ ions) anions (- ions) electrolytes ionic compounds and strong acids are called strong electrolytes - form ions in water - ions = conduct electricity + cation - anion weak acids = weak electrolytes - small % molecules ions - conduct electricity poorly molecular compounds = non-electrolytes water is a molecular compound and a non-electrolyte (remember is an exception it acts like a non-metal) tap water only conducts b/c ions are dissolved in it view quicktime movies on 1) electrolytes 2) aqueous acids 6

7 molecular vs ionic compounds chemical formula of ionic compound called formula unit has smallest whole number ratio of ions formula unit predicted from crossing over rule for each combination of ions there is only one formula unit in contrast different molecular compounds with same elements are numerous, NO, NO 2, N 2 O, N 2 O 4 etc. chemical formulas of molecular compounds predicted by Lewis Structures ( chapter 9) 7

8 mole concept for compounds as a counting unit the mole is also applied to molecules, ions, and formula units 1 al 2 formula unit a 2+ 1 mole al 2 formula units 1 mole NO 2 molecules l - l x al 2 formula units 6.02 x NO 2 molecules 8

9 counting moles ions in formula unit 1 mole al 2 = 6.02 x al 2 formula units ow many moles of a 2+ ions are present? 1 mole a 2+ ow many moles of l - ions are present? 2 moles l - why? a 2+ l - l - 4 wheels per 1 car 4 dozen wheels per 1 dozen cars 2 l - ions per al 2 formula unit 2 moles l - ions per mole al 2 formula units formula (aka molar ) of a compound sum of all elements molar/atomic es can be interpreted in amu per formula unit or grams per mole of formula units what is the formula of al 2? a 1 x l + 2 x amu atom amu formula unit or grams mole atom or grams al 2 mole al 2 molar (of a compound) is also a conversion factor Example. onvert moles of NO 2 into of NO 2 NO 2 N 1 x g/mol O 2 x g/mol moles multiply molar g/mol g NO moles NO 2 molecules x 2 1 mole NO = g NO 2 2 old unit conversion factor new unit moles molar grams 9

10 molar (of a compound) is also a conversion factor Example. onvert 6.66 grams of glucose 6 12 O 6 into moles of glucose 6 12 O 6 6 x x O 6 x g/mol divide molar moles 6.66 grams 6 12 O 6 x 1 mole 6 12 O 6 = 3.70 x 10-2 moles grams 6 12 O O 6 molecules old unit grams conversion factor 1 / molar new unit moles compound multiply molar divide molar moles of formula units, molecules, atoms, or ions divide Avogadro's number multiply Avogadro's number number formula units, molecules, atoms, or ions 3 different units to describe amounts of a compound like length of an object measure in mm, cm, inches, etc. percent composition from formula 1 formula unit of al amu a 2+ l - l amu amu l - a 2+ formula = amu % by l = 2 x amu x 100% amu = % l 2 l - l - l - x 100% a al 2+ 2 formula unit l - l amu sample al 2 2 x amu l - l - a amu l - 10

11 compound multiply molar divide molar moles of formula units, molecules, atoms, or ions divide Avogadro's number multiply Avogadro's number number formula units, molecules, atoms, or ions 11

12 F F moles of atoms vs molecules 2 fluorine atoms 1 fluorine molecule ow many moles of fluorine molecules (F 2 ) are in 5.1 grams of molecular fluorine? 5.1 grams fluorine molecules 1 mole F 2 molecules 38 grams F 2 molecules = 0.13 moles F 2 molecules ow many moles of fluorine atoms are in 5.1 grams of molecular fluorine? 5.1 grams fluorine atoms 1 mole F atoms = 0.26 moles F atoms 19 grams F atoms or = 0.13 moles F 2 molecules 2 mole F atoms 1 mole F 2 molecules F F if every molecule decomposed into atoms double 2 = 0.26 moles F atoms compound multiply molar divide molar moles of formula units, molecules, atoms, or ions divide Avogadro's number multiply Avogadro's number number formula units, molecules, atoms, or ions 12

13 chemical equations reactants 22.4 g Mg +? g O g MgO if 22.4 g Mg reacts with 16 g O, 38.4 g MgO form no Mg or O remain (apply conservation of ) 22.4 g Mg + 16 g O g MgO a balanced chemical equation! (aka chemical reaction) conversion factors ( reactants = products) ratios MgO products balance equation and their one overs 16 g O 2 16 g O g MgO 38.4 g MgO 22.4 g Mg 22.4 g Mg 38.4 g MgO 22.4 g Mg 22.4 g Mg 16 g O 2 16 g O g MgO 13

14 ratios as conversion factors What of MgO will form if 5.0 grams of Mg reacts with O 2? The balanced reaction is, 22.4 g Mg + 16 g O g MgO 5.0 g Mg x 38.4 g MgO 22.4 g Mg = 5.0 x = 8.57 g MgO hemical reactions (mole interpretation) MgO 22.4 g Mg g O g MgO convert all es to moles divide molar moles 1 mole Mg + ½ mole O 2 1 mole MgO mole ratios (conversion factors) also a balanced chemical equation! ½ mole O 2 ½ mole O 2 1 mole MgO 1 mole MgO 1 mole Mg 1 mole Mg 1 mole MgO 1 mole Mg 1 mole Mg ½ mole O 2 ½ mole O 2 1 mole MgO notation in chemical reactions (mole interpretation) Na 2 O 3 (s) + 2 l (aq) O 2 (g) + 2 O (l) +2 Nal (aq reactants products state of matter abbreviated in ( ) s = solid l = liquid g = gas aq = dissolved in water 2l mean 2 moles of l not same as 2 l 2 or l 2 or 2 l 2l = l numbers in front of compounds are called the stoichiometric numbers l 14

15 balancing a chemical reaction (mole interpretation) Fel 3 (aq) + NaO Fe(O) 3 (s) + Nal (aq) g/mol or grams per 1 mole g/mol or grams per 1 mole g/mol or grams per 1 mole grams not balanced! by inspection 1 O on left 3 on right now 3 Na on left 1 on right grams g/mol or grams per 1 mole Fel 3 (aq) + NaO Fe(O) 3 (s) + 3 Nal (aq) g 3 x g g 3 x g grams = grams balanced! balance this! Fe 3 O 4 + O Fe + O 2 3 Fe on left 1 on right so try Fe 3 O 4 + O 3Fe + O 2 and Fe are balanced but O is not if we change the stoichiometric numbers anywhere to balance O then Fe and will become unbalanced Fe 3 O O 3Fe + O 2 Now O is balanced but is not! there are special methods for balancing some types of reactions combustion reactions compound ( O) + O 2 (g) O 2 (g) + 2 O (l) You must remember this Example: Write the balanced combustion reaction of ethanol, 2 6 O. 2 6 O (l) + 3 O 2 (g) 2 O 2 (g) O (l) 1 moles O need 6 moles O 3 moles O 2 has 6 mole O!! 4 moles O + 3 moles O 7 moles O notice all the on right is in O 2 so if we do not change 2 6 O 2 will balance notice all the on right is in 2 O so if we do not change 2 6 O 3 will balance to write a standard combustion reaction You must remember this do not change the stoichiometric number of the compound 15

16 Empirical Formula experimentally determined chemical formula has smallest whole number ratio if atoms -for ionic compounds this is the formula unit -for molecular compounds this is not the chemical formula NO 2 nitrogen dioxide Examples: N 2 O 4 dinitrogen tetroxide 2 2 acetylene 6 6 benzene NO 2 and N 2 O 4 have different chemical formula but same empirical formula NO (acetylene )and 6 6 (benzene) different chemical formulas same empirical formula empirical formula chemical formula ethane = 2 6 empirical formula is the chemical formula with the smallest whole number ratio of the elements as they are in the compound empirical formula determined experimentally by decomposing a compound mole ratio of elements in ethane divide all subscripts by the smallest one empirical formula 1 3 or 3 of ethane converted to smallest whole number ratio 50.0 g ethane 40.0 g 10.0 g convert to moles 3.33 moles 10.0 moles there is no way to determine how many of each atom were in the molecule from decomposing and measuring es all we can do is measure the ratio of atoms chemical formulas conversion factors O O chemical equation for decomposition of O 2 into its elements/atoms written in moles description 44.0 grams O 2 ( 1 mole O 2 ) g O g g O O 2 ratios = conversion factors same equation re-written in g g O g g O g O g O g atoms O O grams O atoms / O ratio % O in O 2 % in O 2 ( 1 mole ) ( 2 mole O) 16

17 chemical formulas conversion factors 44.0 grams O 2 O 2 % in O g atoms O O grams O atoms g O 2 g x = g g O2 2 % in O 2 converts of O 2 into of empirical formula chemical formula expressed with smallest whole number ratio of atoms compound O done experimentally calculated divide by atomic O 2 O moles moles O moles element divide by atomic moles of element 1) chemical formula with ratios of moles 2) convert smallest whole number ratios 3) round to integers O O 1 6 O 2 divide all by smallest compound O O 2 O alculated divide by molar moles moles O moles O O O 17

18 ombustion analysis compound O compound = + + O O = compound carbon hydrogen combustion separates use % in O 2 as conversion factor O O 2 2 by subtraction 2 O use % in 2 O as conversion factor O ombustion analysis use % in O 2 as conversion factor O O 2 2 compound O combustion separates by subtraction compound = + + O O = compound carbon hydrogen 2 O use % in 2 O as conversion factor O 18