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Writing Chemical Formulas Also assigned www.ChemThink .com Ionic Bonding and Ionic Formulas Tutorial and questions Ions • When as atom gains or loses an atom is called an ion. • Cation if positively charged or giving electrons away. • • Anion if negatively charged or accepting electrons. How to predict charges with Lewis Dot All elements move to have a full outer octet, like the Noble Gasses. An outer octet is made from 2 electrons in the s orbit and 6 electrons in the p orbit. Elements can gain or lose electrons to achieve 8 electrons in their valence shell. H + H + e = e More Examples: F + N +3 e + 4 C e C e F N C 4+ C +4e 34- General Charges X X +1 +2 X X X X X X Many different Charges +4 +3 -3 -2 -1 -4 Many Different Charges N O B E L G A S E S Writing Compounds: Sodium and oxygen… Na O Na+1 and O2These need to add together to equal zero. One must lose electrons and the other must gain electrons. So two sodium’s for every oxygen to equal zero. 2(+1) + (-2) = 0 2 Na+1 and O2- This is written Na2O. Example #2: Barium and phosphorous Ba P Ba2+ and P3These must add to equal 0. Therefore 3 bariums and 2 phosphorous are needed. 3(+2) + 2(-3) = 0 3 Ba2+ and 2 P3This is written Ba3P2 Polyatomic ions • These are groups of atoms that hang around together and have a charge. Hydroxide ion Ammonium ion Here is a trick to name and know about 48 polyatomic ions. BO3 CO3 NO3 Now to name them… Like the chart above (base element name) –ate 1 more oxygen than above Per -(base element name) – ate 1 less oxygen than above (base element name –ite 2 less oxygen than above Hypo –(base element name) - ite -2 -1 O F PO4 SO4 ClO3 AsO4 SeO4 BrO3 SbO4 TeO4 IO3 Noble Gases -3 -3 -2 -1 As is… BO3 CO3 NO3 BO33- borate CO32- carbonate PO4 SO4 ClO3 – NO3 nitrate PO43- phosphate AsO SeO BrO 4 4 3 2SO4 sulfate Lose one oxygen – ClO3 chlorate… make you want SbO TeO IO O to fight… NO2– nitrite ClO2– chlorite BO23- borite CO22- carbonite PO33- phosphite SO32- sulfite… 4 F 4 3 Noble Gases Polyatomics Lose two oxygens and you are out in the cold but still want to fight. ClO– hypochlorite BO 3- hypoborite CO2- hypocarbonite NO– hyponitrite PO23- hypophosphite SO22- hyposulfite… -3 BO3 CO3 NO3 Gain one oxygen make you want to per… ClO4– perchlorate BO43- perborate CO42- percarbonate NO4– pernitrate PO53- perphosphate SO52- persulfate… -2 -1 O F PO4 SO4 ClO3 AsO4 SeO4 BrO3 SbO4 TeO4 IO3 Noble Gases Polyatomics Other polyatomics that you should know are on the back of your periodic table that you were given. Writing Formulas with polyatomics. Let’s write the formula for sodium and phosphate. Na+ PO4 3Remember that these must add to equal zero. 3 (+1) + 1 (-3) = 0 3 Na+ 1 PO4 3- Na3PO4 Writing Formulas with polyatomics. Let’s write the formula for calcium and nitrate. Ca2+ NO3 Remember that these must add to equal zero. 1 (+2) + 2 (-1) = 0 1 Ca2+ 2 NO3- Because there are two nitrates needed to balance out the charge of the calcium parenthesis are used to keep the group together and denote that two groups of nitrate are needed to balance the charge of the calcium. Ca(NO3)2 Writing Formulas with polyatomics. Let’s write the formula for barium and phosphate. Ba2+ PO4 3Remember that these must add to equal zero. 3 (+2) + 2 (-3) = 0 3 Ba+ 2 PO4 3- Because there are two phosphates needed to balance out the charge of three bariums parenthesis are used to keep the group together and denote that two groups of phosphate are needed to balance the charge of the three bariums. Ba3(PO4)2 Writing Formulas with polyatomics. Let’s write the formula for lead (IV) carbonate. The Roman Number (IV) tells the charge of the lead. The Roman number always tells the charge of the positive ion. Pb4+ CO32Remember that these must add to equal zero. Careful! This must happen with the lowest numbers possible! 1 (+4) + 2 (-2) = 0 1Pb4+ 2 CO32- Because there are two carbonate ions needed to balance out the charge of on lead (IV) ion parenthesis are used to keep the group together and denote that two carbonate ions are needed to balance the charge of the lead (IV) ion . Pb(CO3)2 Writing Formulas with polyatomics. Let’s write the formula for aluminum and oxalate. Al3+ C2O4 2Remember that these must add to equal zero. 2 (+3) + 3 (-2) = 0 2 Al3+ 3 C2O4 2- Because there are three oxalate ions needed to balance out the charge of two aluminum parenthesis are used to keep the group together and denote that three groups of oxalate are needed to balance the charge of the two aluminum. Al2(C2O4)3 Keep Practicing! Keep Up! Don’t forget to take notes!