1 / 19

Ionic Compounds: Writing Formulas

Learn to write formulas for binary and polyatomic ions with smallest whole-number ratios, using empirical formulas and the criss-cross method. Master the rules through examples and challenges with different oxidation numbers.

jeffreymalone
Download Presentation

Ionic Compounds: Writing Formulas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ionic Compounds:Writing Formulas

  2. Empirical Formulas formulas with smallest whole-number ratio of elements in compound ionic compounds are only written as empirical formulas

  3. Formula Unit simplest ratio of ions in ionic compound examples: • KBr is a formula unit • potassium ions & bromide ions are in a 1-to-1 ratio • AlCl3 is a formula unit • aluminum & chloride ions in 1-to-3 ratio

  4. Na+1 Ca+2 O-2 Al+3 Ag+1 Fe+2 Fe+3 Oxidation Number or State • charge of monatomic ion (right superscript) • some elements form only 1 ion • some elements can form more than 1 ion

  5. Writing Formulas for Binary Ionic Compounds • Write positive ion first • Equal but opposite charges cancel out (no subscripts) • Unlike charges use criss-cross method to determine subscripts

  6. reminder: compounds are electrically neutral therefore the sum of all charges in the compound MUST be 0 (+) and (-) charges must = each other

  7. Equal but Opposite Charges • Na+1 and Cl-1: NaCl +1 + (-1) = 0 • Mg+2 and O-2: MgO +2 + (-2) = 0 • Al+3 and P-3: AlP +3 + (-3) = 0 • Formula: write symbols, (+) FIRST!

  8. try a few formulas: • Li+1 and I-1 • Ca+2 and O-2 • Al+3 and N-3 • K+1 and F-1 • Ba+2 and S-2 LiI CaO AlN KF BaS

  9. Criss-Cross Method charges opposite but NOT equal: • Mg+2 and Cl-1, CROSS and DROP! (# only, forget signs!) • Mg1Cl2 (if subscript is 1, don’t write it!) MgCl2

  10. Check the Math • MgCl2 means 1 Mg+2 and 2 Cl-1 (1)(+2) + (2)(-1) = +2 + -2 = 0 • charges MUST add up to zero!

  11. try these: CaCl2 • Ca+2 + Cl-1 • Na+1 + O-2 • Cs+1 + S-2 • Al+3 + Cl-1 • Al+3 + Se-2 • Mg+2 + F-1 • K+1 + N-3 Na2O Cs2S AlCl3 Al2Se3 MgF2 K3N

  12. of course, it gets more difficult KF • potassium (K) and fluorine (F) • zinc (Zn) and iodine (I) • sodium (Na) and oxygen (O) • magnesium (Mg) and oxygen (O) • aluminum (Al) and oxygen (O) • calcium (Ca) and bromine (Br) • cesium (Cs) and iodine (I) • silver (Ag) and sulfur (S) ZnI2 Na2O MgO Al2O3 CaBr2 CsI Ag2S

  13. and more challenging AuF • gold +1 and fluorine • gold +3 and fluorine • titanium +2 and oxygen • titanium +3 and oxygen • titanium +4 and oxygen • manganese +4 and bromine • manganese +7 and bromine AuF3 TiO Ti2O3 Ti2O4  Ti O2 MnBr4 MnBr7

  14. SO42- CO32- PO43- OH1- POLYATOMIC IONS • Table E: groups of covalently bonded atoms that have a charge (+) or (–) • polyatomic ions have “names” • (-) polyatomic ions can form ionic bonds with (+) metal ions

  15. Ternary Compounds • contain 3 or more elements • usually contain a polyatomic ion: • ifpolyatomic ion is (+) it’s bonded toa (-) non-metal ion or a (-) polyatomic ion • ifpolyatomic ion is (–) it’s bonded to a (+) metal ion or a (+) polyatomic ion

  16. Formulas with Polyatomics • What’s the formula for the compound formed from Al+3 and SCN-1? • charges must add up to zero • write symbols, positive first! • figure out how many of each ion needed Al(SCN)3 **You must use parentheses for more than 1 polyatomic ion**

  17. easy ones with equal but opposite charges: • Na+1 and OH-1 • K +1 and HCO3-1 • Mg+2 and CO3-2 • Li +1 and NO3-1 • Ca+2 and SO4-2 NaOH KHCO3 MgCO3 LiNO3 CaSO4

  18. these are more challenging: Mg3(PO4)2 • Mg+2 and (PO4)-3 • Al+3 and (NO3)-1 • Fe+2 and OH-1 • Hg2+2 and SCN-1 • Mg+2 and HCO3-1 • Al+3 and C2O4-2 Al(NO3)3 Fe(OH)2 Hg2(SCN)2 Mg(HCO3)2 Al2(C2O4)3

  19. more challenging Zn(NO3)2 • zinc + nitrate ion • magnesium + hydroxide ion • lithium + carbonate ion • potassium + sulfate ion • calcium + phosphate ion • beryllium + chlorate ion Mg(OH)2 Li2CO3 K2SO4 Ca3(PO4)2 Be (ClO3)2

More Related