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Chemical Formulas

Chemical Formulas. A combination of symbols that represents the composition of a compound. NH 3 ammonia Fe 2 O 3 rust. Na. Electric charge. Mass number. Atomic number. No. of atoms. :. He:. H∙. :O:. :N:. Li∙. :C:. :F:. Be:. ∙B:. :Ne:. ∙ Al:. :P:. :S:. :Cl:. Mg:. :Si:.

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Chemical Formulas

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  1. Chemical Formulas A combination of symbols that represents the composition of a compound. NH3 ammonia Fe2O3 rust

  2. Na Electric charge Mass number Atomic number No. of atoms

  3. : He: H∙ :O: .. .. :N: . Li∙ :C: :F: Be: ∙B: :Ne: .. ∙Al: . .. :P: :S: :Cl: . Mg: :Si: Na∙ .. :Ar: .. .. Ca: Sc: K∙ :Kr: .. .. :Xe: Rb∙ .. .. :Rn: Cs∙ .. Fr∙

  4. Challenge • Look at the following chemical formulas and try to figure out a rule for bonding. Use what you have learned about electrons and stability to help. CaCl2 Al2O3 K2S NaCl AlF3 H2O MgBr2 MgO SrF2 Hint- draw the elements’ dot notation.

  5. Formation of an ionic bond g electron jumps from Na to Cl electron acceptor (Cl) ions attract meets to form electron donor (Na) neutral pair

  6. structure: smallest building blocks are ions- not molecules! • large numbers of ions can attract to form clusters and eventually crystals an ion pair an ion cluster a crystal lattice

  7. Ions • Cations- positive ions (lose electrons) ex.: Na+ Ca2+ Al3+ • Anions- negative ions (gain electrons) ex.: Cl- O2- • Polyatomic ions- ions made of more than one atom. ex.: NO3- SO42- PO43- • The most frequently occurring version of a polyatomic ion got the name -ate.

  8. Oxidation Number The number of electrons gained, lost, or shared in compound formation. Alkali metals: 1+ Alkali earth metals: 2+ Halogens: 1- Oxygen group: 2-

  9. How would calcium and chlorine combine? CaCl2 Cl Cl Ca

  10. The net charge of a compound should be zero. The total positive charges must equal the total negative charges. How can Na+ combine with O2- to form a neutral compound? You need 2Na+ to combine with one O2-. 2(1+) + 1(2-) = 0

  11. Write the formulas- always put the cation first K+ and N3- K3N Ca2+ and N3- Ca3N2 Ba2+ and NO3- Ba(NO3)2 Criss-cross rule of thumb

  12. Naming binary ionic compounds • Write the cation first • Change the anion ending to –ide Na+ and Cl- form sodium chloride H+ and F- form hydrogen fluoride CaBr2 is calcium bromide

  13. Naming polyatomic ionic compounds • Simply name the cation and the polyatomic ion unchanged. Ex.: NaNO3 is sodium nitrate Zinc carbonate is ZnCO3 Beware there are two polyatomic ions that end with –ide. OH- is hydroxide and CN- is cyanide

  14. Molecular Compounds • A molecule is a neutral group of atoms that are held together by covalent bonds. • The valence electrons are shared by the atoms. • Covalent bonding usually occurs between non-metals. i.e. H2O, CO2, O2, NO

  15. Naming molecular compounds • Use prefixes 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

  16. Examples • P4O10 is tetraphosphorus decoxide • N2O3 is dinitrogen trioxide • As2O5 is diarsenic pentoxide • OF2 is oxygen difluoride - Or use the stock system - • SO2 is sulfur (IV) oxide • SO3 is sulfur (VI) oxide

  17. Ionic or covalent? Name • NaBr • CH4 • Fe2O3 • CO2 • CaO • NH4Cl • SiCl4 ionic Sodium bromide covalent Carbon tetrahydride Iron oxide ionic Carbon dioxide covalent ionic Calcium oxide ionic Ammonium chloride covalent Silicon tetrachloride

  18. Comparing ionic and covalent compounds

  19. Diatomic molecules H2 O2 N2 Cl2 Br2 I2 F2

  20. Empirical Formula • A formula that represents the lowest integral ratio of atoms of the elements in a compound. • C2H4, C3H6, C4H8 all have same empirical formula CH2

  21. Naming acids anion acid name example -ide Hydro- ic HCl hydrochloric acid -ite -ous HNO2 nitrous acid -ate -ic HNO3 nitric acid

  22. H2SO4 HF H3PO4 H2SO3 H2CO3 HNO3 sulfuric acid hydrofluoric acid phosphoric acid sulfurous acid carbonic acid nitric acid Try these

  23. CaBr2 Cr(C2H3O2)3 Calcium bromide Chromium (III) acetate Barium sulfate Copper (I) sulfide Sulfur hexafluoride Cr2(C2O4)3 Hg(CN)2 Cu(ClO4)2 ZnC4H4O6 BaSO4 Cu2S SF6 Chromium (III) oxalate Mercury (II) cyanide Copper (II) perchlorate Zinc tartrate

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