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Compounds

Compounds. A compound is a pure substance that contains two or more elements that are chemically bonded to each other Compounds form when the electrons of two or more elements interact and are composed of either: Molecules Ions. Molecules. Molecule:

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Compounds

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  1. Compounds • A compound is a pure substance that contains two or more elements that are chemically bonded to each other • Compounds form when the electrons of two or more elements interact and are composed of either: • Molecules • Ions

  2. Molecules • Molecule: • A group of atoms combined in definite proportions and held together by strong attractive forces calledcovalent chemical bonds • Covalent bonds are formed when atoms share two or more electrons. • The smallest representative particle of amolecular compound

  3. Molecular Compounds • Molecular compounds • composed of molecules that contain more than one type of atom • Most molecular substances are composed of non-metals only. • Examples: • Water (H2O) • Ethyl alcohol (C2H6O) • Carbon dioxide (CO2) • Ammonia (NH3)

  4. Ionic Compounds • Ionic compounds are composed of ions(both cations and anions) and usually contain a metal and one or more nonmetals. • “Salt” (NaCl) • Contains Na+ and Cl- ions • Tums (CaCO3) • Contains Ca2+ and CO32- ions • Milk of Magnesia [Mg(OH)2] • Contains Mg2+ and OH-

  5. Ionic Compounds • Ionic compounds such as NaCl are formed when • one or more electrons are transferred from one atom to another • the resulting cation and anion are strongly attracted to each other and are held together by anionic bond resulting from electrostatic forces of attraction

  6. Chemical Formulas • The composition of a compound is generally shown using a chemical formula: • A shorthand notation that describes the types and relative (or exact) numbers of each atom (or ion) present in a pure substance • Chemical formulas always contain: • Elemental symbols • Subscripts • Show the relative (or exact) number of each type of atom or ion

  7. Chemical Formulas • Molecular Formula • chemical formula that tells the actual number of each type of atom in a molecule • Empirical Formula • chemical formula that tells the smallest whole number ratio of each type of atom in a molecule Acetic Acid C2H4O2 CH2O Ascorbic Acid C6H8O6 C3H4O3 Sodium Sulfate Na2SO4

  8. Ionic Compounds • The ions present in an ionic compound can be either: • Monoatomic • Polyatomic • Monoatomic ion: • a charged species containing a single atom that has gained or lost electrons • Al3+ • S2-

  9. Predicting Ion Charge – Monoatomic Ions • Many atoms gain or lose electrons in such a way that they end up with the same number of electrons as the nearest (closest in atomic number) noble gas. • “octet” rule Ca (20p, 20e-)  Ca2+ (20p, 18e-) [Ar: 18p,18e-] O (8p, 8e-) O2- (8p, 10e-) [Ne: 10p, 10e-]

  10. Predicting Ion Charge – Monoatomic Ions • Using the octet rule you can easily determine the charge on most of the monoatomic ions formed by the main group elements. • Main group metal cations: • Charge = group number • Main group nonmetal anions: • Charge = group # - 8 (or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)

  11. Common Monoatomic Ions Know These! P3- Zn2+ Ag+ In general: Metal atoms and hydrogen lose e- and form cations. Nonmetal atoms gain e- and form anions.

  12. Main group Cr2+ Cr3+ Mn2+ Mn3+ Fe2+ Fe3+ Co2+ Co3+ Cu+ Cu2+ Main group Sn2+ Sn4+ Pb2+ Pb4+ Bi3+ Bi5+ Common Monoatomic Ions Many transition metals and a few main group elements form more than one ion.

  13. Names of Monoatomic Ions - Cations • Cations formed by a metal have the same name as the metal. K+ potassium ion Ca2+ calcium ion Al3+ aluminum ion • If a metal forms more than one cation, use Roman numerals in ( ) after the name of the metal to show its charge. Fe2+ iron (II) ion Fe3+ iron (III) ion Cu+ copper (I) ion Cu2+ copper (II) ion

  14. Names of Monoatomic Ions - Anions • Monoatomic anions are named by: • dropping the ending of the element’s name • adding “ide” N nitrogen O oxygen N3- O2- nitride oxide

  15. Polyatomic Ions • Polyatomic ion: • an electrically charged group of two or more atoms that are held together by covalent bonds • Polyatomic ions cannot be broken into smaller pieces. • Examples: • NO3- • SO42- • HCO3- • PO43-

  16. Polyatomic Ions • You are responsible for knowing the names and formulas of all ions listed in your syllabus, including the common polyatomic ions: • Ammonium NH4+ • Hydroxide OH- • Cyanide CN- • Nitrate NO3- • Acetate C2H3O2- • Sulfate SO42- • Bisulfate (Hydrogen sulfate) HSO4- • Carbonate CO32- • Bicarbonate (Hydrogen carbonate) HCO3- • Phosphate PO43-

  17. Naming Oxyanions • Many of the polyatomic anions are oxyanions. • polyatomic anions containing one or more oxygens attached to a central atom • To name an oxyanion, drop the ending of the central atom name and add: • “ate” most common oxyanion of the element • “ite” 1 less oxygen NO3- nitrateSO42- sulfate NO2- nitrite SO32- sulfite CO32- carbonatePO43- phosphate PO33- phosphite

  18. 3A 4A 5A 6A 7A Noble gases Oxyanions “ate” oxyanions to memorize

  19. Oxyanions • The halogens typically form 4 different oxyanions: • “per” 1 more O than the “ate” oxyanion • “hypo” 1 less O than the “ite” oxyanion ClO4- perchlorate most oxygens ClO3- chlorate most common ClO2- chlorite 1 less O ClO- hypochlorite fewest oxygens

  20. Oxyanions • Anions derived by adding one or two H+ to an oxyanion: • add “hydrogen” or “dihydrogen” as prefix to oxyanion name CO32- carbonate HCO3- hydrogen carbonate (usually called bicarbonate) PO43- phosphate H2PO4- dihydrogen phosphate

  21. Writing Formulas for Ionic Compounds • Ionic compounds are always represented using an empirical formula with the cation shown first. • The formula for an ionic compound must be electrically neutral. • Total positive charge = total negative charge • Although ions are present in an ionic compound, the formula does NOT explicitly show the charge of the ions.

  22. Na+ Na+ Cl- Writing Formulas for Ionic Compounds • Ionic compounds must be electrically neutral. • Total positive charge = total negative charge Na+ + Cl- NaCl (1 pos, 1 neg)

  23. Cl- Cl- Ca2+ Ca2+ Ca2+ + 2Cl- CaCl2(2 pos, 2 neg) Cl- Writing Formulas for Ionic Compounds Ca2+ + Cl- CaCl (2 pos, 1 neg)

  24. Writing Formulas for Ionic Compounds • To write the empirical formula of an ionic compound from its name: • Identify the formula including charge for each ion. • Combine the ions in a ratio that gives an electrically neutral compound.

  25. Na+ HCO3- Ca2+ SO42- Writing Formulas for Ionic Compounds • If charges on the ions are equal in magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.

  26. Writing Formulas for Ionic Compounds • If charges on the ions are different, then flip-flop the charges (i.e. the charge of one ion becomes the subscript of the other ion). • Place ( ) around all polyatomic ions IF more than one is needed.

  27. Writing Formulas for Ionic Compounds Example: Write the correct formula for the following ionic compounds. • Zinc bromide • Aluminum carbonate • Iron (II) phosphate • Tin (IV) sulfate • Magnesium hydroxide

  28. Writing Formulas for Ionic Compounds Example: Write the correct formula for the following ionic compounds. • Sodium bicarbonate • Ammonium sulfate • Potassium phosphite • Sodium hypochlorite • Copper (I) oxide

  29. Writing Formulas for Ionic Compounds • Remember: • Use empirical formulas • Formulas must be electrically neutral • Do not show the charges of each ion in the final formula that you write • Use parentheses around polyatomic ions if more than one is present in the formula • Do not use ( ) around monoatomic ions • Do not use ( ) around a single polyatomic ion

  30. Naming Ionic Compounds • Ionic compounds are named using the cation name followed by the anion name CaBr2 calcium bromide NaClO sodium hypochlorite Mg3(PO4)2 magnesium phosphate • If the cation can form ions with more than one charge, you must specify the charge: Fe2S3 iron (III) sulfide PbO2 lead (IV) oxide

  31. Naming Ionic Compounds Example: Name the following ionic compounds. • Na2SO4 • FeCl3 • (NH4)3PO4 • KClO4 • Cu2CO3 • Sn(SO4)2

  32. Common “Household” Chemicals • You are responsible for knowing the names and formulas for the chemical present in: • Baking soda • sodium bicarbonate • NaHCO3 • Table salt • Sodium chloride • NaCl • Bleach • Sodium hypochlorite • NaClO or NaOCl

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