Transcript 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 water = H O H Ions Salt = NaCl Na , Cl Molecules Molecule: A group of atoms combined in definite proportions and held together by strong attractive forces called covalent chemical bonds Covalent bonds are formed when atoms share two or more electrons. The smallest representative particle of a molecular compound 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) 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- 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 an ionic bond resulting from electrostatic forces of attraction 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 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 Ascorbic Acid Sodium Sulfate C2H4O2 C6H8O6 Na2SO4 CH2O C3H4O3 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- 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-] 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) Common Monoatomic Ions Know These! P3Zn2+ Ag+ In general: Metal atoms and hydrogen lose e- and form cations. Nonmetal atoms gain e- and form anions. Common Monoatomic Ions Many transition metals and a few main group elements form more than one ion. Main group Main group Cr2+ Mn2+ Fe2+ Co2+ Cr3+ Mn3+ Fe3+ Co3+ Cu+ Cu2+ Sn2+ Sn4+ Pb2+ Bi3+ Pb4+ Bi5+ 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+ Fe3+ Cu+ Cu2+ iron (II) ion iron (III) ion copper (I) ion copper (II) ion Names of Monoatomic Ions - Anions Monoatomic anions are named by: dropping the ending of the element’s name adding “ide” N N3- nitrogen O oxygen nitride O2- oxide 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 SO42HCO3 PO43- H H N H H Polyatomic Ions You are responsible for knowing the names and formulas of all ions listed in your syllabus, including the common polyatomic ions: Ammonium Hydroxide Cyanide Nitrate Acetate Sulfate Bisulfate (Hydrogen sulfate) Carbonate Bicarbonate (Hydrogen carbonate) Phosphate NH4+ OHCNNO3C2H3O2SO42HSO4CO32HCO3PO43- Naming Oxyanions mXOn 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- nitrate NO2- nitrite SO42- sulfate SO32- sulfite CO32- carbonate PO43- phosphate PO33- phosphite Oxyanions “ate” oxyanions to memorize 4A 5A 2CO3 NO3 carbonate 6A nitrate 3PO4 2SO4 phosphate sulfate 7A - ClO3 chlorate BrO3 bromate IO3 iodate Noble gases 3A Oxyanions The halogens typically form 4 different oxyanions: “per” “hypo” 1 more O than the “ate” oxyanion 1 less O than the “ite” oxyanion ClO4ClO3ClO2ClO- perchlorate chlorate chlorite hypochlorite most oxygens most common 1 less O fewest oxygens Oxyanions Anions derived by adding one or two H+ to an oxyanion: add “hydrogen” or “dihydrogen” as prefix to oxyanion name CO32HCO3- carbonate hydrogen carbonate (usually called bicarbonate) PO43H2PO4- phosphate dihydrogen phosphate 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. NaCl not Na Cl Writing Formulas for Ionic Compounds Ionic compounds must be electrically neutral. Total positive charge = total negative charge Na+ + Cl- NaCl Na+ Cl- (1 pos, 1 neg) Writing Formulas for Ionic Compounds Ca2+ + Cl- CaCl (2 pos, 1 neg) ClCa2+ Ca2+ + 2Cl- CaCl2 (2 pos, 2 neg) ClCa2+ Cl- Writing Formulas for Ionic Compounds To write the empirical formula of an ionic compound from its name: 1. Identify the formula including charge for each ion. 2. Combine the ions in a ratio that gives an electrically neutral compound. 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. calcium sulfate 2+ Ca 2SO4 Ca2+ SO42- CaSO4 sodium bicarbonate + Na - HCO3 NaHCO3 Na+ HCO3- 3- 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). magnesium nitride Mg2+ N3- Mg3N2 calcium hydroxide 2+ Mg3N Ca 2 OH 1- Ca(OH)2 Place ( ) around a polyatomic ion IF more than one is needed. 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 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 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 Naming Ionic Compounds Ionic compounds are named using the cation name followed by the anion name CaBr2 NaClO Mg3(PO4)2 calcium bromide sodium hypochlorite magnesium phosphate If the cation can form ions with more than one charge, you must specify the charge: Fe2S3 PbO2 iron (III) sulfide lead (IV) oxide Naming Ionic Compounds Example: Name the following ionic compounds. Na2SO4 FeCl3 (NH4)3PO4 KClO4 Cu2CO3 Sn(SO4)2 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