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WVU CHEM 115 - Lecture 5

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Molecular vs. Ionic Compounds • Molecular: based on sharing of electrons between atoms known as a covalent bond. Characteristics: poor electrical conductors; small molecules may be gas, liquid or soft solids. • Ionic: based on electrostatic attraction between positive and negative ions (atoms or groups of atoms with a charge) known as an ionic bond. Characteristics: good electrical conductors if the ions are mobile (liquids, solutions). Tend to be hard, brittle, often with high melting points. Classification of Chemical Compounds: Molecular vs. Ionic Molecular/Covalent Compounds • Formed by combination of two or more nonmetals. Ex. CH4, SiH4, PH3, CO2 • Consist of discrete molecules that move about as a unit. • Molecule is the smallest bit of a molecular compound. • Chemical formula referred to as molecular formula. • Covalent bonds hold together the atoms in the molecule. Ionic Compounds • Formed by combination of cation (metal or polyatomic) with an anion (nonmetal or polyatomic). Ex. KCl, AlBr3 , Mg3(PO4)2 • Consist of three dimensional array of ions such that no particular cation belongs to a particular anion. • Formula unit is the smallest bit of an ionic compound. • Chemical formula referred to as the formula unit. • Ionic bonds hold the ions together.Molecules of the molecular compound H2O. 3-D array of ions in the ionic compound NaCl. Na  Na+ + 1 e- 11p 11p 11e- 10e- Cl + 1 e-  Cl- 17p 17p 17e- 18e- Molecular vs. Ionic Compounds Molecular or Ionic? Identify whether these formulas represent molecular or ionic compounds: • C2H6O (all non-metal atoms – molecular) • LiBr (metal + non-metal – ionic) • CaBr2 • CH3COSH • Al2O3 • COCl2 • CoCl2Formula Unit Chemical formula for an ionic compound. Subscripts specify the smallest whole number ratio of cation to anion to give a neutral compound. • Examples: Give formula units for ionic compounds formed by combination of the elements or ions below. sodium and fluorine ammonium and sulfate calcium and sulfur potassium and carbonate Nomenclature “The naming of chemical compounds.” Organic Compounds: hydrocarbons (molecules containing H and C) and their derivatives. Ex. CH4, C8H18, CH3OH Inorganic Compounds: all other compounds. Ex. NaCl, PBr3, FeO, CS2 Naming of Inorganic Compounds A. Classify the compound: Is the compound ionic, molecular, or an acid? Note: H usually written first in the chemical formula of an acid. 1. Naming of ionic compounds. a. Metal cation with NONVARIABLE charge. i. Name the metal (or cation) first. ii. Name the nonmetal (or anion) second. iii. Change ending of nonmetal to –ide. NOTE: Don’t change ending of polyatomics!!Examples: Provide names for the following ionic compounds. CaO K2S Mg3P2 (NH4)3PO4 b. Metal cation with VARIABLE charge (transition or post- transition metal). STOCK SYSTEM: i. Name the metal (or cation) first. ii. Specify charge on metal using Roman numeral inside parentheses. iii. Name nonmetal and change ending to –ide. or OLD SYSTEM: i. Name the metal first using the Latin name. ii. Specify charge on metal by changing ending…. -ous metal cation of lower charge -ic metal cation of higher charge iii. Name nonmetal and change ending to –ide. Examples: Provide names for the following ionic compounds using both the STOCK and OLD system. (Latin names for some metals: ferrum, cuprum, stannum, plumbum, aurum, stibium) STOCK OLD CuCl CuCl2 Fe(NO2)2 Fe(C2H3O2)32. Naming of molecular/covalent compounds. a. Name the element that comes first in chemical formula first. (Usually this element lies farthest to left in periodic table) b. Name the second element and change ending to –ide. c. Specify number of atoms of each element present by addition of a Greek number prefix. Number Greek Prefix 1 mono- (often omitted) 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca- Provide names for the following molecular compounds. A. Cl2O7 B. Cl2O C. N2O5 D. N2O E. CO F. CO23. Naming of acids with (aq) designation. (H usually written first in chemical formula of acid.) a. Decide whether acid is a BINARY or OXYACID. Binary Acid – contains H and one other element. Ex. HCl(aq), HF(aq), H2S(aq) Oxyacid – contains H, O, and one other element. Ex. HClO4, H2SO3, HNO2 b. Naming of binary acids. i. Use root of nonmetal name. ii. Add hydro- prefix and –ic suffix to root. Examples: Provide names for the following binary acids. HCl(aq) HF(aq) HBr(aq) c. Naming of oxyacids. i. Use root of nonmetal name followed by acid. ii. If only two different oxyacids can be formed from nonmetal, specify which is present by adding following suffixes. -ous oxyacid with least oxygens -ic oxyacid with most oxygens iii. If four different oxyacids can be formed from nonmetal, specify which is present by adding following prefixes and suffixes. hypo- -ous oxyacid with least oxygens -ous -ic per- -ic oxyacid with most oxygens4. Naming of polyatomic ions. Most polyatomic ions are anions derived from oxyacids by removal of one or more protons (H+). a. -ous ending of oxyacid is changed to –ite when H+ removed. -2 H+ Ex. H2SO3 SO3-2 sulfurous acid sufite anion b. -ic ending of oxyacid is changed to –ate when H+ removed. -H+ Ex. HClO4 ClO4- perchloric acid perchlorate anion Example: Provide names for the following oxyacids. HBrO H2SO4 HBrO2 HNO2 HBrO3 HBrO4 Special Case: Mercury Cations • The mercury I cation is a special case; it consists of two Hg+ ions joined together, and so is always found as Hg22+. While the entire ion has a +2 charge, each Hg has a +1 charge. • Hg22+


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