Chemical Formulas Keynote

Writing Formulas and Naming Ionic & Covalent Compounds©2005 Douglas Gilliland Honors Physical Science @ Sarasota High Sarasota, Florida An atom consist of a positively charged nucleus (protons Atoms of elements are not chemically stable until they have 8 Atoms gain, lose or share electrons with other atoms to be come chemically stable ( have 8 valence electrons ). Eight valence electrons (octet rule). and neutrons) and orbiting electrons. Chemical Compounds Six valence Not chemically stable. electrons. -2 8+ Oxide Ion 8+ Chemically stable. electrons. Oxygen Atom T ypes of Compounds I o n i c - occurs when a metal loses all becomes a cation, nonmetal an anion. C o v a l e n t - two nonmetals share electrons. Neither loses or gains atom becomes and ion. electrons - they share electrons. Neither its valence electrons to a nonmetal. Metal Ionic Compounds Crystalline Lattice Burning Magnesium 2Mg + O2 ! 2MgO 20+ + +2 8+ 20+ + + -2 8+ Oxide Ion Magnesium Atom + Oxygen Atom ! Magnesium Ion Reaction between sodium + chlorine 2Na + Cl2 ! 2NaCl 11+ Sodium Atom + + 17+ Chlorine Atom ! 11+ + + + 17+ Chloride Ion Sodium Ion Ionic Compounds Includes a metal and a nonmetal. Metal loses e- and becomes a cation (+). Nonmetal gains e- and becomes an anion(-). Metal comes first followed by nonmetal. Change the name of the nonmetal to -ide. Examples: nitride, sulfide, fluoride, oxide, bromide, iodide, chloride, telluride, phosphide. Valence electrons are electrons in the outer energy level of an atom. Metals have between 1-3 valence electrons. Nonmetals have between 5-7 valence electrons. Lose e- Gain eAnions (- ions) Cations (+ ions) The valence of an elements is the charge it takes Metal atoms lose electrons and become + ions (cations) Nonmetals gain electrons and become - ions (anions) +1 +2 T ransition Metals Multiple valences when it loses or gains electrons. +3 -4 -3 -2 -1 0 The 5 Steps for writing an ionic compound formula: Write the symbols of the two elements. Write the valence of each as superscripts. Drop the positive and negative signs. Crisscross the superscripts so they become subscripts. Reduce when possible. Formula for boron oxide 1. Write the symbols of the two elements. B O Formula for boron oxide 2. Write the valence for each element. B O +3 -2 Formula for boron oxide 3. Drop the positive & negative sign. B O 3 2 Formula for boron oxide 4. Crisscross the superscripts so they become subscripts. B O 3 2 Formula for boron oxide 4. Crisscross the superscripts so they become subscripts. B O 2 3 Formula for boron oxide 5. Reduce subscripts when possible. B O 2 (not possible here) 3 Examples of Reduction Ca 2S 2 ! CaS Ge 2 O4 ! Ge O2 Be2T 3 ! can’t reduce e Al 3 N 3 ! AlN Sn 2 O4 ! SnO 2 Most T ransition elements have 2 valences. Roman numerals are used in the name to show the valence on the ion. !" 12 $% 13 12 # 14 13 Period 4 Transition Metals () 15 12 &' 13 15 *+ 16 12 (, 16 12 -. 16 12 (/ 16 17 0' 16 Examples: Mn Manganese(IV) Mn +4 +6 Manganese(VI) Iron(III) Copper(II) Fe +1 +2 Iron(II) Fe +3 +2 Cu Copper(I) Cu Examples of T ransition Metals Iron(II) Fe +3 Iron(III) Fe +1 Copper(I) Cu +2 Copper(II)Cu +2 Manganese(II) Mn +4 Manganese(IV)Mn +2 Naming compounds with a transition metal. formula name Fe2 O 3 ZnCl 2 AgCl Cu 3 P 2 PbS2 MnO2 Iron(III) oxide Zinc(II) chloride Silver(I) chloride Copper(II) phosphide Lead(IV) sulfide Manganese(IV) oxide Polyatomic Ions -1 Polyatomic (many atom) ions are covalent molecules with a charge. They behave as if they were a single atom ion. Polyatomic Ions +1 NH4 -1 Ammonium Hydroxide Nitrite Nitrate OH -1 NO2 -1 NO3 -2 SO2 -2 SO3 -2 CO3 -3 PO4 Sulfite Sulfate Carbonate Phosphate determine the formula. The only difference is that when you have more than one of a specific polyatomic ion in a formula you must encase it in parenthesis. T reat polyatomic ions as you would any ion - crisscross to Cation Ca Na Ba +2 Writing Formulas Anion -1 NO3 -3 PO4 Compound Ca(NO3)2 NaOH Ba SO4 Mg +2 +1 +2 Mg 3(PO4)2 OH -1 -2 SO4 cannot change the formula of the polyatomic ion. You can only reduce subscripts outside the parenthesis. As in all ionic compounds you must reduce subscripts, but you Carbonate Compounds with Polyatomic ions -2 CO 3 Phosphate -3 PO4 Aluminum carbonate Al 2( CO 3)3 Calcium carbonate Ca CO 3 Sodium carbonate Na 2CO3 Calcium phosphate Ca3(PO3 )2 Aluminum phosphate AlPO 3 Sodium phosphate Na 3PO4 Water Molecule Covalent Compounds Hydrogen Oxygen Atom Atom Hydrogen Atom Covalent Compounds T nonmetals share electrons so both wo have 8 valence electrons. Exception: H Must use prefixes in the name. Name tells you the formula. Example: N2O4 is dinitrogen tetraoxide. You cannot reduce the formulas!!! Neither takes on a charge - no valence. Reaction between hydrogen + oxygen 2H2 + O2 ! 2H2O 1+ 1+ 2 Hydrogen Atoms + 8+ Oxygen Atom 1+ 8+ Water Molecule 1+ The Space Shuttle Oxygen Hydrogen Water Vapor Exothermic Reaction 2H2 + O2 ! 2H2O Covalent Prefixes Mon - 1 T etra - 4 Di - 2 T -3 ri Pent - 5 Hex - 6 A prefix tells you the number of atoms of that element in the compound. Examples of Covalent N2O3 Carbon tetrahydride CH 4 Phosphorus pentoxide PO 5 disulfur trifluoride S2F 3 Dinitrogen trioxide Compounds Ionic and Covalent Structure Ionic compounds Water form a crystalline lattice - a repeating pattern of ions. B ions N-3 ions +3 H atoms O atom Covalent compounds form individual molecules that are not connected to each other. Boron nitride Naming Binary Compounds Does the compound have a metal? (Metal cation + Nonmetal anion) Ionic Yes Place metal first followed by nonmetal ending in -ide (T Nonmetals) wo Covalent No Contain a T ransition Metal? Place the nonmetal furthest to the left on the periodic table first, then No Yes the other nonmetal ending in -ide. Use Roman Do not use Use prefixes to tell the number of Numerals to tell atoms in the compound Roman the valence of mon(o)-1, di-2, tri-3, tetr(a)-4, Numerals the metal. pent(a)-5, hex-6 Examples: Examples: iron(III) oxide copper(II) chloride manganese(IV) oxide silver(I) chloride sodium chloride magnesium nitride aluminum fluoride beryllium oxide Examples: dinitrogen trioxide, nitrogen trichloride, phosphorus pentoxide, sulfur dioxide carbon tetrachloride, dihydrogen oxide Ionic bonding occurs between a metal and and become cations. Nonmetals gain become anions. Summing up: Ionic a nonmetal. Metals lose all their valence eenough e- to fill their valence level and Always crisscross valences and reduce to Do not use prefixes in the names. Ions form a crystalline lattice. determine the formulas of ionic compounds Covalent bonding occurs when two nonmetals share electrons to fill their valence energy level. Summing up: Covalent Never use valence to determine the formula there isn’t any valence. Since the two atoms share electrons, they do not take on a charge. Always use prefixes in the names. Atoms combine to form individual molecules.