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Chemical Bonds To Bond or Not to Bond? Why do atoms want to bond? (Hint: You already know the answer) To Bond or Not to Bond? Octet rule: all elements want to obtain 8 valence electrons and become stable Metallic Bonding Bond between two metals Produces an alloy Alloy: solid solution of two or more metals (ex: Steel) Ionic Bond Electrostatic attraction: attraction between positive and negative charge Gains or loses valence electrons Bond between a metal and nonmetal Ionic Compound Between a METAL and a NONMETAL Between a POSITIVE and a NEGATIVE ion Ion- a charged atom or group of atoms Charges between metal and nonmetal must equal ZERO Most are CRYSTALLINE solids Naming Ionic Compounds The metal is named just as you see it off the periodic table The nonmetal has the ending dropped and replaced with –ide Practice MgCl2 KCl Be3N Cs2S Writing Ionic Formulas Label the Parts: MgCl2 Steps: 1. Write the Element symbols 2. Write each elements charge 3. Determine subscripts by making overall charge of the compound equal zero! 4. Reduce if possible. All Subscripts (other than 1) must be written Li combines with S Practice K – Br Ca – P Sr – O Li – Cl Sodium fluoride Beryllium iodide Magnesium oxide Polyatomic Ions Polyatomic ions: groups of atoms that have a charge List of Polyatomics given today When using polyatomic ions you must use parenthesis if there is more than 1 of them. Ca(OH)2 Naming Ionic Bonds with Polyatomics Name the metal as always. Name the polyatomic just the way the name is on your list. Ca(OH)2 BaSO4 Na3PO4 (NH4)CO3 Mg(ClO3)2 Writing Formulas Must protect polyatomic with parenthesis if it is more than 1! Calcium carbonate Lithium hydroxide Strontium acetate Potassium chromate Barium nitrate Transition Metals Most Transition metals have multiple oxidation numbers Zn+2, Cd+2, Ag+1 Reverse Exceptions: Pb and Sn need roman numerals Exceptions: Must write transition metals with there oxidation number displayed in parenthesis using roman numerals Example: Iron (II) bromide Roman Numerals One (I) Two (II) Three (III) Four (IV) Five (V) Six (VI) Seven (VII) Eight (VIII) Practice Silver nitride ZnCl2 iron (II) hydroxide CoN Lead (IV) nitrate Fe3N2 Iron (III) bromide PbSO4 Mixed Strontium acetate CoN Copper (III) chromate ZnCl2 Magnesium bromide Na3PO4 Li2O Covalent Bonds Share electrons: all elements want 8 valence electrons (***except H and He want 2 valence electrons***) The sharing of covalent compounds gives them different geometrical shapes Between a NONMETAL and a NONMETAL Two Types: Non-polar- equal sharing of electrons Polar- unequal sharing of electrons Naming Covalent Compounds For covalent compounds both of the nonmetals must have prefixes assigned to represent the number of atoms The second element has a prefix and has the ending changed to -ide One- mono Six- hexa Two- di Seven- hepta Three- tri Eight- octa Four- tetra Nine- nona Five- penta Ten- deca Practice Naming Covalent Compounds CO CO2 N2O5 NF3 Practice Writing Covalent Compounds Iodine pentafluoride Nitrogen tribromide Diphosphorus pentoxide Sulfur hexachloride Diatomic Molecules Molecule: another name for covalent bonds Diatomic molecule: covalent compounds between two of the same atoms Seven N2, H2 you need to know: I2, Br2, Cl2, F2, O2, Lewis Dot for Covalent Compounds Lewis Dot Review: What is a Lewis dot diagram? Draw the Lewis dot for the following: S N C Xe He Lewis Dot for Covalent Compounds What does every element want? We must draw the Lewis dot diagram so every element is SHARING 8 valence electrons (EXCEPT: H only needs 2 valence e-) Covalent compounds can create: Single bonds: one line drawn and represents 2 valence electrons Double bonds: two lines drawn and represents 4 valence electrons Triple bonds: three lines drawn and represents 6 valence electrons Lewis Dot for Covalent Compounds Steps: (NAS) 1. NEED: calculate how many total electrons you will need if everyone had 8 2. AVAILABLE: calculate the electrons you have to work with using your valence electron trend from the periodic table 3. SUBTRACT: Need – Available = how many bonds are needed Examples: VSEPR Theory VSEPR: Valence Shell Electron Pair Repulsion Theory Definition: in covalent compounds the geometric arrangement is determined solely by the repulsions between electron pairs present in the valence electron shell To determine shape you must first draw the Lewis dot diagram VSEPR Shapes Linear 2 bonding atoms (regions) 0 lone pairs Tetrahedral 4 bonding atoms 0 lone pairs Trigonal planar 3 bonding atoms 0 lone pairs Polar vs. Nonpolar Polar In a polar molecule there will be at least one lone pair for the central atom Nonpolar Nonpolar molecule has 0 lone pairs from the central atom Ionic vs. Covalent Ionic Very strong bonds Melt at very high temperatures Crystal structures called salts and many can dissolve in water Covalent Weaker bonds Melt at very low temperatures Most cannot dissolve in water Determine Type of Bond K – Br S–O Si – Cl H–F Se – S H–O Na – Cl Fe – S H–N Ca – I Al – O Mg - Br