Chapter 10 Chemical Bonding - Millersburg Area …

1 Chapter 10 Chemical Bonding 2 Bonding Theories Bonding -- the way atoms attach to make molecules. Bonding can help us: the shapes of molecules and their properties as well. and build molecules with particular sets of Chemical and physical properties. 3 lewis Theory Uses dots to represent valence electrons. Arranges Bonding between atoms to attain certain sets of stable valence electron arrangements. 4 lewis Theory lewis theory emphasizes the importance of valence electrons. Uses symbol of element to represent nucleus and inner core electrons.

2 Uses dots around the symbol to represent valence electrons. Li Be B C N O: :F: :Ne: 5 Example Write the lewis Symbol for Arsenic, As is in column 5A, therefore it has 5 valence electrons. As6 lewis Bonding Theory Atoms bond because it results in a more stable electron configuration. Atoms bond together by either transferring or sharing electrons. Usually this results in all atoms obtaining an outer shell with 8 electrons. Octet rule. some exceptions to this rule Li and Be Ionic Bonds Bonds formed between metals and nonmetals Recall metals lose electrons--- Cations Nonmetals gain electrons--- Anions Therefore electrons must be transferred from atom to another for Bonding to occur 7 8 Example Using lewis Theory to Predict Chemical Formulas of Ionic Compounds Predict the formula of the compound that forms between calcium and chlorine.

3 Draw the lewis dot symbols of the elements. Ca Cl Transfer all the valence electrons from the metal to the nonmetal. Ca Cl Cl Ca2+ ::Cl ::ClCaCl2 9 Covalent Bonds Bond form between two nonmetals. The type of compound formed are known as molecular or covalent compounds Atoms share pairs of electrons to attain octets. Types covalent bonds Single Double Triple 10 Single Covalent Bonds Two atoms share one pair of electrons. F F H F F H O H H O F F 11 Double Covalent Bond Two atoms sharing two pairs of electrons.

4 4 electrons. Shorter and stronger than single bond. O O O O O O 12 Triple Covalent Bond Two atoms sharing 3 pairs of electrons. 6 electrons. Shorter and stronger than single or double bond. N N N N N N Trends in Bond Length and Energy Bond Length (pm) Energy (kJ/mol) C-C 154 346 C=C 134 602 C C 120 835 C-N 147 305 C=N 128 615 C N 116 887 C-O 143 358 C=O 123 799 14 Bonding and Lone Pair Electrons Bonding pairs--Electrons that are shared by atoms Lone pairs-- Electrons that are not shared by atoms but belong to a particular atom Also known as nonbonding pairs.

5 O S O Lone pairs Bonding pairs 15 lewis Structures of Molecules Some common Bonding patterns. C = 4 bonds & 0 lone pairs. 4 bonds = 4 single, or 2 double, or single + triple, or 2 single + double. N = 3 bonds & 1 lone pair. O = 2 bonds & 2 lone pairs. H and halogen = 1 bond. Be = 2 bonds & 0 lone pairs. B = 3 bonds & 0 lone pairs. B C N O F 16 Writing lewis Structures for Covalent Molecules Example: Write the lewis Structure of CO2 17 Write skeletal structure. Most metallic atom central. H terminal.

6 OCO lewis Structure CO2 18 Apply the solution map. Count and distribute the valence electrons. Count valence electrons. C = 4 O = 2 6 Total CO2 = 16 OCO Information: Given: CO2 Find: lewis structure Solution : skeletal electron distribution lewis Example: Write the lewis structure of CO2. C O 1A 2A 3A 4A 5A 6A 7A 8A 19 Count and distribute the valence electrons. C = 4 O = 2 6 Total CO2 = 16 OCO Information: Given: CO2 Find: lewis structure Solution Map: formula skeletal count distribute valence electrons Example: Write the lewis structure of CO2.

7 Start = 16 e- Used = 4 e- Left = 12 e- OCO 20 Count and distribute the valence electrons. Complete octets by distributing to the outside atoms first. C = 4 O = 2 6 Total CO2 = 16 :: OCOI nformation: Given: CO2 Find: lewis structure Solution Map: formula skeletal electron distribution lewis Example: Write the lewis structure of CO2. Start = 16 e- Used = 4 e- Left = 12 e- Start = 12 e- Used = 12 e- Left = 0 e- 21 Count and distribute the valence electrons. Complete octets. If not enough electrons to complete octet of central atom, bring in pairs of electrons from attached atom to make multiple bonds.

8 :: OCOI nformation: Given: CO2 Find: lewis structure Solution Map: formula skeletal electron distribution lewis Example: Write the lewis structure of CO2. Start = 12 e- Used = 12 e- Left = 0 e- ::OCO 22 Writing lewis Structures for Polyatomic Ions Procedure is the same, the only difference is in counting the valence electrons. For polyatomic cations, take away one electron from the total for each positive charge. For polyatomic anions, add one electron to the total for each negative charge. 23 Example NO3 1. Write skeletal structure.

9 N is central because it is the most metallic. 2. Count valence electrons. ONOON = 5 O3 = 3 6 = 18 (-) = 1 Total = 24 e- Example NO3 , Continued 3. Attach atoms with pairs of electrons and subtract from the total. ONOO N = 5 O3 = 3 6 = 18 (-) = 1 Total = 24 e- Electrons Start 24 Used 6 Left 18 24 25 Example NO3 , Continued 3. Complete octets, outside-in. Keep going until all atoms have an octet or you run out of electrons. :::: ONOON = 5 O3 = 3 6 = 18 (-) = 1 Total = 24 e- Electrons Start 24 Used 6 Left 18 Electrons Start 18 Used 18 Left 0 26 Example NO3 , Continued 5.

10 If central atom does not have octet, bring in electron pairs from outside atoms to share. Follow common Bonding patterns if possible. :::: ONO|O :::: ONOOE xamples lewis Structures NClO H3BO3 NO2-1 H3PO4 SO3-2 P2H4 OPOOOHHH OSOO ONO 18 e- 26 e- 32 e- 14 e- HPPHHH OBOOHHH 24 e- ONCl 18 e- 27 28 Exceptions to the Octet Rule H and Li, lose one electron to form cation. Li now has electron configuration like He. H can also share or gain one electron to have configuration like He.