Chapter 12 CHEMICAL BONDING

Transcription

1 Chapter 12 CHEMICAL BONDING Sharing electrons is fun! H F Do you smell what the Rock is cooking? I. Types of Chemical Bonds A. Formation of Covalent Bonds B. Lewis Symbols and Covalent Bonding C. Other Types of Covalent Bonds II. Molecular Compounds and Lewis Structures A. Drawing Lewis Structures 1. Resonance Structures 2. Exceptions to the Octet Rule III. The Shapes of Molecules A. VSEPR Theory B. Bond Polarity and Molecular Polarity

2 I. Types of Chemical Bonds 1 Review of Ionic and Covalent Bonds Ionic Compounds Ionic Bonds - transfer of electrons between atoms metal - non-metal Molecular Compounds Covalent Bonds - sharing of electrons between atoms non-metal - non-metal Example CH 3 CH 2 OH

3 A. Covalent Bonding in more Detail 2 How do atoms interact? - They share electrons Which electrons can be shared? - valence electrons (outer s & p orbitals) Observations atoms react until they obtain a noble gas core Octet Rule most atoms share electrons until they are surrounded by 8 valence electrons Duet Rule Hydrogen and Helium share electrons until they are surrounded by 2 electrons Lewis Symbol chemical symbol for element + a dot for each valence electron

4 Group Element E.C. Valence Electrons Lewis Symbol 1A H 1s 1 2A Be [He]2s 2 3A B [He]2s 2 2p 1 4A C [He]2s 2 2p 2 5A P [Ne]3s 2 3p 3 6A S [He]2s 2 2p 4 7A Br [Ar] 4s 2 3d 10 4p 5 8A Kr [Ar] 4s 2 3d 10 4p 6

5 B. Lewis Symbols and Covalent Bonds 3 Covalent Bond - involves the sharing of electrons between two atoms Lewis Structure - structure obtained by combining Lewis symbols to create covalent bonds Example Lewis Structure for F 2

6 C. Other Types of Covalent Bonds 4 Multiple Covalent Bonds - covalent bond formed by the sharing of more than 2 electrons (in multiples of 2) Single bond Double bond Triple bond Example O 2 and CO

7 II. Lewis Structures in Detail Requirements and Trends for L.S. 1. L.S. must include all valence e- - + ion subtract e- - - ion add e Usually e- are paired 3. Octet rule is usually followed, most notable exception H (duet) 4. Trends

8 Electronegativity

9 A. Rules for Writing Lewis Structures 1. Sum all of the valence electrons from all of the atoms 7 2. Draw the skeleton structure of the molecule using one pair of electrons (= one single bond) for each connecting bond. (If there is a central atom it is usually written first in the formula: CO 2 C is the central atom) 3. Determine the amount of electrons used and the number of electrons left over mlbyrf.wordpress.com

10 4. Distribute the remaining electrons to achieve a noble gas configuration (octet) on each atom: 1) How many are needed? 2) How many are available? 8 -If needed = available distribute as lone pairs -If needed > available make one additional bond for every 2 electrons short and distribute remaining electrons as lone pairs

11 5. Skeletal Structure - arrangement of atoms in molecule Central atom bonded 2 or more atoms Terminal atom bonded to 1 atom - H-atoms are always terminal - Carbon atoms are almost always central atoms - central atoms generally have the lowest electronegativity - More compact and symmetrical the better examples CH 3 CH 2 OH 6 CO

12 Example: Step 1 Sum the valence electrons Step 2 Draw the skeleton using single bonds Step 3 Determine the # of electrons left Need = avail. Need > avail. Step 4 Distribute remaining e- to achieve noble gas config. on each atom

13 Example: Step 1 Sum the valence electrons Step 2 Draw the skeleton using single bonds Step 3 Determine the # of electrons left Need = avail. Need > avail.

14 Example: Step 1 Sum the valence electrons Step 2 Draw the skeleton using single bonds Step 3 Determine the # of electrons left Need = avail. Need > avail. Step 4 Distribute remaining e- to achieve noble gas config. on each atom

15 Example: Step 1 Sum the valence electrons Step 2 Draw the skeleton using single bonds Step 3 Determine the # of electrons left Need = avail. Need > avail. Step 4 Distribute remaining e- to achieve noble gas config. on each atom

16 Example: Step 1 Sum the valence electrons Step 2 Draw the skeleton using single bonds Step 3 Determine the # of electrons left Need = avail. Need > avail. Step 4 Distribute remaining e- to achieve noble gas config. on each atom