1. Lewis Structures and Bonds

2. Compounds
I. Elements join together to form compounds by transferring or sharing electrons
A. Ionic compounds – transfer electrons to reach an octet
B. Covalent compounds – share electrons to reach an octet
1. Valence electrons are the electrons that matter.
II. Lewis Structures – visual representation of the way atoms create bonds

3. A. Ionic Lewis Structures
1. Draw element symbols
2. Place x’s around each symbol to represent valence electrons
3. Show movement of electrons from metal to nonmetal
4. Rewrite ions showing new valence electron counts

4. B. Steps to drawing Lewis Structures
1. Add up all valence electrons
2. Draw compounds
a. Place first element in center, attaching all remaining elements around it by a line
**hydrogen can never be a central atom
3. Begin placing electrons around the outer elements, giving them 6 x’s
**hydrogen will never have x’s around it

5. 4. Place any remaining x’s on the central atom
5. Check each atom to ensure it has 8
a. If an atom does not have its octet, take 2 unshared pair from an attached atom and turn them into a bond (line)
**can create double or triple bonds as needed
Exceptions to be aware of:
1. Hydrogen – maximum of 2 electrons
2. Boron – will have 6 electrons as a central atom

6. 3. Period 3 on nonmetals- can hold a
3. Period 3 on nonmetals- can hold a maximum of 12 electrons by filling their empty d sublevels
Ex. SO3
S = 6 valence electrons
O = 6 valence electrons times 3
Total = 24 valence electrons
O S O O
X X
X X X X
X X
X X X X
X X

7. Molecular Shapes
A. Bond angles – angles made by lines joining nuclei of atoms in molecule
B. Angles and bond lengths predict shape
Ex. CH4 – central atom bonded to 4 identical atoms (expressed as ABn)
C. VSEPR – valence shell electron pair repulsion model

8. Linear - 180˚ 2.
0 lone pair
2 bond
Ex. O C O
3a.
Trigonal planar - 120˚
0 lone pair
3 bond
Ex.

9. 3b.
Bent °
1 lone pair
2 bonding
Ex.

10. Tetrahedral – 109.5˚
4a.
Ex.
0 lone pair
4 bonding
Trigonal pyramidal – 107°
4b.
1 lone pair
3 bonding
Ex.

11. Bent – 109.5°
4c.
2 lone pair
2 bonding
Ex.

12. 5a.
Trigonal bipyramidal - 120˚
& 90˚
Ex.
0 lone pair
5 bonding

13. 5b.
Seesaw- complex
180°,90° and 120°
1 lone pair
4 bonding
Ex.

14. T-shaped
~90° and ~180°
5c.
2 lone pair
3 bonding
Ex.

15. 5d.
Linear - 180°
3 lone pair
2 bonding
Ex.

16. 6a.
Octahedral
90˚ and 180°
Ex.
0 lone pair
6 bonding

17. 6b.
Square pyramidal
90° and 180°
Ex.
1 lone pair
5 bonding

18. Square planar-
90° and 180°
6c.
2 lone pair
4 bonding
Ex.

19. 9.2 VSEPR Model
A. Bonding pair – define region where electrons will most likely be (electron domain)
B. lone pairing pair (lone pair) – defines an electron domain on 1 atom
C. Multiple bond = domain

20. D. Best arrangement of electrons minimizes repulsion
I. Effect of lone pairing Electrons and Multiple Bonds on Bond Angles
A. Domains for lone pairing electrons pairs exert greater repulsive forces on adjacent domains and compress bond angles

21. B. Multiple bonds exert greater force than single bonds
Single bonds > Double bonds > Triple bonds