1. 7.5 NOTES Exceptions to the Octet Rule

2. B. Resonance structures –Certain molecules that are composed of single AND double bonds can be written in two different ways
- For example - O3.
- If one is chosen over another it presents the problem of determining bond length; the single bond is longer than the double bond, but it has been proven both bonds in ozone have the same length
- Answer – use both structures to represent the molecule; known as resonance structures

3. - RS – 1 of 2 or more Lewis structures for a single molecule that cannot be described fully with only 1 Lewis structure
- Resonance – the use of 2 or more Lewis structures to represent a particular molecule;

5. C. Exceptions to the octet rule
1. Odd electron species, e.g. NO or NO2
- Small number of molecules will have an odd number of electrons and therefore cannot form an octet
- ALL OF SERIES 2 CAN NEVER HAVE MORE THAN 8 ELECTRONS

6. 2. Fewer than 8 electrons. BH3 is the best example.
Coordinate covalent bond: A covalent bond in which one of the atoms donates both electrons; some compounds have fewer than 8 electrons and tend to be reactive
BH3 bonds with NH3, with NH3 donating both electrons creating a coordinate covalent bond
atoms or ions with lone pairs often form coordinate bonds; B, H, and halogens can never make a double bond b/c lack the # of orbitals
Examples: BeH2 H – Be – H; Be configuration 1s22s2; BX3 where X is a halogen

8. 3. Expanded octet.
Larger atoms (series 3 and beyond) can hold more than 8 e-. P, S, and As commonly have 10 or 12 e- around them.
Elements in (and beyond) the 3rd series have d orbital electrons that can be used in bonding as well as s and p
SF6 is an example  each of sulfur’s valence electrons will form a covalent bond with a fluorine atom giving S twelve electrons