Bonding

Question 1

Ionic character

Answer 1

the percentage of difference in electronegativity between two covalently bonded atoms

Question 2

Formal charge formula

Answer 2

Formal charge = valence of the atom – ½ # bonding e–s – # nonbonding e–s

Question 3

Formal charge rules

Answer 3

1. the sum of all formal charges must equal the overall
   charge of the species
2. minimal formal charges (+1, –1) are always better than
   excessive formal charges (±2, ±3…etc.)
3. when unavoidable, negative formal charges should
   reside on most electronegative atoms (F, O, N…)

Question 4

What are exceptions to the Octet rule

Answer 4

Odd-Numbered Valences
Incomplete Octets
Expanded Octets

Question 5

Odd-Number Valences

Answer 5

• aka radicals or free radicals
• highly reactive and unstable species
• they occur when there is an odd-number of valence
  electrons due to the presence of an odd-number of Group
  5A and/or 7A elements
• usually place the single electron on the atom that minimizes formal charges
• examples: NO, ClO

Question 6

Incomplete Octets

Answer 6

some atoms are satisfied having less than eight electrons in their outer valence shell
* beryllium (Be): four electrons in outer shell
* boron (B): six electrons in outer shell

Question 7

Expanded Octets

Answer 7

Period 3 atoms (P, S, Cl…) and
beyond (As, Se, Br, Kr, I, Xe…) can
expand their octets and
accommodate more than eight
electrons in their outer shell
* due to easy access to relatively low
energy d-orbitals
* if they can, atoms will expand
their octets to reduce formal
charges

• PERIOD 2 ATOMS (C, N, O, F)
  NEVER EXPAND THEIR OCTETS
• the cardinal sin of Lewis structures!
• no d-orbitals for Period 2