chap 4 notes

Identifying Central and Surrounding Atoms
- Use electronegativity to determine the central atom.
- The atom with lower electronegativity should be the center.
- The atom with higher electronegativity should surround the center.
- Exception: Hydrogen can never be a central atom regardless of electronegativity.
Example:
- For the compound involving Phosphorus (P) and Chlorine (Cl):
- Central Atom: Phosphorus (P) due to one phosphorus atom surrounded by five chlorine atoms.
- Logic: One P cannot surround five Cl atoms; instead, five Cl will surround one P.
- Positioning of Chlorines: The arrangement of chlorines around the phosphorus does not affect the structure.

Connect all surrounding atoms to the central atom with a single line (bond).
Completing this step results in a skeleton structure for the compound.

Goal: Show the distribution of valence electrons among the atoms.
Start assigning electrons from surrounding atoms first; central atom is assigned last.
Each atom aims for eight valence electrons (octet rule) to be considered full/happy, except for hydrogen which seeks only two (duet rule).
Count Total Valence Electrons:
- Remember that when drawing the skeleton, some valence electrons are used for bonding.
- For example, if a molecule has 40 total valence electrons, 10 are used in bonding (5 bonds); therefore, only 30 remain for assignment.
Assigning Electrons to Chlorine:
- Chlorine atoms need 6 more electrons (from a total of 8) to fulfill the octet rule.
- Use dots to represent electrons (do not use stars).
- Electrons should be assigned in pairs.
Finish assigning all surrounding atoms before moving to the central atom.
- This analogy compares the care of helping one “be happy” before moving to assist others in need.
After dispersing assigned electrons, check if total valence assigned equals the original count.

After all valence electrons are assigned, ensure each atom is happy (has the required number of electrons).
If any atom (including the central atom) is not happy, adjustments must be made to balance electron counts by sharing through bonding.

Hydrogen: Can only achieve 2 electrons; this is termed the duet rule.
Boron: Can be happy with either 6 or 8 electrons.
Phosphorus (P) and Sulfur (S): Can have more than 8 electrons if more electrons are available.

Count total valence electrons.
Draw the skeleton structure (identify center and surrounding atoms).
Assign remaining valence electrons to the surrounding atoms first, central atom last.
Check if all atoms are happy (satisfied with the electron counts).
Make necessary adjustments through sharing if needed.

Identifying Central Atom: Carbon is the central atom, and hydrogen cannot be the center.
Count Valence Electrons:
- Carbon (C): 4 valence electrons (2 carbons = 8 electrons).
- Hydrogen (H): 1 valence electron (2 hydrogens = 2 electrons).
- Total = 10 valence electrons.
Drawing Skeleton:
- Arrange two carbons side by side and add one hydrogen to each.
Assign Electrons: Start with hydrogens (already satisfied having 2); assign leftover electrons to one carbon.
Sharing for Happiness: If carbon on one side does not have enough electrons after initial assignments, it may share electrons with surrounding atoms, resulting in double or triple bonds.

Counting Valence Electrons:
- Boron (B): 3 valence electrons.
- Hydrogen (H): 4 hydrogens = 4 electrons (+1 additional for the negative charge) = 8 total.
Skeleton Structure: Boron as the central atom surrounded by hydrogens.
Assign Electrons: Boron's 3 valence electrons are consumed in bonding, so additional hydrogens must be around to utilize available electrons.
Charge Representation: When complete, represent the charge outside the structure by placing brackets around the structure indicating its charge.

Reinforce concepts by practicing stepwise approaches and visualizing structures on different compounds, ensuring familiarity with the rules while recognizing exceptions.
Example Compound: Carbon Dioxide (CO2) should be approached through its electronic structure, central atom determination, valence assignment, and evaluation of the structure's completeness.
Final Notes: All compounds and reactions should be visualized using these methods, identifying keyatoms, distribution of electrons, and ensuring satisfaction according to established chemical rules.