chapter 1: atoms, orbitals, and electrons

What are valence electrons and why do they matter in organic chemistry?

Valence electrons are the electrons in the outermost shell of an atom. They determine how many bonds an atom can form and whether it prefers to gain, lose, or share electrons. In organic chemistry, bonding patterns (especially for C, N, O, halogens) depend almost entirely on valence electrons.

What rules govern electron configuration?

Electron configuration follows:

• Aufbau principle: electrons fill lowest-energy orbitals first

• Pauli exclusion principle: max 2 electrons per orbital with opposite spins

• Hund’s rule: electrons occupy degenerate orbitals singly before pairing

How do s and p orbitals differ?

• s orbitals: spherical, one per energy level

• p orbitals: dumbbell-shaped, three orientations (px, py, pz)

These shapes matter because bonding depends on orbital overlap.

What is electronegativity and why is it important?

Electronegativity measures how strongly an atom pulls electron density toward itself. Higher electronegativity means greater partial negative charge (δ−). Bond polarity, formal charge placement, inductive effects, and reactivity trends all rely on this concept.