Atomic Structure:

• Atoms are the basic units of matter, defined by atomic number (number of protons) and mass number (protons + neutrons).

• Isotopes have the same atomic number but different mass numbers due to varying neutrons.

• Ions are atoms with unequal numbers of protons and electrons: cations (positive) and anions (negative).

Electron Configuration:

• Electrons fill orbitals according to the Aufbau Principle (lowest energy first), Pauli Exclusion Principle (no two electrons in the same orbital have the same spin), and Hund's Rule (one electron per orbital before pairing).

• Condensed electron configurations use the previous noble gas as a starting point.

• Example: Phosphorus (Z = 15) electron configuration.

Electronegativity:

• Electronegativity is an element's ability to attract electrons in a bond.

• It increases from left to right across a period and up a group in the periodic table.

Octet Rule:

• Main group elements tend to achieve 8 valence electrons (octet) through bonding.

• Valence electrons are those in the outermost shell; shared electrons are those involved in bonds.

Formal Charge:

• Used to check the correctness of Lewis structures.

• Formal Charge=Valence Electrons−(Nonbonding Electrons+Bonding Electrons/2)

• The sum of formal charges equals the overall charge of the molecule or ion.

Lewis Dot Structures:

• Show valence electrons and bonding in molecules.

• Steps: count valence electrons, arrange atoms, connect with bonds, complete octets, assign remaining electrons, check formal charges.

Resonance Structures:

• Some molecules have multiple valid Lewis structures (resonance) differing only in electron placement.

• Resonance hybrids represent the true structure, with double-headed arrows between forms.

Hybridization:

• Describes mixing of atomic orbitals to form new hybrid orbitals for bonding.

• Electron group geometry determines hybridization:

  • 2 groups: linear (sp)

  • 3 groups: trigonal planar (sp2)

  • 4 groups: tetrahedral (sp3)

Molecular Polarity:

• Polarity depends on molecular shape and distribution of electronegative atoms.

• Nonpolar molecules have symmetric charge distribution; polar molecules have asymmetric distribution.

Functional Groups:

• Specific groups of atoms within molecules responsible for characteristic chemical reactions (e.g., alcohols, amines, carbonyls).

Organic Chemistry Basics:

• Organic molecules contain carbon and hydrogen, sometimes with other elements.

• Hydrocarbons are molecules with only carbon and hydrogen.