Fundamental Atomic and Molecular Properties

Atomic Structure and Periodic Trends

Understanding atomic properties is essential for predicting chemical behavior and bonding in organic molecules.

• Ionization Energy: The energy required to remove an electron from an atom in the gas phase. Higher ionization energy indicates a stronger hold on electrons.

• Atomic Radius: The distance from the nucleus to the outermost electron shell. Atomic radius decreases across a period and increases down a group.

• Electronegativity: The tendency of an atom to attract electrons in a chemical bond. Fluorine is the most electronegative element.

• Electron Configuration: The arrangement of electrons in an atom's orbitals. Example: Carbon:

Chemical Bonding and Molecular Structure

Types of Chemical Bonds

Chemical bonds form through the sharing or transfer of electrons between atoms.

• Ionic Bond: Formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions.

• Polar Covalent Bond: Electrons are shared unequally due to differences in electronegativity.

• Nonpolar Covalent Bond: Electrons are shared equally between atoms of similar electronegativity.

Bond Polarity and Dipoles

• Bond Dipole: A separation of charge in a bond due to differences in electronegativity.

• Dipole Moment: A measure of the overall polarity of a molecule. Calculated as where is the charge and is the distance.

Lewis Structures and Formal Charge

• Lewis Structure: A diagram showing the arrangement of atoms and electrons in a molecule.

• Dot Diagram: Another term for Lewis structure, emphasizing valence electrons.

• Octet Exceptions: Molecules or ions where atoms do not follow the octet rule (e.g., BF3, SF6).

• Formal Charge: Calculated as:

Resonance and Isomerism

• Resonance: Delocalization of electrons in molecules with multiple valid Lewis structures. Resonance stabilizes molecules.

• Constitutional Isomer: Compounds with the same molecular formula but different connectivity.

• Conformational Isomer: Isomers differing by rotation around single bonds.

• Cis/Trans Isomer: Stereoisomers with different spatial arrangements around a double bond or ring.

Bonding Theories and Molecular Orbitals

Valence Bond Theory and Hybridization

Valence Bond Theory explains how atomic orbitals combine to form chemical bonds.

• Hybridized Orbital: Orbitals formed by mixing atomic orbitals (e.g., sp3, sp2, sp).

• Unhybridized Orbital: Atomic orbitals not involved in hybridization (e.g., p orbitals in pi bonds).

• Sigma () Bond: A single covalent bond formed by head-on overlap of orbitals.

• Pi () Bond: A covalent bond formed by side-to-side overlap of unhybridized p orbitals.

• Bond Length: The distance between nuclei of bonded atoms.

• Bond Strength: The energy required to break a bond.

Acids, Bases, and pKa

Acid-Base Theories

• Brønsted–Lowry Acid: Proton (H+) donor.

• Brønsted–Lowry Base: Proton acceptor.

• Arrhenius Acid: Produces H+ in water.

• Arrhenius Base: Produces OH- in water.

• Lewis Acid: Electron pair acceptor.

• Lewis Base: Electron pair donor.

• Amphiprotic: Can act as both acid and base (e.g., water).

• Conjugate Acid/Base: Species formed after an acid donates or a base accepts a proton.

• pKa: ; lower pKa means stronger acid.

Stereochemistry and Isomerism

Chirality and Stereoisomers

• Chiral Center: A carbon atom bonded to four different groups.

• Enantiomer: Non-superimposable mirror image isomers.

• Racemic Mixture: Equal amounts of two enantiomers; optically inactive.

• Enantiomeric Excess:

• Optical Activity: Ability to rotate plane-polarized light; measured as specific rotation.

• Levotatory (–): Rotates light to the left.

• Dextrorotatory (+): Rotates light to the right.

• Stereogenic Center: An atom at which the interchange of two groups produces a stereoisomer.

• Fischer Projection: 2D representation of 3D molecules, especially carbohydrates.

• Haworth Projection: Cyclic representation of sugars.

Physical Properties and Intermolecular Forces

Intermolecular Forces

• Hydrophilic: Water-attracting (polar).

• Hydrophobic: Water-repelling (nonpolar).

• Delocalized Electrons: Electrons spread over several atoms, as in resonance.

• Conjugated System: Alternating single and multiple bonds allowing electron delocalization.

Physical Properties

• Melting Point: Temperature at which a solid becomes a liquid.

• Boiling Point: Temperature at which a liquid becomes a gas.

• Water Solubility: Ability of a substance to dissolve in water; influenced by polarity and hydrogen bonding.

Alkanes and Cycloalkanes

Nomenclature and Structure

• Alkane Formula: for straight-chain alkanes.

• Constitutional Isomers: Different connectivity, same formula.

• IUPAC Naming: Systematic method for naming organic compounds.

• Common Names: Used for simple alkanes (e.g., methane, ethane, propane, butane).

• Branched Alkanes: Recognize and name iso-, sec-, tert-butyl groups.

Cyclohexane Conformations

• Chair Conformation: Most stable conformation of cyclohexane, minimizing torsional and steric strain.

• Axial/Equatorial Positions: Axial are perpendicular to the ring; equatorial are around the ring's equator.

Combustion and Redox Reactions

• Combustion of Alkanes:

• Oxidation: Increase in C–O bonds or decrease in C–H bonds.

• Reduction: Increase in C–H bonds or decrease in C–O bonds.

Organic Reaction Mechanisms

Mechanisms and Arrow-Pushing

• Mechanism: Stepwise description of how reactants convert to products, showing electron movement with arrows.

• Nucleophile: Electron-rich species that donates electrons.

• Electrophile: Electron-poor species that accepts electrons.

• Arrow-Pushing: Curved arrows show movement of electron pairs during reactions.

Summary Table: Key Acid-Base Concepts

Essential Skills for Organic Chemistry

Skills Checklist

• Draw resonance structures with electron movement arrows

• Draw and identify isomers (constitutional, conformational, stereoisomers)

• Determine molecular dipoles and polarity

• Assign formal charges and hybridization

• Identify intermolecular forces

• Recognize nucleophiles and electrophiles

• Classify acids and bases (Brønsted–Lowry, Lewis)

• Predict reaction direction using pKa values

• Draw conjugate acids and bases

• Compare acid/base strength using pKa and reasoning

• Draw acid-base reaction mechanisms

• Identify functional groups

• Compare water solubility, melting, and boiling points

• Determine alkane formulas and draw isomers

• Name alkanes using IUPAC and common systems

• Draw cyclohexane chair conformations

• Write balanced combustion equations for alkanes

• Identify oxidation/reduction reactions

• Identify and assign configurations to chiral centers

• Determine relationships between molecules (isomers, etc.)

• Assess optical activity and enantiomeric excess

Additional info: Some terms and skills (e.g., "leveling effect," "mechanism arrows," "bicyclic," "symmetry") are inferred to be relevant to introductory organic chemistry and are included for completeness.