Organic Chemistry Lecture I Notes Review (CHEM-263-800)

Vocabulary flashcards covering key concepts from Organic Chemistry Lecture I notes, including structure, bonding, Lewis structures, isomerism, resonance, curved arrows, and molecular geometry.

Organic chemistry

A branch of chemistry that studies carbon-containing compounds and their reactions.

Alcohol

A class of organic compounds containing a hydroxyl (-OH) group.

Ethanol (CH3CH2OH)

A simple alcohol; used in beverages and as a building block in synthesis.

Carbon-containing molecules

Molecules that include carbon atoms, often with H, O, N, and other elements.

Common elements in organic compounds

Carbon (C), Hydrogen (H), and Oxygen (O) are frequently present in organic molecules.

Periodic group

A column in the periodic table; elements in the same group have similar valence and properties.

Valence electrons

Electrons in the outermost shell involved in bonding.

Carbon valence

Carbon has four valence electrons and typically forms four bonds.

Atomic orbitals

Regions where electrons are likely to be found; s orbitals are spherical, p orbitals are dumbbell-shaped with px, py, pz orientations.

Covalent bond

A bond formed by sharing a pair of electrons between two atoms.

Bond length

The distance between two bonded atoms; e.g., H–H bond length is 0.74 Å.

Molecule

A discrete group of atoms held together by covalent bonds.

Ionic bond

A bond formed by transfer of electrons from one atom to another (e.g., NaCl).

Lewis structure

A diagram showing atoms, valence electrons as dots, and bonds to satisfy octets.

Octet rule

Most second-row elements seek eight electrons around them, achieved via bonds and lone pairs.

Lone pair

A pair of valence electrons not involved in bonding.

Formal charge

Formal charge = valence electrons – (electrons in lone pairs) – (bonds); indicates electron distribution.

Isomer

Compounds with the same molecular formula but different connectivity or arrangement.

Constitutional isomer

Isomers with different bonding connectivities but the same formula.

Resonance

Delocalization of electrons across multiple structures; the real structure is a resonance hybrid.

Resonance structure

One possible Lewis structure showing a particular distribution of electrons.

Resonance hybrid

The actual structure, a blend of all resonance forms.

Major contributor

The resonance structure that contributes most to the hybrid (more bonds, fewer charges).

Curved arrows

Notation showing movement of electron pairs; starts at source (lone pair or pi bond) and ends at destination.

Rule 1 (curved arrows)

Do not break a sigma (single) bond when drawing resonance arrows.

Rule 2 (curved arrows)

Never exceed an octet for second-row elements when drawing arrows.

Curved arrow sources

Movable electrons are typically lone pairs or pi bonds.

VSEPR theory

Valence Shell Electron Pair Repulsion; predicts molecular geometry from electron-group repulsion.

Bond angle

The angle between adjacent bonds around a central atom (e.g., 180°, 120°, 109.5°).

Bond length trend

Across a period, bond lengths shorten with smaller atoms; down a group, bond lengths lengthen with larger atoms.

Molecular geometry (from VSEPR)

Shape around a central atom determined by the number of electron groups.

Linear geometry

Two groups around the central atom; bond angle ≈ 180°.

Trigonal planar geometry

Three groups around the central atom; bond angle ≈ 120°.

Tetrahedral geometry

Four groups around the central atom; bond angle ≈ 109.5°.

Methane geometry (CH4)

A tetrahedral arrangement with four equivalent C–H bonds and 109.5° angles.

Wedge/dash notation

3D depiction: solid line in plane, wedge toward viewer, dashed away from viewer.

Equivalent representations

Different valid drawings of the same molecule (e.g., CH4) that depict the same structure.

Ethylene (C2H4)

Molecule with a C=C double bond; example used to illustrate multiple bonds in Lewis structures.

Ammonia geometry (NH3)

Trigonal pyramidal geometry due to a lone pair repelling bonds, reducing bond angles from the ideal tetrahedral value.

Water geometry (H2O)

Bent geometry due to lone pair repulsion, resulting in bond angles smaller than 109.5°.