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Organic chemistry is the study of carbon-containing compounds and their reactions. Carbon's ability to form four covalent bonds allows it to build chains, rings, and branched architectures of enormous structural diversity. The concept of hybridization (sp3, sp2, sp) explains carbon's geometry in different bonding environments and governs bond angles, lengths, and strengths. Understanding how electrons are distributed in organic molecules — through bonding, lone pairs, and resonance — is the foundation for predicting chemical reactivity.
Build physical or digital molecular models of methane, ethylene, and acetylene to internalize tetrahedral, trigonal planar, and linear geometries. Practice converting between Lewis structures and skeletal (line-bond) notation until line structures feel natural. Revisit VSEPR and resonance before moving forward.
Organic chemistry begins with carbon, and the first question is: why carbon? The answer lies in its bonding behavior. From your study of covalent bonding and Lewis structures, you know that carbon has four valence electrons and forms exactly four covalent bonds. That number — four — is what makes carbon special. With four bonding slots, a carbon atom can simultaneously bond to other carbons (forming chains and rings) and to hydrogen, oxygen, nitrogen, or halogens. The result is an enormous structural diversity: millions of distinct stable molecules built from a small set of elements.
Hybridization explains the geometry of that bonding. When carbon forms four single bonds (as in methane, CH₄), it uses sp3 hybridization — the s orbital and all three p orbitals mix to form four equivalent hybrid orbitals pointing to the corners of a tetrahedron, 109.5° apart. When carbon forms a double bond (as in ethylene, C₂H₄), it uses sp2 hybridization — mixing with only two p orbitals gives three hybrid orbitals in a flat trigonal planar arrangement (~120°), while the remaining unhybridized p orbital overlaps sideways with the adjacent carbon's p orbital to form the pi bond. Triple bonds (as in acetylene, C₂H₂) use sp hybridization, leaving two unhybridized p orbitals for two pi bonds and producing a linear geometry. Each hybridization type has characteristic bond angles, bond lengths, and chemical reactivity — understanding which type is present in a molecule tells you a great deal about how it will behave.
Skeletal structures are the notation system organic chemistry uses to represent molecules concisely. Instead of drawing every carbon and hydrogen explicitly, skeletal notation draws only the carbon skeleton (as lines and vertices) and any non-hydrogen atoms explicitly. The implicit rule is: every vertex and line-end is a carbon, and every carbon has enough hydrogens to reach exactly four bonds. Once this rule is second nature, you can read a skeletal structure as quickly as reading text — practice converting between Lewis structures and skeletal notation until this fluency feels automatic.
The distribution of electrons in an organic molecule — through bonding orbitals, lone pairs, and resonance — is the foundation for everything else in organic chemistry. Electrons are where the chemistry happens: electron-rich regions attract electrophiles (electron-seekers), and electron-poor regions attract nucleophiles (electron-donors). Before you can predict whether a reaction will happen, or where on a molecule it will occur, you need to understand where the electrons are and how stable they are. Resonance, which you may have seen briefly in general chemistry, describes molecules where electrons are delocalized across multiple bonds — and those molecules are more stable and react differently than their Lewis structures suggest.
One conceptual correction worth making now: "organic" in chemistry is not a synonym for "natural," "healthy," or "safe." Organic chemistry is simply the chemistry of carbon-based compounds. Many synthetic drugs, plastics, and industrial chemicals are organic. Many naturally occurring compounds (like cyanide, or the toxins in certain plants) are also organic. Conversely, "inorganic" molecules like water and ammonia are not organic because they don't have carbon as a backbone. Keeping this definition precise will prevent confusion as the course deepens.