Carbon and Molecular Diversity of Life — Vocabulary Flashcards

Page 2: Carbon is the Backbone of Life

Elements and valence in biological molecules:
- Hydrogen (valence = 1)
- Oxygen (valence = 2)
- Nitrogen (valence = 3)
- Carbon (valence = 4)
Formal statement: Organic compounds are carbon-based.
Key takeaway: Carbon atoms form the framework for life’s molecules due to their tetravalence and bonding versatility.
Valence details (as explicit values):
- ext{valence}(\mathrm{H}) = 1
- ext{valence}(\mathrm{O}) = 2
- \text{valence}(\mathrm{N}) = 3
- \text{valence}(\mathrm{C}) = 4

Carbon bonding capabilities:
- Carbon (valence = 4) can form covalent bonds with up to four other atoms at the same time.
- Usually, the major bonding partners are the elements H, O, N, or C (the "Big Four").
- Carbon can form single, double, or triple bonds (triple bonds are rare in simple organic molecules).
Representations of molecules:
- Molecular formula
- Structural formula
- Ball-and-stick model
- Space-filling model
Examples (illustrative formulas and structures):
- Methane: \mathrm{CH_4}
- Structural depiction: H–C–H with the remaining hydrogens arranged around the carbon (tetrahedral in 3D, but shown simplistically as H-C-H with other H atoms attached).
- Ethane: \mathrm{C2H6}
- Structural depiction: H–C–C–H with hydrogens around each carbon (simplified as H–C–C–H with additional H atoms not drawn in the shorthand).
- Ethene (Ethylene): \mathrm{C2H4}
- Structural depiction: C=C with hydrogens attached to the carbons (H around the C=C framework).

Definition:
- A carbon skeleton represents the backbone of an organic molecule, formed by a chain of carbon atoms connected to each other via covalent bonds.
Characteristics of carbon skeletons:
- The skeleton can be straight, branched, or arranged in rings.
- The length of the skeleton can vary; more carbons add to chain length.
- Carbon skeletons may include double bonds within them.
- Skeletons may be branched or unbranched.
- Double bonds can occur at different locations along the chain.
- Some carbon skeletons form rings (cyclic structures).
- Abbreviated structural formulas omit corner carbons and the hydrogens attached to them.
Examples (skeletons and formulas):
- Ethane skeleton (simplified): H–C–C–H with surrounding H atoms; single bonds connect carbons.
- Propane: \mathrm{C3H8}
- Butane: \mathrm{C4H{10}}
- Isobutane: \mathrm{C4H{10}} (branched isomer of butane)
- Cyclohexane: \mathrm{C6H{12}} (ring structure)
- Benzene: \mathrm{C6H6} (aromatic ring with alternating double bonds, though often represented with a resonance structure)
- 1-Butene and 2-Butene: \mathrm{C4H8} (double bond location differs between isomers)
Key ideas:
- Single bonds vs double bonds affect shape and reactivity.
- Rings introduce cyclic geometry and can stabilize certain conformations.

Central concept:
- The carbon skeleton structure models the backbone of an organic molecule as a chain of carbon atoms connected by covalent bonds.
- Examples show various arrangements: linear chains, branched chains, and ring systems.
Specific notes (as depicted):
- Propane representation: H–C–C–C–H with surrounding hydrogens to fill valence.
- Propane (summary): the backbone is a straight chain of three carbon atoms, with hydrogens attached to satisfy valence.
- The phrase: "✰ Carbon skeleton represents the backbone of an organic molecule, formed by a chain of carbon atoms connected to each other via covalent bonds. The carbon skeleton can be straight, branched, or arranged in rings, and determines the overall shape and properties of the molecule" summarizes the role of the skeleton in determining molecular geometry and properties.
Takeaway:
- The arrangement of carbon atoms (length, branching, ring formation, and presence/location of multiple bonds) governs the molecule’s three-dimensional shape and its chemical and physical properties.