Carbon & the Molecular Diversity of Life – Study Notes (General Biology, Chapter 3)

Carbon & the Molecular Diversity of Life

Introduction

Carbon is a fundamental element in biological molecules, enabling the vast diversity of life due to its unique bonding properties. This chapter explores how carbon atoms form complex molecules, the structural variety of organic compounds, and the significance of hydrocarbons in biological systems.

Formation of Bonds with Carbon

Atomic Structure and Bonding

Carbon atoms have the ability to form stable covalent bonds with up to four other atoms, making them central to organic chemistry.

• Electron Configuration: Carbon has 6 electrons: 2 in the first energy level and 4 in the second (valence shell).

• Bonding Behavior: Carbon shares its 4 valence electrons to complete its shell with 8 electrons, forming covalent bonds.

• Molecular Complexity: Each carbon atom can branch in four directions, allowing the formation of large, complex molecules.

• Example: Methane (CH4) is a simple molecule where carbon bonds to four hydrogen atoms.

Molecular Geometry of Carbon Compounds

Shapes and Types of Bonds

The geometry of carbon-containing molecules depends on the types of bonds formed and the arrangement of atoms.

Compound	Molecular Formula	Structural Formula	Geometry	Bond Type
Methane	CH4	H–C–H (tetrahedral)	Tetrahedron	Single bonds
Ethylene	C2H4	H2C=CH2	Planar	Double bond
Acetylene	C2H2	HC≡CH	Linear	Triple bond

• Single Bonds: Allow free rotation and tetrahedral geometry.

• Double Bonds: Restrict rotation, resulting in planar geometry.

• Triple Bonds: Create linear geometry.

Molecular Diversity Arising from Variation in Carbon Skeletons

Structural Variety in Organic Molecules

Carbon chains form the backbone of most organic molecules, and their diversity is key to the complexity of life.

• Skeleton Variation: Carbon skeletons can be straight, branched, or arranged in rings.

• Bond Variation: Some skeletons include double or triple bonds, affecting molecular properties.

• Hydrocarbons: Organic molecules consisting only of carbon and hydrogen.

• Properties of Hydrocarbons: They are hydrophobic (insoluble in water), nonpolar, and release large amounts of energy when oxidized.

• Example: Petroleum is rich in hydrocarbons and serves as a major energy source.

Additional info: Hydrocarbons are important in biological membranes and energy storage due to their nonpolar nature and high energy content.