Chapter 4: Carbon and the Molecular Diversity of Life

Concept 4.1: Organic Chemistry and Carbon Compounds

Organic chemistry is the branch of science that studies compounds containing carbon. Carbon is fundamental to life, as living organisms are primarily composed of carbon-based compounds. The versatility of carbon allows for the formation of a vast array of organic molecules, ranging from simple to highly complex structures.

• Carbon: The Backbone of Life - Most living organisms consist mainly of carbon-based compounds.

• Organic Chemistry - The study of compounds that contain carbon, regardless of their origin.

• Organic Compounds - These range from simple molecules (e.g., methane) to colossal ones (e.g., DNA).

• Major Elements in Living Matter - The elements C, H, O, N, S, and P are present in similar proportions across different organisms.

• Versatility of Carbon - Carbon’s ability to form four covalent bonds enables the construction of an immense variety of organic molecules, contributing to the diversity of life.

Concept 4.2: Carbon Bonding and Molecular Diversity

Carbon atoms can form diverse molecules by bonding to four other atoms. The electron configuration of carbon determines the number and types of bonds it can form, allowing for the creation of large and complex molecules essential for life.

• Four Valence Electrons - Carbon has four electrons available for bonding, enabling it to form four covalent bonds with other atoms.

• Tetrahedral Shape - In molecules where each carbon is bonded to four other atoms, the resulting geometry is tetrahedral.

• Double Bonds - When two carbon atoms are joined by a double bond, the atoms attached to them lie in the same plane.

• Covalent Compatibility - Carbon’s electron configuration allows it to bond with many elements, especially hydrogen, oxygen, and nitrogen.

Table: Examples of Simple Carbon Compounds

Valences of Major Elements in Organic Molecules

The valence (number of bonds formed) of carbon and its frequent partners is crucial for the structure of biological molecules.

• Hydrogen (valence = 1): Forms one bond (e.g., H–).

• Oxygen (valence = 2): Forms two bonds (e.g., –O–).

• Nitrogen (valence = 3): Forms three bonds (e.g., –N=).

• Carbon (valence = 4): Forms four bonds (e.g., –C–).

These valences are the building code for the architecture of living molecules.

Additional info:

• Organic molecules can vary in length, branching, and the presence of rings, contributing to molecular diversity.

• Hydrocarbons are organic molecules consisting only of carbon and hydrogen, and they can release significant energy during reactions.