Chapter 2: The Chemical Context of Life

Emergent Properties of Compounds

Compounds are substances formed when two or more elements combine in fixed ratios. The properties of a compound can be very different from those of its constituent elements, a phenomenon known as emergent properties.

• Definition: Emergent properties are characteristics that arise when individual components interact, producing effects not present in the individual elements.

• Example: Sodium (Na) is a highly reactive metal, and chlorine (Cl2) is a poisonous gas. When combined, they form sodium chloride (NaCl), or table salt, which is safe to eat and essential for life.

Elements in the Human Body

Living organisms are composed of a limited number of chemical elements. The human body is primarily made up of a few major elements, with others present in smaller or trace amounts.

• Element: A substance that cannot be broken down into other substances by chemical means.

• Major Elements: Four elements make up about 96% of the human body: Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).

• Minor Elements: Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium make up most of the remaining 4%.

• Trace Elements: Elements required in very small amounts (less than 0.01% of body mass), such as iron, iodine, and zinc, are essential for proper physiological function.

Application: Deficiencies in trace elements can lead to health problems. For example, lack of iodine can cause thyroid gland issues.