The Chemistry of Life: Elements, Compounds, and Atomic Structure

The Chemistry of Life

Elements and Compounds

All living organisms are composed of matter, which is anything that occupies space and has mass. Understanding the nature of matter is fundamental to biology, as it underpins the structure and function of all biological molecules.

• Matter: Anything that takes up space and has mass.

• Element: A pure substance that cannot be broken down into other substances by chemical reactions. Examples include oxygen (O), carbon (C), and hydrogen (H).

• Compound: A substance consisting of two or more elements combined in a fixed ratio. Compounds have properties different from their constituent elements. For example, water (H2O) is a compound of hydrogen and oxygen.

• Example: Table salt (NaCl) is a compound formed from sodium (Na) and chlorine (Cl), both of which are elements.

The Elements of Life

Major and Trace Elements in the Human Body

Living organisms require various elements for survival, but only a few are present in large amounts. These are called major elements, while others are needed in minute quantities and are known as trace elements.

Element	Symbol	Percentage of Body Mass (including water)
Oxygen	O	65.0%
Carbon	C	18.5%
Hydrogen	H	9.5%
Nitrogen	N	3.3%
Calcium	Ca	1.5%
Phosphorus	P	1.0%
Potassium	K	0.4%
Sulfur	S	0.3%
Sodium	Na	0.2%
Chlorine	Cl	0.2%
Magnesium	Mg	0.1%

• Major elements (O, C, H, N) make up about 96.3% of body mass.

• Minor elements (Ca, P, K, S, Na, Cl, Mg) account for about 3.7%.

• Trace elements (such as B, Cr, Co, Cu, F, I, Fe, Mn, Mo, Se, Si, Sn, V, Zn) are required in amounts less than 0.01% of body mass but are essential for health.

• Example: Iron (Fe) is a trace element vital for oxygen transport in blood.

Additional info: The presence and balance of these elements are crucial for processes such as metabolism, nerve function, and structural integrity of cells.

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