Chapter 2: The Chemical Basis of Life – Elements, Atoms, and Compounds

Chapter 2: The Chemical Basis of Life

Big Ideas

• Elements, Atoms, and Compounds

• Chemical Bonds

• Water’s Life-Supporting Properties

Introduction

Chemicals are the raw materials that make up living organisms and their environments. Life’s chemistry is closely tied to water, as all living organisms require water and life first evolved in water.

• Chemicals compose our bodies, other organisms, and the physical environment.

• Water is essential for all living things.

Elements, Atoms, and Compounds

2.1 Organisms are Composed of Elements, in Combinations Called Compounds

Living organisms are made of matter, which is anything that occupies space and has mass (weight). Matter is composed of chemical elements.

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

• There are 92 elements in nature; only a few exist in pure form.

Elements in the Human Body

About 25 elements are essential for human life. Four elements make up about 96% of the weight of most living organisms:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

Trace elements are essential but only needed in minute quantities.

Table: Elements in the Human Body

Element	Symbol	Percentage of Body Weight
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%
Trace elements	Various	<0.01%

Compounds

• Compound: A substance consisting of two or more different elements in a fixed ratio.

• Compounds are more common than pure elements.

• Example: Sodium chloride (NaCl), or table salt, is a compound of equal parts sodium (Na) and chlorine (Cl).

2.2 CONNECTION: Trace Elements are Common Additives to Food and Water

Trace elements are required to prevent disease and are often added to food and water.

• Iron (Fe): Essential for oxygen transport in the body.

• Iodine (I): Prevents thyroid hormone deficiency; lack of iodine can result in goiter.

• Fluoride (F): Added to municipal water and dental products to help prevent tooth decay.

Food Additives

• Chemicals are added to food to preserve it, make it more nutritious, and improve appearance.

• Nutrition labels list the chemical elements and compounds present in foods and drinks.

Summary Table: Major and Trace Elements in Human Nutrition

Major Elements	Trace Elements
Oxygen, Carbon, Hydrogen, Nitrogen, Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, Magnesium	Iron, Iodine, Fluoride, Zinc, Copper, Selenium, Chromium, Manganese, Molybdenum, Cobalt

Key Terms and Definitions

• Element: Pure substance consisting of only one kind of atom.

• Compound: Substance formed from two or more elements in a fixed ratio.

• Trace Element: Element required by an organism in only minute quantities.

Applications and Examples

• Iron deficiency: Can lead to anemia due to reduced oxygen transport.

• Iodine deficiency: Can result in goiter, a swelling of the thyroid gland.

• Fluoride: Added to water supplies to reduce dental cavities.

Additional info: The notes cover foundational chemistry concepts essential for understanding biological molecules and processes, including the importance of water and trace elements in biology.