Chapter 2: The Chemical Context of Life

Chemical Connection to Biology

Biology is fundamentally the study of life, but all living organisms and their environments are governed by the laws of physics and chemistry. Understanding the chemical basis of life is essential for comprehending biological processes.

• Biology involves the study of living organisms and their interactions with the environment.

• All biological systems are subject to universal physical and chemical laws.

• Example: Ants use formic acid to defend themselves against predators and microbial parasites, illustrating the chemical strategies organisms use for survival.

Atoms, Elements, and Compounds

All matter is composed of atoms, which combine to form elements and compounds. The properties of compounds, such as formic acid, depend on the types of atoms present and how they are bonded together.

• Atom: The smallest unit of matter that retains the properties of an element.

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

• Compound: A substance consisting of two or more elements in a fixed ratio. Compounds have emergent properties different from their constituent elements.

• Example: Formic acid (HCOOH) is a compound made of hydrogen, carbon, and oxygen atoms joined by chemical bonds.

Atomic Structure and Properties

The identity and chemical behavior of an atom are determined by its subatomic particles and their arrangement.

• Protons: Positively charged particles in the nucleus; the number of protons defines the atomic number and the element's identity.

• Neutrons: Neutral particles in the nucleus; together with protons, they determine the atom's mass number.

• Electrons: Negatively charged particles that orbit the nucleus; their arrangement determines the atom's ability to form bonds.

• Electron Distribution: The arrangement of electrons in shells and orbitals influences chemical bonding and reactivity.

Properties of Compounds

The properties of a compound are determined by the types of atoms involved and the nature of their chemical bonds.

• Bonding: Atoms join together by forming chemical bonds, such as covalent or ionic bonds.

• Emergent Properties: Compounds often exhibit characteristics that are different from those of the individual elements that compose them.

• Example: Sodium (Na) is a reactive metal, and chlorine (Cl) is a poisonous gas, but together they form sodium chloride (NaCl), a stable edible salt.

Table: Major Elements in the Human Body

The following table summarizes the main elements found in the human body and their approximate percentage by mass (including water):

Additional info: Trace elements include boron, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium, silicon, tin, vanadium, and zinc.