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

Chapter 2: The Chemistry of Life

Module 2.1: Atoms and Elements

This module introduces the foundational chemical concepts necessary for understanding human anatomy and physiology. It covers the structure of atoms, the nature of elements, and the significance of subatomic particles in biological systems.

Objectives

• Describe the structure of an atom and identify subatomic particles.

• Define the term element and list the major elements found in the human body.

• Explain atomic number, mass number, isotopes, and radioisotopes.

• Understand how isotopes are produced and their relevance in medicine.

Atomic Structure

An atom is the smallest unit of matter that retains the original properties of an element. Atoms are composed of even smaller structures called subatomic particles.

• Protons (p+): Located in the central core of the atom (atomic nucleus); positively charged.

• Neutrons (n0): Also in the atomic nucleus; slightly larger than protons; no charge (neutral).

• Electrons (e-): Located outside the atomic nucleus in electron shells; negatively charged.

Atoms are electrically neutral because the number of protons and electrons are equal, canceling each other's charge. The number of neutrons does not have to equal the number of protons.

Structure of a Representative Atom

• The nucleus contains protons and neutrons.

• Electrons occupy regions called electron shells around the nucleus.

• Each shell can hold a specific number of electrons (e.g., 1st shell: 2 electrons; 2nd shell: 8 electrons; 3rd shell: up to 18 electrons).

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Key Terms

• Element: A substance that cannot be broken down into simpler substances by chemical means. Each element is made of atoms with the same number of protons.

• Atomic Number: The number of protons in the atomic nucleus; defines the element.

• Mass Number: The sum of protons and neutrons in the nucleus.

• Isotope: Atoms of the same element with different numbers of neutrons (and thus different mass numbers).

• Radioisotope: An unstable isotope that releases radiation as it decays to a more stable form.

Major Elements of the Human Body

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

• Additional info: These elements make up over 96% of the human body's mass.

Subatomic Particle Comparison Table

Particle	Location	Charge	Relative Mass
Proton (p+)	Nucleus	+1	1
Neutron (n0)	Nucleus	0	1 (slightly more than proton)
Electron (e-)	Electron shells	-1	~1/1836 (much less than proton or neutron)

Important Equations

• Atomic Number: $\text{Atomic Number} = \text{Number of Protons}$

• Mass Number: $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

Example: Carbon-12 isotope: 6 protons + 6 neutrons = mass number 12.

Additional info: Understanding atomic structure is essential for grasping how elements interact in biological systems, form molecules, and participate in physiological processes.