The Chemistry of Life: Atoms and Elements in Anatomy & Physiology

The Chemistry of Life

2.1 Atoms and Elements

This section introduces the foundational chemical concepts necessary for understanding biological processes in Anatomy & Physiology. It covers the structure of atoms, the nature of elements, and their relevance to the human body.

Definition and States of Matter

• Matter: Anything that has mass and occupies space. Matter exists in three states: solid, liquid, and gas.

• Chemistry: The study of matter and its interactions.

Atoms: The Basic Unit of Matter

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

• Atoms are composed of even smaller structures called subatomic particles:

  • Protons (p+): Positively charged, located in the nucleus.

  • Neutrons (n0): No charge (neutral), also in the nucleus.

  • Electrons (e-): Negatively charged, found in regions (shells) surrounding the nucleus.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

Atomic Structure

• Nucleus: The central core of the atom, containing protons and neutrons.

• Electron shells: Regions surrounding the nucleus where electrons are likely to be found. Each shell holds a specific number of electrons:

  • First shell: up to 2 electrons

  • Second shell: up to 8 electrons

  • Third shell: up to 8 electrons ("satisfied" with 8, though higher shells exist in larger atoms)

Elements and the Periodic Table

• Element: A substance that cannot be broken down into simpler substances by chemical means. Each element is defined by its number of protons.

• Atomic number: The number of protons in the nucleus of an atom; unique to each element.

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

• Isotopes: Atoms of the same element (same number of protons) but with different numbers of neutrons, resulting in different mass numbers.

• Radioisotopes: Unstable isotopes that release high energy or radiation as they decay to a more stable form.

Major Elements in the Human Body

• The human body is primarily composed of four major elements: Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).

• These elements are essential for the structure and function of biomolecules.

Example: Carbon Atom

• A typical carbon atom has 6 protons, 6 neutrons, and 6 electrons.

• Its atomic number is 6, and its mass number is 12.

Table: Comparison of Subatomic Particles

Particle	Charge	Location	Relative Mass
Proton (p+)	+1	Nucleus	1
Neutron (n0)	0	Nucleus	1
Electron (e-)	-1	Electron shells	~1/1840

Key Terms and Definitions

• Atom: Smallest unit of an element, composed of protons, neutrons, and electrons.

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

• Isotope: Atoms of the same element with different numbers of neutrons.

• Radioisotope: An unstable isotope that emits radiation.

Applications in Anatomy & Physiology

• Radioisotopes are used in medical imaging and cancer treatment.

• Understanding atomic structure is essential for grasping how molecules interact in biological systems.

Additional info: The periodic table organizes elements by increasing atomic number and groups elements with similar chemical properties together. In human physiology, trace elements (such as iron, iodine, and zinc) are also vital for specific biochemical functions.