Chemistry of Life: Organization of Matter

Basic Definitions and Concepts

Understanding the chemical basis of life is essential for studying anatomy and physiology. The following are foundational concepts:

• Matter: Anything that occupies space and has mass.

• Mass: The amount of matter in a substance; measured in kilograms or grams.

• Weight: The force exerted by gravity on an object’s mass.

• Element: A pure substance that cannot be broken down into simpler substances by ordinary chemical means. Each element is made of one type of atom.

Example: Oxygen (O) and Magnesium (Mg) are elements essential for life and are found on the periodic table.

The Periodic Table and Elements in the Human Body

• There are 112 known elements (92 natural, 20 synthetic).

• In the human body:

  • 96% of body mass comes from four elements: Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).

  • 3.6% comes from eight additional elements (e.g., calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium, iron).

  • 0.4% comes from 14 trace elements (e.g., iodine, zinc, copper, selenium).

Application: These elements are critical for physiological processes such as respiration, nerve conduction, and enzyme function.

Atomic Structure

Components of the Atom

Atoms are the smallest units of elements and the building blocks of matter.

• Nucleus: The central core of the atom, containing:

  • Protons (p+): Positively charged particles.

  • Neutrons (n0): Neutral particles (no charge).

• Electrons (e-): Negatively charged particles that revolve around the nucleus in defined energy shells.

• Neutral atoms: The number of protons equals the number of electrons, resulting in no net charge.

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

Atomic Number and Mass Number

Defining Atoms and Isotopes

• Atomic number: The number of protons in the nucleus of an atom. This 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).

• Isotopes have the same atomic number but different mass numbers.

Example: Carbon-12 and Carbon-13 are isotopes of carbon. Both have 6 protons, but Carbon-12 has 6 neutrons and Carbon-13 has 7 neutrons.

Additional info: Understanding atomic structure and isotopes is essential for topics such as medical imaging (radioisotopes) and metabolic processes in physiology.