Chemical Level of Organization

Atoms

The atom is the smallest stable unit of matter and forms the foundation for all chemical processes in living organisms. Understanding atomic structure is essential for grasping the chemical basis of anatomy and physiology.

• Protons (p+): Positively charged particles found in the nucleus.

• Neutrons (n or n0): Electrically neutral particles also located in the nucleus.

• Electrons (e-): Negatively charged particles that orbit the nucleus in an electron cloud. Electrons are much smaller than protons or neutrons (about 1/1836 the mass).

Example: A hydrogen atom contains one proton and one electron.

Atomic Structure

Atoms can be subdivided into two main regions: the nucleus and the electron cloud.

• Nucleus: Located at the center of the atom, contains protons and may contain neutrons. The mass of the atom is mainly determined by the number of protons and neutrons.

• Electron Cloud: Created by the movement of electrons around the nucleus. Electrons occupy specific energy levels or shells.

Atomic Metrics and Elements

Atoms are characterized by specific numbers that define their identity and properties.

• Atomic Number: The total number of protons in an atom. Determines the element.

• Mass Number: The total number of protons and neutrons in an atom.

• Element: A pure substance composed only of atoms with the same atomic number. Elements are defined by the number of protons in their atoms.

Example: Hydrogen is the simplest element, with one proton and one electron.

Periodic Table of Elements

The periodic table organizes elements based on their atomic number and chemical properties. Each element is represented by a chemical symbol, which may be derived from English or other languages (e.g., O for oxygen, C for carbon, Na for sodium from Latin natrium).

• Elements in the Human Body: The body contains several principal elements (e.g., oxygen, carbon, hydrogen, nitrogen) and trace elements essential for physiological functions.

Atomic Interactions

Atoms interact by means of their electrons to produce larger, more complex structures such as molecules and compounds. These interactions are fundamental to the chemical processes that sustain life.

• Chemical Bonds: The force that holds atoms together in molecules and compounds.

• Electron Shells: Electrons occupy specific energy levels (shells) around the nucleus. The arrangement of electrons in these shells determines the chemical properties and reactivity of the atom.

Additional info: Atoms with full outer electron shells are chemically inert (noble gases), while those with unfilled shells are reactive and tend to form chemical bonds to achieve stability.