Atoms: The Smallest Unit of Matter

Definition and Hierarchy of Matter

All living and non-living things are composed of matter, which is anything that takes up space and has mass. Matter is made up of chemical elements, which are pure substances consisting of only one type of atom. Atoms are the smallest units of elements and, therefore, the smallest units of matter.

• Matter: Anything that occupies space and has mass (e.g., organisms, rocks, water).

• Chemical Element: A pure substance made of only one kind of atom (e.g., carbon, oxygen).

• Atom: The smallest unit of an element that retains its chemical properties.

Example: A flower is matter, composed of elements such as carbon and oxygen, which are made up of atoms.

Atomic Structure

Atoms are composed of three types of subatomic particles: protons, neutrons, and electrons. These particles differ in charge, mass, and location within the atom.

• Protons: Positively charged particles found in the nucleus; each has a mass of 1 atomic mass unit (AMU).

• Neutrons: Neutral particles (no charge) also located in the nucleus; each has a mass of 1 AMU.

• Electrons: Negatively charged particles that orbit the nucleus in energy shells; their mass is negligible compared to protons and neutrons.

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

Elements of Life

Only a small subset of all known elements are found in living organisms. The periodic table organizes these elements based on their chemical properties. The majority of living matter is composed of six elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS).

• Bulk Elements: Required in large amounts for life (e.g., CHNOPS).

• Trace Elements: Required in very small amounts but essential for life (e.g., iron, zinc).

Example: Carbon is a bulk element, while iodine is a trace element necessary for thyroid function.

Atomic Properties

Each atom of an element has unique properties, including atomic number, mass number, and atomic mass.

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

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

• Atomic Mass: The average total mass of all atoms of an element, accounting for isotopes.

Example: Carbon has an atomic number of 6 and a typical mass number of 12.

Summary Table: Subatomic Particles

Additional info: This table summarizes the basic properties of subatomic particles found in all atoms.