1. Matter is made of atoms: It establishes that all substances, whether solid, liquid, or gas, are composed of tiny particles called atoms.
2. Atoms are indivisible: While atoms can be broken down into smaller particles (protons, neutrons, electrons), the theory originally stated that atoms themselves were the smallest unit of matter and could not be further divided.
3. Atoms of the same element are identical: It states that all atoms of a particular element have the same mass and chemical properties. For example, all gold atoms are identical.
4. Atoms of different elements are different: It clarifies that atoms of different elements have different masses and chemical properties. For instance, a carbon atom is different from an oxygen atom.
5. Atoms combine in whole-number ratios to form compounds: The theory explains that atoms of different elements combine in specific, fixed ratios to form molecules and compounds. For example, water is always formed by two hydrogen atoms and one oxygen atom (H₂O).
6. Chemical reactions involve the rearrangement of atoms: It explains that chemical reactions occur when atoms are rearranged, not destroyed or created. For example, in the combustion of wood, the atoms in the wood combine with oxygen atoms to form carbon dioxide and water.
7. Atoms have a nucleus containing protons and neutrons, surrounded by electrons: This is a modern addition to the theory, describing the internal structure of an atom.
In summary, atomic theory provides a framework for understanding the nature of matter and how substances are formed and interact. It has been refined and expanded over time, but its core principles remain fundamental to chemistry and physics.
