An atom is the smallest unit of ordinary matter that forms a chemical element. Atoms are extremely small, typically around 100 picometers across. They consist of a small positively charged nucleus surrounded by a cloud of negatively charged electrons.
The concept of the atom dates back to ancient Greece, but our modern understanding began to take shape in the early 19th century with John Dalton's atomic theory. This theory proposed that all matter is composed of indivisible particles called atoms. In the 20th century, discoveries about the internal structure of atoms led to the development of quantum mechanics and a more complete atomic model.
Understanding the structure of atoms is essential to learning chemistry, as the properties and behavior of elements and compounds are determined by the interactions between atoms.
Atoms are composed of three primary subatomic particles: protons, neutrons, and electrons.
To be continued in the next lesson section...