http://www.ck12.org Chapter 4. Atomic Structure
CHAPTER
4 Atomic Structure
Chapter Outline
4.1 Evolution of the Atomic Model
4.2 STRUCTURE OF THEATOM
4.3 ISOTOPES ANDATOMICMASS
4.4 REFERENCES
The concept of the atom was first proposed roughly two thousand years ago by the Greek philosopher Democritus.
He argued that matter was finite and comprised of particles that are indivisible. Like all the philosophers of his time,
Democritus based his argument on reason, not experimental data. In more recent years, the composition of matter
has been studied further, and only within the last century was it determined that the atom is indeed divisible. Today,
scientists believe that even some subatomic particles can theoretically be divided even further. The figure above
illustrates our modern model of the atom. At the center is a nucleus containing protons and neutrons. Around the
nucleus are much lighter particles called electrons. The atom is largely comprised of empty space. Can you think
of how we might go about studying the behavior of matter at the atomic and subatomic level? How do you suppose
we might study aspects of matter that cannot be directly observed? These are the questions that philosophers and
scientists have pondered for millennia. We will address some of these questions as we attempt to further understand
the particles that make up matter.
Iimage co pyright Anita Ponne, 2014 .www.shutterstock.com.U sed under license f rom Shutterstock.com.