http://www.ck12.org Chapter 4. Atomic Structure
CHAPTER
4 Atomic Structure
Chapter Outline
4.1 Atoms
4.2 THENUCLEARMODEL OF THEATOM
4.3 ISOTOPES ANDATOMICMASS
4.4 REFERENCES
Have you ever tried to observe or study something that you could not see? Scientists are faced with this problem
each and every day. Geologists must attempt to describe things such as the interior of Earth or the way in which
mountains and deserts came to be. Astronomers attempt to map the outer reaches of the Universe. Chemists and
physicists across the centuries have been concerned with the smallest particles that make up each and every object in
our natural world. Of course, that is the atom. How do scientists study things they can’t see? They make models. A
scientific model is a tool constructed by the scientist based on all the known experimental evidence about a particular
thing, such as an atom. The picture above is an artistic look at one model of the atom, showing the electrons in orbit
around the central nucleus. As time goes by and more experiments are performed, models evolve and change to
account for new understanding. In this chapter, you will begin to learn about how the model of the atom was initially
developed and how it has changed over time into what we now have come to accept as the modern model of the
atom.
Image co pyright Jez per, 2014 .www.shutterstock.com.U sed under license f rom Shutterstock.com.