THE STRUCTURE OF THE ATOM CHEMISTRY CHAPTER 4

SECTION 1: EARLY THEORIES OF MATTER

THE PHILOSOPHERS Several thousand years ago there were few tools for scientific exploration In these times curiosity and the power of the mind were the ways people found truth Scholarly thinkers called “philosophers” considered the many mysteries of life

EARLY THOUGHTS OF PHILOSOPHERS Many philosophers concluded that matter was composed of things such as earth, water, air, and fire It was also commonly accepted that matter could be endlessly divided into smaller pieces……….THAT IS ……UNTIL DEMOCRITUS CAME ALONG

DEMOCRITUS ( B.C.) First person to propose that matter was not infinitely divisible Believed that matter was made of tiny individual particles called “atomos” this is where the word atom is derived Although many of his ideas do not agree with modern atomic theory, his belief in the atom was amazingly ahead of his time.

REJECTION Philosophers criticized Democritus’s ideas asking him, “What holds atoms together?” Aristotle, the most influential Greek philosopher, rejected Democritus’s ideas. His influence was so great and the development of science was so primitive that his denial of the atom went largely unchallenged for 2000 years!!!!!!

JOHN DALTON ( ) Dalton revived and revised Democritus’s ideas based upon his research. 1. all matter is made of atoms 2. Atoms are indivisible and indestructible 3. Compounds are formed by a combination of 2 or more different kinds of atoms. 4. In chemical reactions, atoms are separated, combined, or rearranged.

DEFINING THE ATOM Atom- the smallest particle of an element that retains the properties of an element.

WHY IS DALTON SO IMPORTANT? He is the first person who used actual data to support the idea of the atom Not all of his theory was correct. We know now that atoms can be divided into subatomic particles (proton, neutron, electron)

SECTION 1 REVIEW 1. Why were Democritus’s ideas rejected by other philosophers? 2. Define the atom 3. Which parts of Dalton’s original atomic theory are now considered to be incorrect? 4. Democritus and Dalton both proposed the concept of atoms. Describe the method each used to reach that conclusion.

SECTION 2: THE NUCLEAR ATOM