Chapter 4 Elements and the Periodic Table
Section 1:Introduction to Atoms
How did atomic theory develop and change?
What is the modern model of the atom?
Chapter 4 Elements and the Periodic Table
Atomic Theory and Models
Dalton thought that atoms were like smooth, hard balls thatcould not be broken into smaller pieces.
Chapter 4 Elements and the Periodic Table
Atomic Theory and Models
Thomson suggested that atoms had negatively chargedelectrons embedded in a positive sphere.
Chapter 4 Elements and the Periodic Table
Rutherford’s Gold Foil Experiment
Rutherford was surprised that a few particles were deflectedstrongly. This led him to propose an atomic model with apositively charged nucleus.
Chapter 4 Elements and the Periodic Table
Later Atomic Models
Through the first part of the twentieth century, atomic modelscontinued to change.
Chapter 4 Elements and the Periodic Table
Modern Model of an Atom
This model of a carbon atom consists of positively chargedprotons and neutral neutrons in a nucleus that is surroundedby a cloud of negatively charged electrons.
Chapter 4 Elements and the Periodic Table
Particles in an Atom
An atom is composed of positively charged protons, neutralneutrons, and negatively charged electrons. Protons andneutrons are about equal in mass. An electron has about1/2,000 the mass of a proton or neutron.
Chapter 4 Elements and the Periodic Table
Isotopes
Atoms of all isotopes of carbon contain six protons and sixelectrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.
Chapter 4 Elements and the Periodic Table
More on Atomic Structure
Click the PHSchool.com button for an activityabout atomic structure.
Chapter 4 Elements and the Periodic Table
End of Section:Introduction to Atoms