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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 that
could not be broken into smaller pieces.
Chapter 4 Elements and the Periodic Table
Atomic Theory and Models
Thomson suggested that atoms had negatively charged
electrons 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 deflected
strongly. This led him to propose an atomic model with a
positively charged nucleus.
Chapter 4 Elements and the Periodic Table
Later Atomic Models
Through the first part of the twentieth century, atomic models
continued to change.
Chapter 4 Elements and the Periodic Table
Modern Model of an Atom
This model of a carbon atom consists of positively charged
protons and neutral neutrons in a nucleus that is surrounded
by 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, neutral
neutrons, and negatively charged electrons. Protons and
neutrons are about equal in mass. An electron has about
1/2,000 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 six
electrons, but they differ in their number of neutrons. Carbon12 is the most common isotope.
Chapter 4 Elements and the Periodic Table
More on Atomic Structure
Click the PHSchool.com button for an activity
about atomic structure.
Chapter 4 Elements and the Periodic Table
End of Section:
Introduction to Atoms