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Section 1: Introduction to Atoms
How did atomic theory develop and change? What is the modern model of the atom?
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Atomic Theory and Models
Dalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.
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Atomic Theory and Models
Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere.
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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.
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Later Atomic Models Through the first part of the twentieth century, atomic models continued to change.
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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.
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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.
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Isotopes Atoms of all isotopes of carbon contain six protons and six electrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.
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More on Atomic Structure
Click the PHSchool.com button for an activity about atomic structure.
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End of Section: Introduction to Atoms
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