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Atomic Structure. Building blocks of matter. Early Model of the Atom. Democritus- Greek Philosopher. Ideas based on observation alone. He thought atoms were tiny, indivisible, unchanging particles. He pictured them as a hard sphere.
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Atomic Structure Building blocks of matter
Early Model of the Atom • Democritus- Greek Philosopher. Ideas based on observation alone. He thought atoms were tiny, indivisible, unchanging particles. He pictured them as a hard sphere. • John Dalton(1766-1844) English school teacher. He worked with organic compounds. • All elements are composed of atoms. • Atoms of the same element are identical.
More Dalton • Atoms combine in whole number ratios. • In chemical reaction, atoms separate, join, or rearrange. • Atoms are very small, but have been observed using microscopes.
Structure of an atom • Subatomic particles- three particles make up the atom • Electron- (e) negative in charge, smallest of the particles, found in the electron cloud/shell • History- • JJ Thompson- worked with cathode ray tubes. Passed electricity through a gas. The gas glowed. Thompson called the particles in gas electrons, because it conducted electricity
More electron • Thompson then started using magnets. The positive pole attracted the beam of gas, the negative pole repulsed it. He knew opposites attract and predicted that the electron was negatively charged. • Crookes verified Thompson’s experiments • Millikan- Proved that electrons have mass.
Subatomic particles in nucleus • Proton- positive charge • Neutron- neutral or no charge • About the same size and mass • History- • Rutherford- Performed the “gold Foil” experiment. He shot alpha particles at gold foil. Alpha particles are positively charged. He expected them to go straight through the foil.
Protons and Neutrons • Instead they scattered and some bounced back. He concluded that there had to be a positive particle found in the center of the atom. • Chadwick- discovered the neutron
Models of the atom • Dalton’s
