Ch. 4.2 Structure of the Ch. 4.2 Structure of the Nuclear AtomNuclear Atom

Subatomic ParticlesSubatomic Particles

Three types: electrons, protons, and Three types: electrons, protons, and neutrons.neutrons.

ElectronsElectrons discovered in 1897 by J.J. discovered in 1897 by J.J. Thomson.Thomson.

Negatively charged subatomic particles.Negatively charged subatomic particles.Discovered by passing electric current Discovered by passing electric current

through low-pressure gas chamber, with through low-pressure gas chamber, with metal plates (electrodes) at both ends.metal plates (electrodes) at both ends.

One electrode became positively charged, the One electrode became positively charged, the other negatively charged.other negatively charged.

Produced a glowing Produced a glowing cathode raycathode ray beam. beam. Beam could be deflected by magnets; Beam could be deflected by magnets;

conclusion was the beam was made of tiny conclusion was the beam was made of tiny charged particles, called charged particles, called electronselectrons..

Experiments confirmed charge-to-mass ratio of Experiments confirmed charge-to-mass ratio of electron; later confirmed by Millikan.electron; later confirmed by Millikan.

Mass is 1/1840Mass is 1/1840thth of a hydrogen atom. of a hydrogen atom.

Protons and NeutronsProtons and Neutrons

If atom loses electrons, what happens to If atom loses electrons, what happens to rest of the atom?rest of the atom?

Goldstein discovered oppositely moving Goldstein discovered oppositely moving beams in the cathode ray tube (canal rays) beams in the cathode ray tube (canal rays) were made of subatomic positively were made of subatomic positively charged particles….protons.charged particles….protons.

1932-James Chadwick confirmed 1932-James Chadwick confirmed existence of particle with no charge but existence of particle with no charge but mass similar to proton…the neutron. mass similar to proton…the neutron.

Rutheford’s Gold Foil ExperimentRutheford’s Gold Foil Experiment

In 1911, Rutherford directed a beam of In 1911, Rutherford directed a beam of alpha particles (positively charged helium alpha particles (positively charged helium nuclei) at a thin sheet of gold foil, nuclei) at a thin sheet of gold foil, expecting them to easily pass through with expecting them to easily pass through with slight deflection due to positive charges slight deflection due to positive charges spread throughout the atoms.spread throughout the atoms.

Most passed through Most passed through withoutwithout deflection. deflection. Some deflected at sharp angles, others Some deflected at sharp angles, others bounced straight back!bounced straight back!

Results suggested atom was mostly empty Results suggested atom was mostly empty space, with a small massive positively space, with a small massive positively charged nucleus.charged nucleus.

Rutherford model is called the Rutherford model is called the nuclear nuclear atomatom. Protons and neutrons in the . Protons and neutrons in the nucleus. Electrons distributed around the nucleus. Electrons distributed around the nucleus, making up almost all the atom’s nucleus, making up almost all the atom’s volume.volume.