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Chemistry 4.2. Structure of the Nuclear Atom. 4.2. Cathode-ray tubes are found in TVs, computer monitors, and many other devices with electronic displays. 4.2. Subatomic Particles. Subatomic Particles What are three kinds of subatomic particles?. 4.2. Subatomic Particles.
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Structure of the Nuclear Atom 4.2 • Cathode-ray tubes are found in TVs, computer monitors, and many other devices with electronic displays.
4.2 Subatomic Particles • Subatomic Particles • What are three kinds of subatomic particles?
4.2 Subatomic Particles • Three kinds of subatomic particles are electrons, protons, and neutrons.
Cathode Ray Tube • William Crookes used a glass tube that was used to study the relationship between mass and charge. • Metal electrodes were placed in each end of the tube. The metal plate that was connected to the negative terminal of the battery was called the cathode. Electrode connected to the positive terminal was called the Anode.
4.2 Subatomic Particles • Electrons • In 1897, the English physicist J. J. Thomson (1856–1940) discovered the electron. Electrons are negatively charged subatomic particles.
In the mid-nineteenth century, Julius Plücker investigated the light emitted in discharge tubes (Crookes tubes) and the influence of magnetic fields on the glow. • Later, in 1869, Johann Wilhelm Hittorf studied discharge tubes with energy rays extending from a negative electrode, the cathode. • These rays produced a fluorescence when they hit a tube's glass walls, and when interrupted by a solid object they cast a shadow.
4.2 Subatomic Particles • Thomson performed experiments that involved passing electric current through gases at low pressure. The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode.
4.2 Subatomic Particles • Cathode Ray Tube
In a cathode-ray tube, electrons travel as a ray from the cathode (-) to the anode (+). A television tube is a specialized type of cathode-ray tube.
Thomson examined two ways that a cathode ray can be deflected: a) by using a magnet, and b) by using electrically charged plates. Inferring If a cathode ray is attracted to a positively charged plate, what can you infer about the charge of the particles that make up the cathode ray?
4.2 Subatomic Particles • A cathode ray is deflected by a magnet.
4.2 Subatomic Particles • A cathode ray is deflected by electrically charged plates.
4.2 Subatomic Particles • Thomson concluded that a cathode ray is a stream of electrons. Electrons are parts of the atoms of all elements.
4.2 Subatomic Particles • Protons and Neutrons • In 1886, Eugen Goldstein (1850–1930) observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles. • Such positively charged subatomic particles are called protons.
Electron in bottom Protons are red • (Green)
4.2 Subatomic Particles • In 1932, the English physicist James Chadwick (1891–1974) confirmed the existence of yet another subatomic particle: the neutron. • He work under Rutherford research. • Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton.
He devised a simple apparatus that consisted of a cylinder containing a polonium source and beryllium target. • The resulting radiation could then be directed a material such as paraffin wax and the particles displaced, which were protons, would go into a small ionisation chamber where they could be detected with an oscilloscope.
4.2 Subatomic Particles • Table 4.1 summarizes the properties of electrons, protons, and neutrons.
4.2 The Atomic Nucleus • The Atomic Nucleus • How can you describe the structure of the nuclear atom?
4.2 The Atomic Nucleus • J.J. Thompson and others supposed the atom was filled with positively charged material and the electrons were evenly distributed throughout. • This model of the atom turned out to be short-lived, however, due to the work of Ernest Rutherford (1871–1937).
4.2 The Atomic Nucleus • Ernest Rutherford’s Portrait • Born in New Zealand, Nobel Prize 1908
4.2 The Atomic Nucleus • Rutherford’s Gold-Foil Experiment • In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil.
4.2 The Atomic Nucleus • Rutherford’s Gold-Foil Experiment
Gold Foil Experiment yield that an atomic nucleus is present. • Most of the particles passed through but some were deflect. • He measured the angle of deflection. • The experiment indicated the atom was made mostly of space. The nucleus is were the mass and positive charge is concentrated. Nucleus deflected the particles.
4.2 The Atomic Nucleus • Alpha particles scatter from the gold foil.
4.2 The Atomic Nucleus • The Rutherford Atomic Model • Rutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus. • The nucleus is the tiny central core of an atom and is composed of protons and neutrons.
4.2 The Atomic Nucleus • In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom. • Proton and neutrons 99% of mass • Electron make up 99% of volume
4.2 Section Quiz • 4.2.
4.2 Section Quiz • 1. Which of the following is NOT an example of a subatomic particle? • proton • molecule • electron • neutron
4.2 Section Quiz • 2. The nucleus of an atom consists of • electrons only. • protons only. • protons and neutrons. • electrons and neutrons.
4.2 Section Quiz • 3. Most of the volume of the atom is occupied by the • electrons. • neutrons. • protons and neutrons. • protons.
