write a visit to hospital
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Answers
The Early Atom
The Discovery of the Parts of the Atom
Modern scientific usage denotes the atom as composed of constituent particles: the electron, the proton and the neutron.
LEARNING OBJECTIVES
Discuss experiments that led to discovery of the electron and the nucleus
KEY TAKEAWAYS
Key Points
The British physicist J. J. Thomson performed experiments studying cathode rays and discovered that they were unique particles, later named electrons.
Rutherford proved that the hydrogen nucleus is present in other nuclei.
In 1932, James Chadwick showed that there were uncharged particles in the radiation he was using. These particles, later called neutrons, had a similar mass of the protons but did not have the same characteristics as protons.
Key Terms
scintillation: A flash of light produced in a transparent material by the passage of a particle.
alpha particle: A positively charged nucleus of a helium-4 atom (consisting of two protons and two neutrons), emitted as a consequence of radioactivity.
cathode: An electrode through which electric current flows out of a polarized electrical device.
Though originally viewed as a particle that cannot be cut into smaller particles, modern scientific usage denotes the atom as composed of various subatomic particles. The constituent particles of an atom (each discovered independently) are: the electron, the proton and the neutron. (The hydrogen-1 atom, however, has no neutrons, and a positive hydrogen ion has no electrons. )
image
Classical Atomic Model: Atomic model before the advent of Quantum Mechanics.
Electron
The German physicist Johann Wilhelm Hittorf undertook the study of electrical conductivity in rarefied gases. In 1869, he discovered a glow emitted from the cathode that increased in size with decrease in gas pressure. In 1896, the British physicist J. J. Thomson performed experiments demonstrating that cathode rays were unique particles, rather than waves, atoms or molecules, as was believed earlier. Thomson made good estimates of both the charge
e
and the mass
m
, finding that cathode ray particles (which he called “corpuscles”) had perhaps one thousandth the mass of hydrogen, the least massive ion known. He showed that their charge to mass ratio (e/m) was independent of cathode material. (Fig 1 shows a beam of deflected electrons. )
image
Electron Beam: A beam of electrons deflected in a circle by a magnetic field.
Proton
In 1917 (in experiments reported in 1919), Rutherford proved that the hydrogen nucleus is present in other nuclei, a result usually described as the discovery of the proton. Earlier, Rutherford learned to create hydrogen nuclei as a type of radiation produced as a yield of the impact of alpha particles on hydrogen gas; these nuclei were recognized by their unique penetration signature in air and their appearance in scintillation detectors. These experiments began when Rutherford noticed that when alpha particles were shot into air (mostly nitrogen), his scintillation detectors displayed the signatures of typical hydrogen nuclei as a product. After experimentation Rutherford traced the reaction to the nitrogen in air, and found that the effect was larger when alphas were produced into pure nitrogen gas. Rutherford determined that the only possible source of this hydrogen was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. One hydrogen nucleus was knocked off by the impact of the alpha particle, producing oxygen-17 in the process. This was the first reported nuclear reaction,
14
N
+
α
→
17
O
+
p
.
Neutron
In 1920, Ernest Rutherford conceived the possible existence of the neutron. In particular, Rutherford examined the disparity found between the atomic number of an atom and its atomic mass. His explanation for this was the existence of a neutrally charged particle within the atomic nucleus. He considered the neutron to be a neutral double consisting of an electron orbiting a proton. In 1932, James Chadwick showed uncharged particles in the radiation he used. These particles had a similar mass as protons, but did not have the same characteristics as protons. Chadwick followed some of the predictions of Rutherford, the first to work in this then unknown field.
Explanation:
As I entered the hospital, I saw people coming and going. I went to the enquiry office and enquired about the wards. First of all, I visited general ward where my friend was admitted. He was quite better now as his wounds had healed.