Nuclearity, changes

Actually, then, by our symbol jjU we are representing not an atom, but a nucleus. Our equation is written in terms of nuclei and particles associated with them. This nuclear equation tells us nothing about what compound ol uranium was bombarded with neutrons or what compound of barium is formed. We are summarizing only the nuclear changes. During the nuclear change there is much disruption of other atoms because of the tremendous amounts of energy liberated. We do not know in detail what happens but eventually we return to electrically neutral substances (chemical compounds) and the neutrons are consumed by other nuclei. 

If we wish to gain some idea of the alteration of mass in a nuclear change, we cannot use the fission reaction because the exact masses of the nuclei involved are not known. Let us look at another type of reaction of possible importance in the production of nuclear energy ... 

Let us do a little bookkeeping with the exact masses of these nuclei. Actually we will simplify a bit and use the exact masses of the atoms. This will make no difference. The masses of the atoms differ from the nuclear masses by the masses of the number of electrons in each atom. We have shown that electrons are conserved in nuclear changes. Exact masses of atoms (that is, exact masses of each isotopic species and not the chemical atomic weights shown on the inside back cover) are readily available. For our hydrogen-helium reaction we have... 

Ans. Nuclear equations are written to describe nuclear changes. However, since the correct number of electrons is available for the products, the equations can also be regarded as describing the reactions of complete atoms as well as just their nuclei. 

Transmutation A nuclear change that produces a new element from an old one. 

After a single dose of ethionine, triglycerides accumulate in the liver, the increase being detectable after four hours. After 24 hours, the accumulation of triglycerides is maximal, being 15 to 20 times the normal level. Initially, the fat droplets accumulate on the endoplasmic reticulum in periportal hepatocytes and then in more central areas of the liver. Some species develop hepatic necrosis as well as fatty liver, and nuclear changes and disruption of the endoplasmic reticulum may also be observed. 

All the chemical changes and many of the physical changes that we have studied so far involve alterations in the electronic structures of atoms. Electron-transfer reactions, emission and absorption spectra, and X rays result from the movement of electrons from one energy level to another. In all of these, the nuclei of the atoms remain unchanged, and different isotopes of the same element have the same chemical activity. Nuclear chemistry, or radioactivity, differs from other branches of chemistry in that the important changes occur in the nucleus. These nuclear changes also are represented by chemical equations. However, because the isotopes of the same element may, from a nuclear standpoint, be very different in reactivity, it is necessary that the equations show which isotopes are involved. 

They did not know that a nuclear change is necessary to convert one element into another element. 

Essential Question How is a nuclear change different from a chemical change ... 

To understand how radioactive substances can be used to determine the age of an object, it is necessary to understand radioactivity, the spontaneous or forced breakdown or rearrangement of the atomic nucleus with a release of radiation. We have discussed chemical changes in atoms in which outer electrons are shared, partially shared, or transferred, but the atomic nucleus remains intact. Here we are considering nuclear changes and the products produced, including radiation. We need a system of symbols to represent these nuclear changes. 

In a nuclear equation, mass numbers and number of protons add up to the same total on either side of the equation. Also, in addition to atomic nuclei particles (protons and neutrons), called nucleons, other particles are emitted or absorbed in the nuclear change. Some of these particles include the following ... 

There are many ways that nuclear changes occur. Emission of alpha particles is one result of nuclear decay ... 

Emission of beta particles can also result from a nuclear change ... 

Traditional chemical reactions occur as a result of the interaction between the valence electrons of atoms. In 1896, Henri Becquerel expanded the field of chemistry to include nuclear changes when he discovered that uranium emitted radiation. Soon after Becquerel s discovery, Marie Skladowska Curie began studying radioactivity and completed much pioneering work on nuclear changes. 

Swollen conidia were added to 25 mL of the medium for autopolyploidization in a 50-mL Erlenmeyer flask and incubated statically for 7 d at 28°C. The nuclear changes were then observed by nuclear staining using microscopes. 

The principle of small nuclear changes was given a theoretical basis by George Gamow. In 1928 he derived a successful theory of alpha decay, in which the nucleus is quantized and only small particles, such as protons or alpha particles, have a finite probability of tunneling through the nuclear barrier and escaping the nucleus. That... 

It is at this point, when the supposed transuranium elements were out of the picture, that the problem was finally solved. It happened because the chemists were now in familiar territory, with elements of known chemistry and tested radiochemistry. When their findings contradicted the physics assumption of small nuclear changes, the discrepancy was apparent and had to be resolved. It can be argued that their interdisciplinary collaboration functioned best just when Meitner was physically separated from her Berlin colleagues, and it is ironic that their separation produced a correspondence that demonstrates how effective this collaboration was. 

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