Subatomic particles, importance

The uncertainty principle has negligible practical consequences for macroscopic objects, but it is of profound importance for subatomic particles such as the electrons in atoms and for a scientific understanding of the nature of the world. 

The de Broglie equation predicts that eveiy particle has wave characteristics. The wave properties of subatomic particles such as electrons and neutrons play important roles in their behavior, but larger particles such as Ping-Pong balls or automobiles do not behave like waves. The reason is the scale of the waves. For all except subatomic particles, the wavelengths involved are so short that we are unable to detect the wave properties. Example illustrates this. 

From 50 years to 100 years after Dalton proposed his theory, various discoveries showed that the atom is not indivisible, but really is composed of parts. Natural radioactivity and the interaction of electricity with matter are two different types of evidence for this subatomic structure. The most important subatomic particles are listed in Table 3-2, along with their most important properties. The protons and neutrons occur in a very tiny nucleus (plural, nuclei). The electrons occur outside the nucleus. 

X-rays, or gamma rays generated by nuclear decay. Ionizing radiation also includes several types of subatomic particles, such as beta radiation (high-energy electrons) and alpha radiation (helium ions) and others. Medical X-rays are an example of a common beneficial exposure to ionizing radiation. Nuclear radiation is used to generate electricity and cure disease, but is also an important element in military weapons. Uses of nuclear radiation pose serious issues of human exposure and environmental contamination. 

PSI PARTICLE. Discovery of this subatomic particle in 1974 was announced independently by Ting (Brookhaven National Laboratory) who named it the J particle and by B.D. Richter (Stanford) who named it the psi particle. The discovery of this particle resolved a number of important problems in particle physics. Intensive research on the psi particle was carried out by Richter and the Stanford group during 1975 and 1976 and is reported firsthand by Richter (Science, 196, 1286-1297.1977). As pointed out by Richter, the four-quark theoretical model became much more compelling with the discovery of the psi particles, The long life of the psi is explained by the fact that the decay of the psi into ordinary hadrons requires the conversion of both c and c into other quarks and antiquarks. See also Particles (Subatomic). 

A frequently asked question is What are the differences between nuclear physics and nuclear chemistry Clearly, the two endeavors overlap to a large extent, and in recognition of this overlap, they are collectively referred to by the catchall phrase nuclear science. But we believe that there are fundamental, important distinctions between these two fields. Besides the continuing close ties to traditional chemistry cited above, nuclear chemists tend to study nuclear problems in different ways than nuclear physicists. Much of nuclear physics is focused on detailed studies of the fundamental interactions operating between subatomic particles and the basic symmetries governing their behavior. Nuclear chemists, by contrast, have tended to focus on studies of more complex phenomena where statistical behavior is important. Nuclear chemists are more likely to be involved in applications of nuclear phenomena than nuclear physicists, although there is clearly a considerable overlap in their efforts. Some problems, such as the study of the nuclear fuel cycle in reactors or the migration of nuclides in the environment, are so inherently chemical that they involve chemists almost exclusively. 

To understand how electricity is formed, it is important to first understand what an atom is made of. All atoms are made of subatomic particles. Subatomic particles are particles that are smaller than atoms. The basic subatomic particles that make up atoms are protons, neutrons, and electrons. 

An understanding of the structure of the smallest particle of matter, the atom, is very important to understanding how chemical bonds form. Remember that inside the nucleus of the atom, there are subatomic particles called protons and neutrons. Orbiting the nucleus is another type of subatomic particle, called electrons. Electrons are the parts of the atom that take part in chemical bonding. Chemical bonds occur when atoms gain, lose, or share electrons. Chemical reactions happen when these chemical bonds are formed or when they are broken. 

So far, much of the discussion about the atom has concentrated on the nucleus and its protons and neutrons. What about electrons What is their importance to the atom Recall that electrons occupy the space surrounding the nucleus. Therefore, they are the first subatomic particles that are likely to interact when atoms come near one another. In a way, electrons are on the front lines of atomic interactions. The number and arrangement of the electrons in an atom determine how the atom will react, if at all, with other atoms. As you will learn in section 2.2, and throughout the rest of this unit, electrons are responsible for the chemical properties of the elements. 

The atom is composed of many types of subatomic particles, but only three types will be important in this course. Protons and neutrons exist in the atom s nucleus, and electrons exist outside the nucleus. The nucleus (plural, nuclei) is incredibly small, with a radius about one ten-thousandth of the radius of the atom itself. (If the atom were the size of a car, the nucleus would be about the size of the period at the end of this sentence.) The nucleus does not change during any ordinary chemical reaction. (Nuclear reactions are described in Chapter 21.) The protons, neutrons, and electrons have the properties listed in Table 3.1. These properties are independent of the atom of which the subatomic particles are a part. Thus, the atom is the smallest unit that has the characteristic composition of an element, and in that sense, it is the smallest particle of an element. 

One property of special importance is boron s ability to absorb neutrons. Neutrons are subatomic particles with no charge that occur in the nucleus of nearly all atoms. Boron atoms are able to absorb a large number of neutrons. This makes boron useful in the control rods of nuclear reactors. 

Experiments by several scientists in the mid-1800s led to the first change to Dalton s atomic theory. Scientists discovered that atoms can be broken into pieces after all. These smaller parts that make up atoms are called subatomic particles. Many types of subatomic particles have since been discovered. The three particles that are most important for chemistry are the electron, the proton, and the neutron. 

Recall from Table 4-1 that the masses of both protons and neutrons are approximately 1.67 x 10 g. While this is a very small mass, the mass of an electron is even smaller—only about that of a proton or neutron. Because these extremely small masses expressed in scientific notation are difficult to work with, chemists have developed a method of measuring the mass of an atom relative to the mass of a specifically chosen atomic standard. That standard is the carbon-12 atom. Scientists assigned the carbon-12 atom a mass of exactly 12 atomic mass units. Thus, one atomic mass unit (amu) is defined as the mass of a carbon-12 atom. Although a mass of 1 amu is very nearly equal to the mass of a single proton or a single neutron, it is important to realize that the values are slightly different. As a result, the mass of silicon-30, for example, is 29.974 amu, and not 30 amu. Table 4-2 gives the masses of the subatomic particles in terms of amu. 

The concept of the elements depended on two different but ultimately complementary ideas about matter. The first idea was ancient that the elements were the fundamental building blocks of nature. Whether there were 1, 2, 3, 4, or 92 elements was in a sense less important than the power of the concept to explain nature and direct research. The second idea came with the discovery of the structure of the atom and the physics that made that discovery possible that an element represented a specific combination of subatomic particles determined by physical laws. The creation of controlled nuclear fission and the invention of accelerators and cyclotrons made a kind of modem alchemy possible, allowing the creation of new elements that were not found in nature but that still met the new conditions to be considered elements. 

Many other subatomic particles, such as quarks, positrons, neutrinos, pions, and muons, have also been discovered. It is not necessary to study their characteristics to learn the fundamentals of atomic structure that are important in chemical reactions. 

From an electrostatic point of view, it is amazing that positively charged protons can be packed so closely together. Yet many nuclei do not spontaneously decompose, so they must be stable. In the early twentieth century when Rutherford postulated the nuclear model of the atom, scientists were puzzled by such a situation. Physicists have since detected many very short-lived subatomic particles (in addition to protons, neutrons, and electrons) as products of nuclear reactions. Well over 100 have been identified. A discussion of these many particles is beyond the scope of a chemistry text. Furthermore their functions are not entirely understood, but it is now thought that they help to overcome the proton-proton repulsions and to bind nuclear particles (nucleons) together. The attractive forces among nucleons appear to be important over only extremely small distances, about 10 cm. 

What is needed is a window that does not change the nature of the subatomic particles created in the collision. Beryllium is the element of choice, as it has a low atomic number, which means there are fewer protons and electrons to interfere electromagnetically. The element can be made into a metal more easily than hydrogen or lithium, and it is strong, even as a thin foil. This is important because accelerator beam pipes must be evacuated of air particles as much as possible to minimize unwanted collisions. So a huge pressure differential exists between the inside and outside of the beam pipe. Implosion would be a risk with a weaker material. 

Figure 2.7 shows the location of the elementary particles (protons, neutrons, and electrons) in an atom. There are other subatomic particles, but the electron, the proton, and the neutron are the three fundamental components of the atom that are important in chemistry. Table 2.1 shows the masses and charges of these three elementary particles. 

Of course, we recognize that progress in health is utterly dependent upon science and that ultimately all science, at least all natural science, springs from a common base. No research is so fundamental that we can say that it does not have and never will have relevance to health. Nevertheless, we must recognize a level sufficiently remote from biomedical research that its present contributions can have little if any import for the foreseeable future. For example, current work in subatomic particle physics is unlikely to have an early influence, despite the tremendous importance in biomedical research of the atomic physics of a generation ago. Few people would expect the NIH to support work in present-day atomic physics. 

The atom is now known to consist of three primary particles protons, neutrons, and electrons, which make up the atoms of all matter. A series of experimental facts established the validity of the model. Radioactivity played an important part. Marie Curie suggested, in 1899, that when atoms disintegrate, they contradict Dalton s idea that atoms are indivisible. There must then be something smaller than the atom (subatomic particles) of which atoms were composed. 

The word radiation was used until about 1900 to describe electromagnetic waves. Around the turn of the century, electrons. X-rays, and natural radioactivity were discovered and were also included under the umbrella of the term radiation. The newly discovered radiation showed characteristics of particles, in contrast to the electromagnetic radiation, which was treated as a wave. In the 1920s, DeBroglie developed his theory of the duality of matter, which was soon afterward proved correct by electron diffraction experiments, and the distinction between particles and waves ceased to be important. Today, radiation refers to the whole electromagnetic spectrum as well as to all the atomic and subatomic particles that have been discovered. 

To describe some important features of subatomic particles... 

O What is meant by the term chemical bond What subatomic particles are most important in bonds ... 

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