Particles subatomic

Small as atoms are, they in turn consist of even smaller entities called subatomic particles. Although physicists have found sevmd dozen of these, chemists need consider only three—protons, neutrons, and electrons (these were introduced briefly in Section 1.5). These subatomic particles differ in mass and charge. Like the atom, their masses are expressed in atomic mass units. 

The proton, p, has a mass of 1.007277 u and a unit charge of +1. This charge is equal to 1.6022 X 10 ° coulombs, where a coulomb is the amount of electrical charge involved in a flow of electrical current of 1 ampere for 1 second. 

The neutron, n, has no electrical charge and a mass of 1.009665 u. The proton and neutron each have a mass of essentially 1 u and are said to have a mass number of 1. (Mass number is a useful concept expressing the total number of protons and neutrons, as well as the approximate mass, of a nucleus or subatomic particle.) 

Subatomic Particle Symbol Unit Charge Mass Number Mass (u) Mass (g) 

The mass number and charge of each of these kinds of particles can be indicated by a superscript and subscript, respectively in the symbols p, Jn, Je. 

The atom is the smallest part of matter that represents a particular element. For quite a while, the atom weis thought to be the smallest part of matter that could exist. But in the latter part of the 19th century and early part of the 20th, scientists discovered that atoms are composed of certain subatomic particles and that no matter what the element, the same subatomic particles make up the atom. The number of the various subatomic particles is the only thing that varies. 

Scientists now recognize that there are many subatomic particles (this really makes physicists salivate). But to be successful in chemistry, you really only need to be concerned with the three major subatomic particles  

Name Symbol Charge Mass (g) Mass (amu) Location 

Atomic mass units are based on something called the carbon-12 scale, a worldwide stcindard that s been adopted for atomic weights. By international agreement, a carbon atom that contains six protons and six neutrons has an atomic weight of exactly 12 amu, so 1 amu is defined as Vn of this carbon atom. Because the masses in grams of protons and neutrons are almost exactly the same, both protons and neutrons are said to have a mass of 1 amu. Notice that the mass of cin electron is much smaller than that of either a proton or neutron. It takes almost 2,000 electrons to equal the mass of a single proton. 

Scientists have discovered through observation that objects with like charges, whether positive or negative, repel each other, cind objects with unlike charges attract each other. 

In chemistry, the term nucleus (plural nuclei) is used for atoms as it is used for the nucleus of a cell in biology. 

In an atom sphere, there is a nucleus at the center. An atom s nucleus contains protons and neutrons. Electrons are also found in an atom, but they move so quickly that we only know that they are around the nucleus but not exactly where  

Proton (p) Positively charged particles found in the nucleus of an atom. Neutron (n) Uncharged particles found in the nucleus of an atom. Electron (e ) Negatively charged particles found around the nucleus of an atom (Table 1). 

Amu atomic mass unit 1 amu means 1/12 of the mass of a carbon - 12 nucleus. 

1 Coulomb (C) Amount of electrical charge carried by a current of 1 ampere (A) in 1 second. 

As with many new ideas, Dalton s theory was not immediately accepted. However, it led to a prediction that must be true if the theory is correct. This is now known as the Law of Multiple Proportions. It states that when two elements combine to form more than one compound, the different weights of one element that combine with the same weight of the other element are in a simple ratio of whole numbers (Fig. 5.2). This is like threading one, two, or three identical nuts onto the same bolt. The mass of the bolt is constant. The mass of two nuts is twice the mass of one the mass of three nuts is three times the mass of one. The masses of nuts are in a simple ratio of whole numbers, 1 2 3. 

The multiple proportion prediction can be confirmed by experiment. Using a theory to predict something unknown and having the prediction confirmed is convincing evidence that the theory is correct. With supporting evidence such as this, Dalton s 

In an experiment to confirm the Law of Multiple Proportions, a scientist finds that sulfur and oxygen form two different compounds. In each experiment, 1.0 g of sulfur is allowed to react with oxygen. Under one set of conditions, 0.5 g of oxygen reacts, and under another set of conditions, 1.0 g of oxygen reacts. Do these data confirm the Law of Multiple Proportions Explain. 

2 Identify the three major subatomic particles by charge and approximate atomic mass, expressed in atomic mass units. 

The second subatomic particle, the proton, was isolated and identified in 1919 by Ernest Rutherford. Its mass is 1836 times greater than the mass of an electron. The 

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A positively charged subatomic particle equivalent to a helium nucleus (a). 

A charged subatomic particle produced when a neutron converts to a proton, or a proton converts to a neutron (p). 

Radioactive materials Elements that have unstable nuclei that spontaneously disintegrate, releasing radiation in the form of subatomic particles and energy. 

The development of particle accelerators grew out of the discovery of radioactivity in uranium by Henri Becquerel in Paris in 1896. Some years later, due to the work of Ernest Rutherford and others, it was found that the radioactivity discovered by Becquerel was the emission o particles with kinetic energies o several MeV from uranium nuclei. Research using the emitted particles began shortly thereafter. It was soon realized that if scientists were to learn more about the properties of subatomic particles, they had to be accelerated to energies greater than those attained in natural radioactivity. 

If subatomic particles moving at speeds close to the speed of light collide with nuclei and electrons, new phenomena take place that do not occur in collisions of these particles at slow speeds. For example, in a collision some of the kinetic energy of the moving particles can create new particles that are not contained in ordinaiy matter. Some of these created particles, such as antiparticles of the proton and elec-... 

As you probably know, an atom consists of a dense, positively charged nucleus surrounded at a relatively large distance by negatively charged elections (Figure 1.2). The nucleus consists of subatomic particles called neutrons, which are electrically neutral, and protons, which are positively charged. Because an atom is neutral... 

Subatomic particles, such as electrons and nuclei, arc introduced in Section B. 

The observation that atoms of a single element can have different masses helped scientists refine the nuclear model still further. They realized that an atomic nucleus must contain subatomic particles other than protons and proposed that it also contains electrically neutral particles called neutrons (denoted n). Because neutrons have no electric charge, their presence does not affect the nuclear charge or the number of electrons in the atom. However, they do add substantially to the mass of the nucleus, so different numbers of neutrons in a nucleus give rise to atoms of different masses, even though the atoms belong to the same element. As we can see from Table B.l, neutrons and protons are very similar apart from their charge they are jointly known as nucleons. 

B.9 An unstable atomic nucleus gives off nuclear radiation consisting of particles that have a mass of about 1.7 X 10 kg. The particles are attracted to a negatively charged plate. The radiation consists of what type of subatomic particle ... 

B.10 (a) What characteristics do atoms of carbon-12, carbon-13, and carbon-14 have in common (b) In what ways are they different (Consider the numbers and types of subatomic particles.)... 

Dalton pictured atoms as featureless spheres, like billiard balls. Today, we know that atoms have an internal structure they are built from even smaller subatomic particles. In this book, we deal with the three major subatomic particles the electron, the proton, and the neutron. By investigating the internal structure of atoms, we can come to see how one element differs from another and see how their properties are related to the structures of their atoms. 

The earliest experimental evidence for the internal structure of atoms was the discovery in 1897 of the first subatomic particle, the electron. The British physicist... 

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. 

Since Rutherford s work, scientists have identified other types of nuclear radiation. Some consist of rapidly moving particles, such as neutrons or protons. Others consist of rapidly moving antiparticles, particles with a mass equal to that of one of the subatomic particles but with an opposite charge. For example, the positron has the same mass as an electron but a positive charge it is denoted 3 or f e. When an antiparticle encounters its corresponding particle, both particles are annihilated and completely converted into energy. Table 17.1 summarizes the properties of particles commonly found in nuclear radiation. 

Chemical advances frequently are driven by technology. The discovery that atoms have inner structure was an outgrowth of the technology for working with radioactive materials. In Chapter 2 we describe a famous experiment in which the structure of atoms was studied by bombarding a thin gold foil with subatomic particles. A contemporary example is the use of lasers to study the details of chemical reactions. We introduce these ideas in Chapters 7 and 8. 

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. 

Neutron A subatomic particle found in the nuclei of atoms. It is electrically neutral with a mass that is slightly greater than that of a proton. 

Proton The positively charged subatomic particle found in the nucleus of atoms. 

Electron A negatively charged subatomic particle found traveling around the outside of an atom s nucleus in energy levels, or shells. 

Classic popular account of great chemists Trevisan, Paracelsus, Avogadro, Mendeleeff, Curies, Thomson, Lawrence, up to A-bomb research, recent work with subatomic particles"... 

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