Nucleus of an atom

The nucleus of an atom is made up of protons and neutrons in a cluster. Virtually all the mass of the atom resides in the nucleus. The nucleus is held together by the tight pull of what is known to chemists and physicists as the "strong force." This force between the protons and neutrons overcomes the repulsive electrical force that would, according to the rules of electricity, push the protons apart otherwise. 

FIGURE 3.1 Two arrangements of electrons around the nucleus of an atom having the same probability within HF theory, but not in correlated calculations. 

The Fermi contact density is defined as the electron density at the nucleus of an atom. This is important due to its relationship to analysis methods dependent... 

Atomic number The number of protons in the nucleus of an atom of an element. Also, the number of electrons in a neutral atom of the element. 

Bela particle emission occurs when an ordinary electron is ejected from tlie nucleus of an atom. Tlie electron (e) appears when a neutron (n) is tTcUisformcd into a proton witliin tlie nucleus. 

Beta piuticle emission occurs when an ordinary electron is ejected from tlie nucleus of an atom. 

The nucleus of an atom consists of protons and neutrons that are bound together by a nuclear force. Neutrons and protons are rearranged in a nuclear reaction in a manner somewhat akin to rearrang ing atoms in a chemical reaction. The nuclear reaction liberating energy in a nuclear power plant is called nuclear fission. The word fission is derived from fissure, which means a crack or a separation. A nucleus is separated (fissioned) into two major parts by bombardment with a neutron. 

Since Rutherford s time scientists have learned a great deal about the properties of atomic nuclei. For our purposes in chemistry, the nucleus of an atom can be considered to consist of two different types of particles (Table 2.1) ... 

The nucleus carries a positive electric charge. The element hydrogen has the lightest atoms, and the nuclei of these atoms have the smallest positive charge anyone has observed. Every atom of hydrogen has one proton in its nucleus. The charge on the nucleus of an atom of hydrogen... 

FIGURE Bj4 Think of a fly at the center of this stadium that is the relative size of the nucleus of an atom if the atom were magnified to the size of the stadium. 

J 9 Assess the relative probability of finding an electron at a given distance from the nucleus of an atom (Example 1.9). 

To improve our model we note that s- and /7-orbitals are waves of electron density centered on the nucleus of an atom. We imagine that the four orbitals interfere with one another and produce new patterns where they intersect, like waves in water. Where the wavefunctions are all positive or all negative, the amplitudes are increased by this interference where the wavefunctions have opposite signs, the overall amplitude is reduced and might even be canceled completely. As a result, the interference between the atomic orbitals results in new patterns. These new patterns are called hybrid orbitals. Each of the four hybrid orbitals, designated bn, is formed from a linear combinations of the four atomic orbitals ... 

What Are the Key Ideas Changes in the nucleus of an atom can result in the ejection of particles, the transformation of the atom into another element, and the release of energy. 

Fig. 17.7), is therefore the nucleus of an atom of a different element. For example, when a radon-222 nucleus emits an a particle, a polonium-218 nucleus is formed. In this case, a nuclear transmutation, the conversion of one element into another, has taken place. Another important difference between nuclear and chemical reactions is that energy changes are very much greater for nuclear reactions than for chemical reactions. For example, the combustion of 1.0 g of methane produces about 52 kj of energy as heat. In contrast, a nuclear reaction of 1.0 g of uranium-235 produces about 8.2 X 10 kj of energy, more than a million times as much. 

MASS NUMBER The sum of the number of protons and neutrons in the nucleus of an atom. 

A second sun, powerful and man-made, was born on July 16, 1945. A ball of fire thousands of times hotter than the surface of the real sun illuminated the New Mexico desert. Its birthplace was the Trinity site, and the explosion was the culmination of years of work by the world s brightest scientists. It was the planet s first atomic bomb, the tangible and frightening outcome of splitting the nucleus of an atom. 

When the energy in the nucleus of an atom is released, the results are spectacular. Atomic bombs and reactors that power entire cities grab everyone s attention. But most of the everyday world is governed by an atom s electrons, the swirling cloud of negatively charged matter that can act as particles or waves. 

Binding energy A measure of the strength of the force holding the nucleons together in the nucleus of an atom. The term is sometimes applied to the force holding an electron in an atom. 

Electron A negatively charged particle found outside the nucleus of an atom. Free electrons are called beta particles. 

Beta Particle—An electron that is emitted from the nucleus of an atom during one type of radioactive transformation. A beta particle has a mass and charge equal in magnitude to that of the electron. The charge may be either +1 or -1. Beta particles with +1 charges are called positrons (symbolized (3+), and beta particles with -1 charges are called negatrons (symbolized (3 ). 

Figure 2.2 Electrons travel around the nucleus of an atom and are located in a series of energy levels, or shells, that increase in energy as their distance from the nucleus increases.

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