Nuclear charge elements

For elements with lower nuclear charges than tin, the aj-a2 splitting is smaller because of the reduced spin-orbit coupling. For example for calcium, with Z = 20, the splitting is only about 3 eV and usually unresolved. 

Elemental sensitivity Scales as the square of nuclear charge best for heavy elements (< 10 monolayer) poor for hydrogen... 

Table 5.1 lists some of the atomic properties of the Group 2 elements. Comparison with the data for Group 1 elements (p. 75) shows the substantial increase in the ionization energies this is related to their smaller size and higher nuclear charge, and is particularly notable for Be. Indeed, the ionic radius of Be is purely a notional figure since no compounds are known in which uncoordinated Be has a 2- - charge. In aqueous solutions the reduction potential of... 

We often say that an electron is a spin-1/2 particle. Many nuclei also have a corresponding internal angular momentum which we refer to as nuclear spin, and we use the symbol I to represent the vector. The nuclear spin quantum number I is not restricted to the value of 1/2 it can have both integral and halfintegral values depending on the particular isotope of a particular element. All nuclei for which 7 1 also posses a nuclear quadrupole moment. It is usually given the symbol Qn and it is related to the nuclear charge density Pn(t) in much the same way as the electric quadrupole discussed earlier ... 

Since the diagonal elements depend only on the nature of the atom (i.e. the nuclear charge), this means that for example all carbon atoms have the same ability to attract electrons. After having performed a Hiickel calculation, the actual number of electrons associated with atom A, / a, can be calculated according to eq. (3.90) (see section 9.1, eqs. (9.5) and (9.4)). 

Now our nuclear model suffices. We can build up the atoms for all elements. Each atom has a nucleus consisting of protons and neutrons. The protons are responsible for all of the nuclear charge and part of the mass. The neutrons are responsible for the rest of the mass of the nucleus. The neutron plays a role in binding the nucleus together, apparently adding attractive forces which predominate over the electrical repulsions among the protons. ... 

Thus, each of the chemical elements consists of atoms whose nuclei contain a particular number of protons, hence a particular nuclear charge. The number of protons in the nucleus is called the... 

The nuclear charge and the electrons it attracts primarily determine the ways in which atoms behave toward other atoms. Mass differences cause only minor chemical effects. Since the isotopes of an element have the same nuclear charge and the same number of electrons per neutral atom, they react in the same ways. Thus we can speak of the chemistry of oxygen without specifying which one of the three stable isotopes is reacting. Only the most precise measurements will indicate the very slight chemical differences among them. 

The difference is caused by the higher nuclear charge of magnesium. Magnesium is element 12, hence it has twelve protons in the nucleus, com-... 

ELEMENT SYMBOL NUCLEAR CHARGE inner electrons valence electrons ionization ENERGY, El (kcal/mole)... 

ELEMENT SYMBOL NUCLEAR CHARGE INNER LEVELS OUTER LEVELS... 

Ionization energy. As ionization energies go, the values found for the transition elements are neither very high nor very low. They are all rather similar in magnitude. The sequential increase in nuclear charge, which would tend to increase the ionization energy, seems to be almost offset by the extra screening of the nucleus provided by the added electrons. 

The very slight differences that do exist among these elements are due to small changes in size brought about by increase of nuclear charge. The separation of the lanthanide elements from each other is based upon clever exploitation of these slight differences in properties. Table 23-1 shows a comparison of some of the properties of the various lanthanide elements. As can be seen, +3 is the common oxidation number and is most characteristic of the chemistry of these elements. Another thing to note is the steady decrease in... 

Astrophysical spectroscopic element or elemental atom Physical atoms in vacuum specified by the nuclear charge. 

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. 

FIGURE 1.47 The periodic variation in the atomic radii of the elements. The variation across a period can be explained in terms of the effect of increasing effective nuclear charge that down a group by the occupation of shells with inc reasing principal quantum number. 

SOLUTION The smaller member of a pair of isoelectronic ions in the same period will be an ion of an element that lies farther to the right in a period, because that ion has the greater effective nuclear charge. If the two ions are in the same group, the smaller ion will be the one that lies higher in the group, because its outermost electrons are closer to the nucleus. Check your answer against the values in Appendix 2C. 

All the elements in a main group have in common a characteristic valence electron configuration. The electron configuration controls the valence of the element (the number of bonds that it can form) and affects its chemical and physical properties. Five atomic properties are principally responsible for the characteristic properties of each element atomic radius, ionization energy, electron affinity, electronegativity, and polarizability. All five properties are related to trends in the effective nuclear charge experienced by the valence electrons and their distance from the nucleus. 

Fig. 1.—Values of the metallic radius for ligancy 12, represented by circles, for the elements yttrium to silver. The straight line represents the expected values for valence of other metals equal to the valence of molybdenum that is, it shows the effect of increasing nuclear charge only.

As stated in Chapter the periodic table lists elements in order of increasing masses, with a few exceptions. In fact, nuclear charge is the organizing feature of the periodic table. As nuclear charge increases, so also does nuclear mass (with few exceptions), so... 

The periodic table is a catalog of the elements, each with its own unique set of physical and chemical properties. Each element has a unique value for Z, the positive charge on its nucleus. The number of electrons possessed by a neutral atom of that element is also equal to Z. The different properties of elements arise from these variations in nuclear charges and numbers of electrons. 

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