Periodic trends charge

Atomic radii typically decrease from left to right across a period and increase down a group (Fig. 14.2 see also Fig. 1.46). As the nuclear charge experienced by the valence electrons increases across a period, the electrons are pulled closer to the nucleus, so decreasing the atomic radius. Down a group the valence electrons are farther and farther from the nucleus, which increases the atomic radius. Ionic radii follow similar periodic trends (see Fig. 1.48). 

The physical and chemical properties of the elements show regular periodic trends that can be explained using electron configurations and nuclear charges. We focus on the physical properties of the elements in this section. A preliminary discussion of the chemical properties of some of the elements appears in Section Other chemical properties are discussed after we introduce the principles of chemical bonding in Chapters 9 and 10. 

Current results for sample correlations will be compared and observed periodic trends, and trends according to charge-type, will be discussed. 

Recall from Chapter 2 that a gradual change in properties as we move in any direction in the periodic table is called a periodic trend. Most periodic trends can be understood from the perspective of the simplified shell model, and underlying most trends are two important concepts inner-shell shielding and effective nuclear charge. 

Periodic trends—Going from left to right across a period, atomic size tends to decrease. This occurs because of an increase in nuclear charge, which pulls the electrons in more tightly (thus making the atoms smaller). The noble gases are the smallest elements in each period. 

Periodic trends—Ionization energies increase going from left to right across a period. This is because of the increase in nuclear charge. As the nuclear charge increases, the attraction between the electrons and the nucleus increases. This makes it more difficult to remove an electron from the atom. 

Answer N and P represent group trends, while N and O represent periodic trends. N is more electronegative than P (less shielding), while O is more electronegative than N (greater effective nuclear charge). Therefore, P < N < O. 

In this work, we discuss the results of DFT calculations for some all-metal clusters with the general formula MAI/ at a validated level of theory and numerical precision and compute a number of accepted properties to describe aromaticity, such as 17, geometrical parameters, the DI, and the NICS indexes. Hereby, we pursue the evaluation of DFT calculations and reactivity descriptors to explain and assess aromaticity in the anionic all-metal clusters derived from the Al/- unit. We determine the effect of different charges and multiplicities on the geometry of Al/(n = —2, —1,0,1) and calculate the structures of new complexes MA14" where M = (Li+, Na+, K+), (Be+2, Mg+2, Ca+2), (Sc+3, Ti+4), and (B+3, Al+3, Ga+3). In order to compare the DFT reactivity descriptors, we compute other parameters (NICS and DIs) and study periodic trends. 

With Zef( in mind, we can make general predictions about the elements based upon their position in the periodic table. The totalities of these predictions are called the periodic trends. Since the effective nuclear charge increases when moving from left to right, each additional electron is pulled more strongly toward the nucleus. This results in a smaller atomic radius Of course, with each added shell the atom grows larger. Thus, atomic radius also increases from the top of the periodic table to the bottom. 

The effective nuclear charge, Zg , experienced by an electron in an outer shell is less than the actual nuclear charge, Z. This is because the attraction of outer-shell electrons by the nucleus is partly counterbalanced by the repulsion of these outer-shell electrons by electrons in inner shells. We say that the electrons in inner shells screen, or shield, electrons in outer shells from the full effect of the nuclear charge. This concept of a screening, or shielding, effect helps us understand many periodic trends in atomic properties. 

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