Valence, periodic trends

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). 

Polarizability shows periodic variations that correlate with periodic trends in how tightly valence electrons are bound to the nucleus ... 

Atomic radius is approximately the distance from the nucleus of an atom to the outside of the electron cloud where the valence electrons are formd. The reactivity of the -atom depends on how easily the valence electrons can be removed, and that depends on their distance from the attractive force of the nucleus. In this MiniLab, you will study the periodic trends in the atomic radii of the first 36 main group elements from hydrogen through barimn. 

There are periodic trends that can be seen in the periodic table, the first of which deals with the stability of atoms according to the number of outer electrons in the atom. This is known as valency, and it can be used to show why some atoms are more reactive than others. There are many more periodic trends that are associated with the electrons around the atoms, and you can find more examples in Chapter 2. 

In this chapter, we have tried to emphasize general aspects of main-group chemical bonding, with particular emphasis on periodic trends. The periodic table remains the most important classification tool in chemistry, and it is crucial to understand even subtle secondary periodicities if one is to make efficient use of the various elements for different chemical applications. The radial nodal structure of the valence orbitals has been pointed out to account for more of the known trends than most practitioners of chemistry are aware of. For example, the inversion barriers of phosphines or silyl anions, the dependence of the inert-pair effect on the electronegativity of the substituents, the stability of carbene- or carbyne-type species or of multiple bonds between heavy main-group elements are aU intricately linked to hybridization defects of s- and p-valence orbitals of disparate sizes. Even the question of hypervalency is closely connected to the effects of primogenic repulsion . 

The lanthanide contraction explains which of the following periodic trends (a) The atomic radii of the transition metals first decrease and then increase when moving horizontally across each period, (b) When forming ions the transition metals lose their valence s orbitals before their valence d orbitals, (c) The radii of the period 5 transition metals (Y-Cd) are very similar to the radii of the period 6 transition metals (Lu-Hg). 

Which periodic trend is responsible for the observation that the maximum oxidation state of the transition-metal elements peaks near groups 7B and 8B (a) The number of valence electrons reaches a maximum at group 8B. (b) The effective nuclear charge increases on moving left across each period,... 

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