Periodic table radius

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides. 

The electron configuration or orbital diagram of an atom of an element can be deduced from its position in the periodic table. Beyond that, position in the table can be used to predict (Section 6.8) the relative sizes of atoms and ions (atomic radius, ionic radius) and the relative tendencies of atoms to give up or acquire electrons (ionization energy, electronegativity). 

In this section we will consider how the periodic table can be used to correlate properties on an atomic scale. In particular, we will see how atomic radius, ionic radius, ionization energy, and electronegativity vary horizontally and vertically in the periodic table. 

The decrease in atomic radius moving across the periodic table can be explained in a similar manner. Consider, for example, the third period, where electrons are being added to the third principal energy level. The added electrons should be relatively poor shields for each other because they are all at about the same distance from the nucleus. Only the ten core electrons in inner, filled levels (n = 1, n = 2) are expected to shield the outer electrons from the nucleus. This means that the charge felt by an outer electron, called the effective nuclear charge, should increase steadily with atomic number as we move across the period. As effective nuclear charge increases, the outermost electrons are pulled in more tightly, and atomic radius decreases. 

The radii of cations and anions derived from atoms of the main-group elements are shown at the bottom of Figure 6.13. The trends referred to previously for atomic radii are dearly visible with ionic radius as well. Notice, for example, that ionic radius increases moving down a group in the periodic table. Moreover the radii of both cations (left) and anions (right) decrease from left to right across a period. 

A radius of 128 pm corresponds to 1.28 X 10-8 cm, and the molar mass of copper (from the periodic table on the inside front cover) is 63.55 g-mol. The predicted density is therefore... 

Because carbon stands at the head of its group, we expect it to differ from the other members of the group. In fact, the differences between the element at the head of the group and the other elements are more pronounced in Group 14/IV than anywhere else in the periodic table. Some of the differences between carbon and silicon stem from the smaller atomic radius of carbon, which explains the wide occurrence of C=C and G=Q double bonds relative to the rarity of Si=Si and Si=0 double bonds. Silicon atoms are too large for the side-by-side overlap of p-orbitals necessary for -it-bonds to form between them. Carbon dioxide, which consists of discrete 0=C=0 molecules, is a gas that we exhale. Silicon dioxide (silica), which consists of networks of —O—Si- O - groups, is a mineral that we stand on. 

As the positive charge of the nucleus increases, the electrical force exerted by the nucleus on the negatively charged electrons increases, too, and electrons become more tightly bound. This in turn reduces the radius of the orbital. As a result, each orbital shrinks in size as atomic number increases. For example, the 2s orbital steadily decreases in size across the second row of the periodic table from Li (Z = 3 ) to Ne... 

One way that a solid metal can accommodate another is by substitution. For example, sterling silver is a solid solution containing 92.5% silver and 7.5% copper. Copper and silver occupy the same column of the periodic table, so they share many properties, but copper atoms (radius of 128 pm) are smaller than silver atoms (radius of 144 pm). Consequently, copper atoms can readily replace silver atoms in the solid crystalline state, as shown schematically in Figure 12-4. 

Figure 5.2 Atomic radius increases going down a column of the periodic table and generally decreases going across a row.

The Periodic Table forms one of the most remarkable, concise, and valuable tabulations of data in science. Its power lies in the regularities that it reveals, thus, in some respects, it has the same role as the SOM. Construct a SOM in which the input consists of a few properties of some elements, such as electronegativity, atomic mass, atomic radius, and electron affinity. Does the completed map show the kind of clustering of elements that you would expect What is the effect of varying the weight given to the different molecular properties that you are using ... 

Other rows in the periodic table follow a similar trend. However, for the third row, there is a general decrease in radius except for the last two or three elements in the transition series. The covalent radii of Fe, Co, Ni, Cu, and Zn are 126, 125, 124, 128, and 133 pm, respectively. This effect is a manifestation of the fact that the 3d orbitals shrink in size as the nuclear charge increases (going to the right), and the additional electrons populating these orbitals experience greater repulsion. As a result, the size decreases to a point (at Co and Ni), but after that the increase in repulsion produces an increase in size (Cu and Zn are larger than Co and Ni). 

Consider the element with atomic number 116 in Group 6A. Even though it has not been isolated, its atomic radius is expected to be somewhat larger than that of Po (1.68 A), probably about 1.9 - 2.0 A, since it lies just below Po on the periodic table. Its outer electrons would lie in the n=l shell, which would be further away from the nucleus than Po s outermost electrons in the n=6 shell. 

II. The general trend is for ionization energy to increase as one moves from left to right across the periodic table and to decrease as one moves down this is the inverse of the trend one finds in examining the atomic radius. 

As it is mentioned, electronegativity is dependent upon atomic radius. In the periodic table, as a period is crossed from left to right, atomic radius decreases, and hence the ability of an atom to attract valence electrons increases. However, as you descend a group, atomic radius increases and therefore ability of an atom to attract valence electrons decreases. So consequently, electronegativity decreases from top to bottom in a group and increases from left to right across a period. 

How does the atomic radius affect the ionization energies of the elements in a family on the periodic table ... 

Figure 4.14. Atomic dimensions of the elements. In this scheme each element, represented in its position of the Periodic Table, is indicated by a circle the diameter of which is roughly proportional to the atomic radius for coordination 12 (Teatum etal. 1968).

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