Atomic radius table

The data in Table 7.1 show that, as expected, density, ionic radius, and atomic radius increase with increasing atomic number. However, we should also note the marked differences in m.p. and liquid range of boron compared with the other Group III elements here we have the first indication of the very large difference in properties between boron and the other elements in the group. Boron is in fact a non-metal, whilst the remaining elements are metals with closely related properties. 

The atom radius of an element is the shortest distance between like atoms. It is the distance of the centers of the atoms from one another in metallic crystals and for these materials the atom radius is often called the metal radius. Except for the lanthanides (CN = 6), CN = 12 for the elements. The atom radii listed in Table 4.6 are taken mostly from A. Kelly and G. W. Groves, Crystallography and Crystal Defects, Addison-Wesley, Reading, Mass., 1970. 

Only body-centered cubic crystals, lattice constant 428.2 pm at 20°C, are reported for sodium (4). The atomic radius is 185 pm, the ionic radius 97 pm, and electronic configuration is lE2E2 3T (5). Physical properties of sodium are given ia Table 2. Greater detail and other properties are also available... 

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. 

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. 

In other crystals an octahedral metal atom is attached to six non-metal atoms, each of which forms one, two, or three, rather than four, bonds with other atoms. The interatomic distance in such a crystal should be equal to the sum of the octahedral radius of the metal atom and the normal-valence radius (Table VI) of the non-metal atom. This is found to be true for many crystals with the potassium chlorostannate (H 61) and cadmium iodide (C 6) structures (Table XIB). Data are included in Table XIC for crystals in which a tetrahedral atom is bonded to a non-metal atom with two or three covalent bonds. The values of dcalc are obtained by adding the tetrahedral radius for the former to the normal-valence radius for the latter atom. 

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 ... 

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. 

Further investigation of allylpotassium complexes have shown that 2-isopropylallyl potassium does not show diastereotopism of the methyl groups at temperatures as low as —155 °C54,59. Therefore, the activation barrier for interconversion is on the order of 4 kcal mol 1 or lower. Both crotyl (19) and prenyl (20) potassium complexes are further examples of the preference for allylpotassium compounds to exist as symmetric it species. The potassium has the appropriate atomic radius to reach both C(i) and C(3). No increase in stabilization is gained upon addition of solvent. Allylcesium behaves in the same manner. In general, the theoretically calculated rotational barriers (Table 9) are higher... 

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).

Subsequently, the lattice parameters of Al(Mg) were calculated as shown in Table 3.1. It is clear that the lattice parameter of Al in the powders milled for 10 h is much larger after heating in DSC up 295, 350 and 425°C than that of the sample heated up to 180°C. The lattice expansion is consistent with the magnitude of the atomic radius of Al and Mg which is equal to 0.1432 and 0.1604 nm, respectively [121]. Fossdal et al. [114] claimed the formation of the Al(Mg) solid solution during low-temperature desorption of Mg(AlH4)2 below 180°C which is not confirmed here. Mamatha et al. [117, 118] never reported the formation of the Al(Mg) solid solution although Kim et al. [119] mentioned about increase in the lattice parameter of Al most probably due to formation of the Al(Mg) solid solution. 

The Pauling electronegativities of carbon and tellurium are, respectively, 2.5 and 2.1. This, in addition to the large volume of the tellurium atom (atomic radius 1.37, ionic radius 2.21), promotes easy polarization of Te-C bonds. The ionic character of the bonds increases in the order C(sp ) Te>C(sp ) Te>C(sp)-Te, in accordance with the electronegativity of carbon accompanying the s character (Table 1.1). 

For continuity, the neutral Ne atom is also in the chart, with its atomic radius. As you proceed to the right in Table 5-5, the greater number of protons attracts the electrons more strongly, producing progressively smaller ions. 

The reduced flexibility of such ligands may prevent them from satisfying a preference for a given coordination number, i. e. a fixed number n of coordination sites is offered to the cation (strait-jacketing). Now, the mutual repulsion of the n coordinating atoms precludes their contact with cations smaller than a certain critical radius (97). For cations smaller than this minimal cavity radius (Table 8) the interaction with... 

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