Acids atomic radius

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

These metals have an atomic radius below 1.3 A. Iron (1.16 A), chromium (1.17 A) and manganese (1.17 A) form carbides with properties intermediate between the salt-like and the interstitial. Structurally FcgC, MugC and NigC have C atoms inside the trigonal prisms formed by the metal atoms. They are easily decomposed by acids and water. In CrgC2 the carbon atoms form chains in the solid. 

Increases atomic radius, nuclear charge, ionic size, shielding effect, atomic number (number of protons, number of electrons), covalent character of halides, acidity of oxides... 

For example, the tripositive ions such as La or Pu show relatively little tendency to complex, but stable complexes are formed with the tetrapositive ions and with hydrated ions of hexapositive metals M02. The stability of the complex depends also on the properties of the complexing anion strongest complexes usually occur with anions of weak acids, or small atomic radius, and with large negative charge. The tendency of anions to form complexes increases approximately in the order... 

Small size favors hardness, other things being equal. Early consideration of hard and soft acids and bases did not go far beyond this conclusion. Until the direct relation between electronegativity and hardness was discovered, the atomic radius was associated with electronegativity rather than with hardness. Gordy (X oc Z/r [9]) and Allred and Rochow (x oc Z/r [10]) and Sanderson x ionic radius into their electronegativity... 

The properties which depend on the external electronic shell stmcture vary periodically with the Z number. The most important periodic properties are the atomic radius, the atomic volume, the ionic radius, the ionic volume, the melting point, the boiling point, the ionization energy, the electron affinity, the electronegativity, the valence, the acid-base character etc. (Aldea et al., 2000). 

Boron has a small atomic radius and a relatively high ionization energy. In consequence its chemistry is largely covalent and it is generaUy classed as a metalloid. It forms a large number of volatile hydrides, some of which have the uncommon bonding characteristic of electron-deficient compounds. It also forms a weakly acidic oxide. In some ways, boron resembles siUcon (see diagonal relationship). 

The hardness of an acid (acceptor) or a base (donor) is generally characterized by a small atomic radius, a high effective nuclear charge, and a low polarizability, whereas softness implies all the opposite properties. Furthermore, the softness of a base can be associated with low electronegativity, easy oxidizability, or empty low-lying orbitals. 

Both perchloric acid and sulfuric acid have an 0-H group, and the acidic proton is part of an 0-H unit for both acids. Any differences in bond strength may be due to differences in the sulfur versus the chlorine. The covalent radii of S is 102 pm and that of Cl is 99 pm, so there is minimal difference. If there is little difference in bond strength in the acids, there may be more subtle factors a simple expedient is to examine the conjugate bases. The hydrogen sulfate anion has an ionic radius of 221 ppm, whereas the perchlorate anion has an atomic radius of 225 ppm. There is little difference in the size of the anions. 

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