Ionic radius 2072281 197416979 2008-03-11T05:38:36Z Dreadstar 690391 Reverted edits by [[Special:Contributions/24.24.214.205|24.24.214.205]] ([[User talk:24.24.214.205|talk]]) to last version by 219.79.53.225 {{Atomic radius}} The '''ionic radius''', ''r''<sub>ion</sub>, is a measure of the size of an [[ion]] in a [[crystal lattice]]. It is measured in either [[picometre]]s (pm) or [[Angstrom (unit)|Angstrom]] (Å), with 1&nbsp;Å&nbsp;= 100&nbsp;pm. Typical values range from 30&nbsp;pm (0.3&nbsp;Å) to over 200&nbsp;pm (2&nbsp;Å). The concept of ionic radius was developed independently by Goldschmidt and [[Linus Pauling|Pauling]] in the 1920s to summarize the data being generated by the (then) new technique of [[X-ray crystallography]]: it is Pauling's approach which proved to be the more influential. X-ray crystallography can readily give the length of the side of the [[unit cell]] of a crystal, but it is much more difficult (in most cases impossible, even with more modern techniques) to distinguish a boundary between two ions. For example, it can be readily determined that each side of the unit cell of [[sodium chloride]] is 564.02&nbsp;pm in length, and that this length is twice the distance between the centre of a sodium ion and the centre of a [[chloride]] ion: ::2[''r''<sub>ion</sub>(Na<sup>+</sup>) + ''r''<sub>ion</sub>(Cl<sup>&minus;</sup>)] = 564.02&nbsp;pm However, it is not apparent what proportion of this distance is due to the size of the sodium ion and what proportion is due to the size of the chloride ion. By comparing many different compounds, and with a certain amount of chemical intuition, Pauling decided to assign a radius of 140&nbsp;pm to the [[oxide]] ion O<sup>2&minus;</sup>, at which point he was able to calculate the radii of the other ions by subtraction.<ref name="NOTCB">[[Linus Pauling|Pauling, L.]] (1960). ''[[The Nature of the Chemical Bond]]'' (3rd Edn.). [[Ithaca, NY]]: Cornell University Press.</ref> A major review of crystallographic data led to the publication of a revised set of ionic radii in 1976,<ref name="Shannon">'' Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides'' Shannon R.D. Acta Cryst. A32 751-767 (1976) {{doi|10.1107/S0567739476001551}}</ref> and these are preferred to Pauling's original values. Some sources have retained Pauling's reference of ''r''<sub>ion</sub>(O<sup>2&minus;</sup>)&nbsp;= 140&nbsp;pm, while other sources prefer to list "effective" ionic radii based on ''r''<sub>ion</sub>(O<sup>2&minus;</sup>)&nbsp;= 126&nbsp;pm. The latter values are thought to be a more accurate approximation to the "true" relative sizes of [[anion]]s and [[cation]]s in [[ionic crystal]]s. The ionic radius is not a fixed property of a given ion, but varies with [[coordination number]], [[spin state]] and other parameters. Nevertheless, ionic radius values are sufficiently [[Transferability|transferable]] to allow [[Periodicity|periodic trends]] to be recognized. As with other types of [[atomic radius]], ionic radii increase on descending a [[Periodic table group|group]]. Ionic size (for the same ion) also increases with increasing coordination number, and an ion in a [[high-spin]] state will be larger than the same ion in a [[low-spin]] state. Anions (negatively charged) are almost invariable larger than cations (positively charged), although the [[fluoride]]s of some [[alkali metal]]s are rare exceptions. In general, ionic radius decreases with increasing positive charge and increases with increasing negative charge. {| class="wikitable" align=right width=200px |- ! align=left | X<sup>&minus;</sup> ! NaX ! AgX |- | F | 464 | 492 |- | Cl | 564 | 555 |- | Br | 598 | 577 |- | colspan=3 |<small>Unit cell parameters (in [[picometre|pm]], equal to two M&ndash;X bond lengths) for sodium and silver halides. All compounds crystallize in the NaCl structure.</small> |- |} An "anomalous" ionic radius in a crystal is often a sign of significant [[Covalent bond|covalent]] character in the bonding. No bond is ''completely'' ionic, and some supposedly "ionic" compounds, especially of the [[transition metal]]s, are particularly covalent in character. This is illustrated by the [[unit cell parameter]]s for [[sodium]] and [[silver]] [[halide]]s in the table. On the basis of the fluorides, one would say that Ag<sup>+</sup> is larger than Na<sup>+</sup>, but on the basis of the [[chloride]]s and [[bromide]]s the opposite appears to be true.<ref>On the basis of conventional ionic radii, Ag<sup>+</sup> (129&nbsp;pm) is indeed larger than Na<sup>+</sup> (116&nbsp;pm)</ref> This is because the greater covalent character of the bonds in AgCl and AgBr reduces the bond length and hence the apparent ionic radius of Ag<sup>+</sup>, an effect which is not present in the halides of the more [[electronegativity|electropositive]] sodium, nor in [[silver fluoride]] in which the fluoride ion is relatively [[Polarizability|unpolarizable]]. {|class="wikitable sortable" cellpadding="2" |+Ionic radii 6 coordinate unless marked<br>(e.g '''+3<sup>4</sup>'''). ''ls'' = low spin, ''hs''= high spin. <ref name = "Shannon"/> |- !Atomic No !Element ! !width="90" |charge ionic radius [[picometer|pm]] |- |3 |[[Lithium]] |Li | {| |'''+1'''|| 76 |} |- |4 |[[Beryllium]] |Be | {| |'''+2'''|| 45 |} |- |5 |[[Boron]] |B | {| |'''+3''' ||27 |} |- |6 |[[Carbon]] |C | {| |'''+4'''|| 16 |} |- |7 |[[Nitrogen]] |N | {| |'''<nowiki>&minus;</nowiki>3'''<sup>4</sup>||align="right" width="50%"|146 |- |'''+3''' ||align="right" width="50%"|16 |- |'''+5''' ||align="right" width="50%"|13 |} |- |8 |[[Oxygen]] |O | {| |'''<nowiki>&minus;</nowiki>2''' ||140 |} |- |9 |[[Fluorine]] |F | {| |'''<nowiki>&minus;</nowiki>1'''||align="right" width="50%"| 133 |- | '''+7'''||align="right" width="50%"| 8 |} |- |11 |[[Sodium]] |Na | {| |'''+1''' ||102 |} |- |12 |[[Magnesium]] |Mg | {| |'''+2''' ||72 |} |- |13 |[[Aluminum]] |Al | {| |'''+3''' ||53.5 |} |- |14 |[[Silicon]] |Si | {| |'''+4'''||40 |} |- |15 |[[Phosphorus]] |P | {| |'''+3'''||44 |- | '''+5'''||38 |} |- | 16 |[[Sulfur]] |S | {| |'''<nowiki>&minus;</nowiki>2'''||align="right" width="50%"|184 |- |'''+4'''||align="right" width="50%"|37 |- | '''+6'''||align="right" width="50%"|29 |} |- | 17 |[[Chlorine]] |Cl | {| |'''<nowiki>&minus;</nowiki>1'''||align="right" width="50%"|181 |- |'''+5'''||align="right" width="50%"|12 |- |'''+7'''||align="right" width="50%"| 27 |} |- | 19 |[[Potassium]] |K | {| |'''+1'''|| 138 |} |- | 20 |[[Calcium]] |Ca | {| |'''+2'''|| 100 |} |- | 21 |[[Scandium]] |Sc | {| |'''+3'''|| 74.5 |} |- | 22 |[[Titanium]] |Ti | {| |'''+2'''||86 |- |'''+3'''||67 |- |'''+4'''||60.5 |} |- | 23 |[[Vanadium]] |V | {| |'''+2'''||64 |- | '''+4'''||58 |- |'''+5'''||54 |} |- | 24 |[[Chromium]] |Cr | {| |'''+2'''||73 ||''ls'' |- | '''+2'''||80 ||''hs'' |- | '''+3'''||61.5 |- | '''+4'''||55 |- | '''+5'''||49 |- | '''+6'''||44 |} |- | 25 |[[Manganese]] |Mn | {| |'''+2'''||67 |- |'''+3''' ||58 ||''ls'' |- |'''+3'''|| 64.5 ||''hs'' |- |'''+4''' || 53 |- |'''+5'''<sup>4</sup> ||33 |- |'''+6'''<sup>4</sup> ||25.5 |- |'''+7''' ||46 |} |- | 26 |[[Iron]] |Fe | {| |'''+2'''|| 61 ||''ls'' |- |'''+2''' ||78 ||''hs'' |- | '''+3'''|| 55 ||''ls'' |- |'''+3'''|| 64.5 ||''hs'' |- |'''+4'''||58.5 |- |'''+6'''<sup>4</sup> ||25 |} |- | 27 |[[Cobalt]] |Co | {| |'''+2'''||65 ||''ls'' |- |'''+2''' ||74.5 ||''hs'' |- |'''+3'''||54.5||''ls'' |- |'''+3'''||61||''hs'' |- |'''+4'''||53 |} |- | 28 |[[Nickel]] |Ni | {| |'''+2'''|| 69 |- |'''+3'''|| 56 ||''ls'' |- |'''+3'''|| 60 ||''hs'' |- |'''+4''' || 48 ||''ls'' |} |- | 29 |[[Copper]] |Cu | {| | '''+1''' || 77 |- |'''+2''' ||73 |- |'''+3'''||54 ||''ls'' |} |- | 30 |[[Zinc]] |Zn | {| | '''+2'''|| 74 |} |- | 31 |[[Gallium]] |Ga | {| | '''+3''' ||62 |} |- | 32 |[[Germanium]] |Ge | {| | '''+2'''|| 73 |- |'''+4''' || 53 |} |- | 33 |[[Arsenic]] |As | {| |'''+3'''|| 58 |- |'''+5'''|| 46 |} |- |34 |[[Selenium]] |Se | {| | '''<nowiki>&minus;</nowiki>2'''||align="right" width="50%"| 198 |- |'''+4'''|| align="right" width="50%"| 50 |- |'''+6'''|| align="right" width="50%"| 42 |} |- | 35 |[[Bromine ]] |Br | {| |'''<nowiki>&minus;</nowiki>1''' ||align="right" width="50%"|196 |- |'''+3'''<sup>4sq</sup>||align="right" width="50%"|59 |- |'''+5'''<sup>4</sup>|| align="right" width="50%"|31 |- |'''+7'''|| align="right" width="50%"|39 |} |- | 37 |[[Rubidium]] |Rb | {| |'''+1'''|| 152 |} |- | 38 |[[Strontium]] |Sr | {| |'''+2'''|| 118 |} |- | 39 |[[Yttrium]] |Y | {| |'''+3'''|| 90 |} |- | 40 |[[Zirconium]] |Zr | {| |'''+4'''|| 72 |} |- | 41 |[[Niobium]] |Nb | {| |'''+3''' || 72 |- |'''+4''' ||68 |- |'''+5''' ||64 |} |- | 42 |[[Molybdenum]] |Mo | {| | '''+3'''|| 69 |- |'''+4''' || 65 |- |'''+5'''||61 |- |'''+6'''|| 59 |} |- | 43 |[[Technetium]] |Tc | {| |'''+4'''|| 64.5 |- |'''+5'''|| 60 |- |'''+7'''|| 56 |} |- | 44 |[[Ruthenium]] |Ru | {| |'''+3'''|| 68 |- | '''+4'''||62 |- |'''+5'''|| 56.5 |- |'''+7'''<sup>4</sup>|| 38 |- |'''+8'''<sup>4</sup>|| 36 |} |- |45 |[[Rhodium]] | Rh | {| |'''+3'''|| 66.5 |- |'''+4'''|| 60 |- |'''+5'''|| 55 |} |- | 46 | [[Palladium]] | Pd | {| |'''+1'''<sup>2</sup>|| 59 |- |'''+2'''|| 86 |- |'''+3'''|| 76 |- |'''+4'''|| 61.5 |} |- | 47 | [[Silver]] | Ag | {| |'''+1'''||align="right" width="50%"| 115 |- |'''+2'''||align="right" width="50%"| 94 |- |'''+3'''||align="right" width="50%"| 75 |} |- | 48 | [[Cadmium]] | Cd | {| |'''+2'''|| 95 |} |- | 49 | [[Indium]] | In | {| |'''+3'''|| 80 |} |- | 50 | [[Tin]] | Sn | {| | '''+2'''||align="right" width="50%"|118 |- |'''+4''' ||align="right" width="50%"| 69 |} |- | 51 | [[Antimony]] | Sb | {| |'''+3'''|| 76 |- |'''+5'''|| 60 |} |- | 52 | [[Tellurium]] | Te | {| |'''<nowiki>&minus;</nowiki>2''' || align="right" width="50%"|221 |- |'''+4''' ||align="right" width="50%"| 97 |- |'''+6''' ||align="right" width="50%"|56 |} |- | 53 | [[Iodine]] | I | {| |'''<nowiki>&minus;</nowiki>1'''|| align="right" width="50%"|220 |- |'''+5'''|| align="right" width="50%"|95 |- |'''+7'''||align="right" width="50%"| 53 |} |- | 54 | [[Xenon]] | Xe | {| |'''+8''' || 48 |} |- | 55 | [[Caesium]] | Cs | {| | '''+1'''|| 167 |} |- | 56 | [[Barium]] | Ba | {| | '''+2''' || 135 |} |- | 57 | [[Lanthanum]] | La | {| | '''+3'''|| 103.2 |- |} |- | 58 | [[Cerium]] | Ce | {| |'''+3''' ||align="right" width="50%"| 102 |- |'''+4''' ||align="right" width="50%"| 87 |} |- | 59 | [[Praseodymium]] | Pr | {| |'''+3''' || 99 |- |'''+4''' || 85 |} |- | 60 | [[Neodymium]] | Nd | {| |'''+2'''<sup>8</sup> || 129 |- |'''+3''' || 98.3 |} |- | 61 | [[Promethium]] | Pm | {| |'''+3''' || 97 |} |- | 62 | [[Samarium]] | Sm | {| |'''+2'''<sup>4</sup> || 122 |- |'''+3''' || 95.8 |} |- | 63 | [[Europium]] | Eu | {| |'''+2''' || 117 |- |'''+3''' || 94.7 |} |- | 64 | [[Gadolinium]] | Gd | {| |'''+3''' || 93.8 |} |- | 65 | [[Terbium]] | Tb | {| |'''+3''' ||92.3 |- |'''+4''' || 76 |} |- | 66 | [[Dysprosium]] | Dy | {| |'''+2''' ||107 |- |'''+3'''|| 91.2 |} |- | 67 | [[Holmium]] | Ho | {| |'''+3'''||90.1 |} |- | 68 | [[Erbium]] | Er | {| |'''+3'''|| 89 |} |- | 69 | [[Thulium]] | Tm | {| |'''+2'''|| 103 |- |'''+3'''|| 88 |} |- | 70 | [[Ytterbium]] | Yb | {| |'''+2'''|| 102 |- |'''+3'''|| 86.8 |} |- | 71 | [[Lutetium]] | Lu | {| |'''+3'''|| 86.1 |} |- | 72 | [[Hafnium]] | Hf | {| |'''+3'''|| 71 |} |- | 73 | [[Tantalum]] | Ta | {| |'''+3'''|| 72 |- |'''+4'''||68 |- | '''+5'''||64 |} |- | 74 | [[Tungsten]] | W | {| |'''+4'''|| 66 |- |'''+5'''|| 62 |- |'''+6'''||60 |} |- | 75 | [[Rhenium]] | Re | {| |'''+4'''||63 |- |'''+5'''|| 58 |- |'''+6'''|| 55 |- |'''+7'''|| 53 |} |- | 76 | [[Osmium]] |Os | {| |'''+4'''|| 63 |- |'''+5'''|| 57.5 |- |'''+6'''|| 54.5 |- |'''+7'''|| 52.5 |- |'''+8'''<sup>4</sup>|| 39 |} |- | 77 | [[Iridium]] | Ir | {| |'''+3'''|| 68 |- |'''+4'''|| 62.5 |- |'''+5'''|| 57 |} |- | 78 | [[Platinum]] | Pt | {| |'''+2'''|| 86 |- |'''+4'''|| 62.5 |- |'''+5'''|| 57 |} |- | 79 | [[Gold]] | Au | {| |'''+1'''|| 137 |- |'''+3'''||align="right" width="50%"| 85 |- |'''+5'''||align="right" width="50%"| 57 |} |- | 80 | [[Mercury (element)|Mercury]] | Hg | {| |'''+1'''|| 119 |- |'''+2'''|| 102 |} |- | 81 | [[Thallium]] | Tl | {| | '''+1''' || 150 |- | '''+3''' || 88.5 |} |- | 82 | [[Lead]] | Pb | {| |'''+2'''|| 119 |- |'''+4'''|| 77.5 |} |- | 83 | [[Bismuth]] | Bi | {| |'''+3'''||align="right" width="50%"| 103 |- | '''+5'''||align="right" width="50%"| 76 |} |- | 84 | [[Polonium]] | Po | {| |'''+4'''|| 94 |- |'''+6'''|| 67 |} |- | 85 | [[Astatine]] | At | {| |'''+7'''|| 62 |} |- | 87 | [[Francium]] | Fr | {| |'''+1'''|| 180 |} |- | 88 | [[Radium]] | Ra | {| |'''+2'''<sup>8</sup>|| 148 |} |- | 89 |[[Actinium]] | Ac | {| |'''+3'''|| 112 |} |- | 90 | [[Thorium]] | Th | {| |'''+4'''|| 94 |} |- | 91 | [[Protactinium]] | Pa | {| | '''+3'''|| align="right" width="50%"| 104 |- | '''+4'''||align="right" width="50%"| 90 |- | '''+5'''||align="right" width="50%"| 78 |} |- | 92 | [[Uranium]] | U | {| | '''+3'''|| 102.5 |- | '''+4'''|| 89 |- | '''+5'''|| 78 |- | '''+6'''||73 |} |- | 93 | [[Neptunium]] | Np | {| |'''+2'''|| align="right" width="50%"|110 |- | '''+3'''||align="right" width="50%"| 101 |- | '''+4'''||align="right" width="50%"| 87 |- | '''+5'''||align="right" width="50%"| 75 |- | '''+6'''||align="right" width="50%"| 72 |- | '''+7'''||align="right" width="50%"|71 |} |- | 94 | [[Plutonium]] | Pu | {| |'''+3'''|| align="right" width="50%"|100 |- | '''+4'''||align="right" width="50%"|86 |- | '''+5'''||align="right" width="50%"|74 |- | '''+6'''||align="right" width="50%"|71 |} |- | 95 | [[Americium]] | Am | {| |'''+2'''<sup>8</sup>||126 |- | '''+3'''|| 97.5 |- | '''+4'''|| 85 |} |- | 96 | [[Curium]] | Cm | {| |'''+3'''|| 97 |- |'''+4'''|| 85 |} |- | 97 | [[Berkelium]] | Bk | {| |'''+3'''|| 96 |- |'''+4'''|| 83 |} |- | 98 | [[Californium]] | Cf | {| |'''+3'''|| 95 |- | '''+4'''|| 82.1 |} |} ==See also== *[[Atomic radii of the elements (data page)|Atomic radii of the elements]] == References == <references /> == External links == *[http://www.webelements.com/ WebElements] [[Category:Chemical properties]] [[ast:Radiu iónicu]] [[bs:Ionski radijus]] [[cs:Iontový poloměr]] [[de:Ionenradius]] [[es:Radio iónico]] [[eu:Erradio ioniko]] [[fr:Rayon ionique]] [[it:Raggio ionico]] [[nn:Ioneradius]] [[pl:Promień jonowy]] [[pt:Raio iônico]] [[ru:Ионный радиус]]