Size of protactinium in several environments

One measure of size is the element-element distance within the element. It is not always easy to make sensible comparisons between the elements however as some bonds are quite short because of multiple bonding (for instance the O=O distance in O2 is short because of the the double bond connecting the two atoms. The bond length in PaPa is: 321.2 pm.

There are several other ways ways to define radius for atoms and ions. Follow the appropriate hyperlinks for literature references and definitions of each type of radius. All values of radii are given in picometres (pm). Conversion factors are:

  • 1 pm = 1 x 10-12 metre (meter)
  • 100 pm = 1 Ångstrom
  • 1000 pm = 1 nanometre (nm, nanometer)

Neutral radii

The size of neutral atoms depends upon the way in which the measurement is made and the environment. Follow the appropriate hyperlinks for definitions of each radius type. The term "atomic radius" is not particularly helpful although its use is widespread. The problem is its meaning, which is clearly very different in different sources and books. Two values are given here, one is based upon calculations and the other upon observation - follow the appropriate link for further details.

Ionic radii

This table gives some ionic radii. In this table, geometry refers to the arrangment of the ion's nearest neighbours. Size does depend upon geometry and environment. For electronic configurations, where it matters, the values given for octahedral species are low spin unless stated to be high spin. The terms low spin and high spin refer to the electronic configurations of particular geomtries of certain d-block metal ions. Further information is available in inorganic chemistry textbooks, usually at Level 1 or First Year University level. For definitions of ionic radius and further information, follow the hypertext link.

Ion Coordination type Radius / pm
Pa(III)6-coordinate, octahedral 118
Pa(IV)6-coordinate, octahedral 104
Pa(V)Ionic radius for octahedral +5 ions of the chemical elements displayed on a miniature periodic table 6-coordinate, octahedral 92
Pa(IV)Ionic radius for 8-coordinate +4 ions of the chemical elements displayed on a miniature periodic table 8-coordinate 115
Pa(V)Ionic radius for 8-coordinate +5 ions of the chemical elements displayed on a miniature periodic table 8-coordinate 105

Pauling ionic radius of the chemical elements displayed on a miniature periodic tablePauling ionic radii

This table shows Pauling radii for protactinium
Ion Pauling radius / pm
Pauling radius for +1 ions of the chemical elements displayed on a miniature periodic table Pa(I) no information

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protactinium atomic number