What is Atomic radii: Definition and 20 Discussions

The atomic radius of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Four widely used definitions of atomic radius are: Van der Waals radius, ionic radius, metallic radius and covalent radius. Typically, because of the difficulty to isolate atoms in order to measure their radii separately, atomic radius is measured in a bonded state; however theoretical calculations are of course simpler when considering atoms in isolation. The dependencies on environment, probe, and state lead to a multiplicity of definitions.
Depending on the definition, the term may apply to atoms in condensed matter, covalently bonding in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical models. The value of the radius may depend on the atom's state and context.Electrons do not have definite orbits nor sharply defined ranges. Rather, their positions must be described as probability distributions that taper off gradually as one moves away from the nucleus, without a sharp cutoff; these are referred to as atomic orbitals or electron clouds. Moreover, in condensed matter and molecules, the electron clouds of the atoms usually overlap to some extent, and some of the electrons may roam over a large region encompassing two or more atoms.
Under most definitions the radii of isolated neutral atoms range between 30 and 300 pm (trillionths of a meter), or between 0.3 and 3 ångströms. Therefore, the radius of an atom is more than 10,000 times the radius of its nucleus (1–10 fm), and less than 1/1000 of the wavelength of visible light (400–700 nm).

For many purposes, atoms can be modeled as spheres. This is only a crude approximation, but it can provide quantitative explanations and predictions for many phenomena, such as the density of liquids and solids, the diffusion of fluids through molecular sieves, the arrangement of atoms and ions in crystals, and the size and shape of molecules.

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  1. adf89812

    I can't apply my knowledge of shielding to explain the three slopes

    Also, why does red taper off slope towards the end of the subsequence, but green and purple never taper off in slope (flatten out)?
  2. Butch

    Atomic Radii Table | Element & Isotope Charge Radius

    I am doing some work on atomic structure. I have an app for referencing the charge radius of nuclei of elements and their isotopes, however I need a table that has the atomic radii of the elements and their isotopes.
  3. Bobs

    I'm getting two different answers for the atomic radius of iridium

    I'm getting too different answers for atomic radius of iridium. I've already found 1.34 x 10-8 but all shows different answers. I mean like 1.34, 1.35, 1.36... Are those correct?
  4. TheSodesa

    What Are the Ionic Radii of Mg2+ and O2- in MgO's Crystal Structure?

    Homework Statement Below is an image of a unit cell for MgO. Does MgO have the lattice structure of NaCl or ZnS? If the density of MgO, ##\rho## = 3,58g/cm3, evaluate the sizes of the radii of Mg2+- and O2--ions. Answers: 149pm and 62pm Homework EquationsThe Attempt at a Solution Looking...
  5. skepticwulf

    Why are Na atoms depicted smaller than Cl atoms in Chemistry books?

    Atomic radii of Na is much bigger than of Cl yet the drawings in Chemistry books often depict Na atoms smaller than Cl. Is there a reason for that??
  6. W

    Why does the atomic radii get smaller from the left to right?

    Why does the atomic radii get smaller from the left to right of a period but get bigger from top to bottom of a group? Wikipedia says in an article about electron shielding "Next we take Beryllium, Be as an example. It has 2 electrons in the 2s shell and thus, these electrons will repel each...
  7. P

    Atomic radii of transition elements

    Hi, my question is regarding atomic radii of transition elements. When we move to the right of the periodic table (in the region of the transition elements) the atomic number increases, thus there is one more proton in the nucleus and on more electron in the atom. The nuclear charge increases...
  8. K

    Atomic Radii Trends: Anion vs Periodic Table

    First, it says in my textbook that in an anion, the atomic size will be larger than that of the neutral atom. It says this is because the extra electrons causes more repulsion and then increases the atomic radius. In the next chapter, it says as you move across a period [from left to right] in...
  9. somasimple

    What are the common atomic radii used for chemical pictures?

    Hi all, What are the common atomic radii that are used for drawing chemical pictures? Is it the ionic or calculated or? Thanks.
  10. J

    Atomic Radii & Nuclear Charge: Exploring the Periodic Table

    How does atomic radii decrease when we move left to right in a periodic table? Though the nuclear charge increase as a result of increase in number of protons,the same increase is occurring in number of electrons.
  11. L

    Relative Atomic Radii (Atoms and Ions)

    Hi, How would you determine the relative atomic sizes of a neutral atom and an ion? I can't figure this out. It can't be that all neutral atoms are always smaller than all ions can it? For example, how would I determine if Cl- is smaller or larger than S?. (The answer is that Cl- is...
  12. D

    Atomic Radii of Fe and Ni: Which to Trust?

    for the calculations in one of my homework questions, i need to use the atomic radii of Fe and Ni, the problem is that every site i come across gives me different values Fe wikipedia 126pm physlink 1.72A chemicool 140pm how do i know which one to "trust" ?
  13. Saladsamurai

    How are atomic radii and H-bond strength related?

    I answered a question that my professor asked: "Why is the boiling point of HF much higher than that of HCl even though HCl has a larger molar mass?" The answer had to do with F being more electronegative than Cl and thus making stronger H-bonds. He also said on an aside that it all boils...
  14. S

    Explaining the Anomaly in Atomic Radii of Transition Metals

    Could anybody help me with this? The atomic radii of the transition metals show some anomaly in their atomic radii as compared to those elements in Group 1A-7A, which generally shows a decrease as one goes from left to right in a period. The atomic radii of the transition metals decrease as...
  15. R

    Comparing Atomic Radii: K+ vs Ar

    which atom has a larger atomic radius: K+ or Ar ?
  16. T

    What Went Wrong with My Calculation for Iridium Atomic Radii?

    hey just wondering where I went wrong Iridium Crystallizes in a face centred cubic unit call that has an edge length of 3.833A The atom in the cantre of the face is in contact with the corner atoms calculate the atomic radii of the irridium atom I did this using pythag...
  17. S

    Why is there a difference in atomic and ionic radii for Ca and Zn?

    hey guys! I was just wondering if anyone could help me out a bit on this. I have the following radii (in angstroms...not that it really matters) Ca: 1.74 Ca 2+: .99 Zn: 1.31 Zn 2+: .74 Does anyone have any idea why the difference between the atomic radii of the two elements is...
  18. E

    Determining Atomic Radii: Calculation and Method Explained

    [SOLVED] Atomic radii I need to know precisely how the average atomic radii are calculated or found? I would expect it to be on the average contents of an experimental sample with adjustment for differing percentages. This would mean that isotopes missing from the sample are not included in...
  19. E

    Understanding Atomic Radii: Average Figures or Unclear Measurement?

    Apologies for raising this question again, but it has finally dawned on me that as the Tables of Elements give an average mass (i.e. for all isotopes of each element) as the Relative Atomic Mass for that element; then my question is - Is the figure quoted for Atomic Radii also an average...
  20. E

    Discovering Atomic Radii for Isotopes: A Comprehensive Guide

    Can anyone tell me where to find Atomic Radii for Isotopes? (All the tables I have found so far only list atomic radii for the 92 elements shown on the main table.)