Questions tagged [atomic-radius]

For questions about the atomic radius - a measure of the size of an atom, usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding "cloud" of electrons.

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22k views

How can we measure the atomic radius of an atom?

The definition of atomic radius is half the average internuclear distance of an atom. But many times I've been told that it is not possible to handle a single atom. Thus how can we measure the ...
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Finding orbit radius using the Bohr model and Rydberg equation

To start with its a homework problem, quite lengthy. A particle of mass equal to 208 times the mass of an electron moves in a circular orbit around a nucleus of charge $+3e$. Assuming the Bohr ...
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Which element has larger atomic radius — beryllium or xenon?

I say that xenon radius is smaller comparing to beryllium, but my friend says otherwise. What I think is that xenon is down in periodic table comparing to beryllium (3 periods down) and it's far ...
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1answer
112 views

Acid-base chemistry - determining stability [closed]

I am learning about acid-base reactions and how to identify whether an acid is strong or not by looking at the conjugate base. The more stable a conjugate base the stronger the acid. However, two of ...
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873 views

How to know which ionic compound have the highest lattice energy without knowing the values of the radii?

Given two ionic compounds, for instance: $$\ce{CaS} \quad \mathrm{or} \quad \ce{KCl}$$ What is the procedure to predict which of the two have the highest lattice energy (in absolute value)? (...
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Van der Waals Radius clarifications

I just read about van der Waals radius and had some questions about it. Would it be correct to say that in general, van der Waals radius decreases as we move from left to right in the periodic table? ...
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2answers
10k views

Why the radius of noble gases is more than the halogens or the previous groups?

Noble gases have a larger radius than the halogens. Sometimes it is greater than the radius of group I elements. Why it is like that? When we talk about radius of noble gases what type of radius ...
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1answer
327 views

Why is the distance between the atoms shorter in the dicarbon anion compared to the cation?

In general, the anions have bigger ionic radii than their corresponding neutral atoms, and the cations have smaller ionic radii then their corresponding neutral atoms. How come that does not apply to $...
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1answer
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Comparing radii in lithium, beryllium, magnesium, aluminium and sodium ions

Apparently the of last four, $\ce{Mg^2+}$ is closest in radius to $\ce{Li+}$. Is this true, and if so, why would a whole larger shell ($\ce{Mg^2+}$) be closer in radius to $\ce{Li+}$ than its ...
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Ionic radius of Al[3+] compared to K[+], Ca[2+], S[2-], and Cl[-]

I came across this question: Which of the following is bigger? $$\ce{K+, Ca^2+, Al^3+, S^2-, Cl-}$$ Now, I know that the radius decreases as the period progresses to the right and increases ...
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946 views

Why are there drastic changes sometimes in radius of isoelectronic ions?

$\ce{S^{2-}}$, $\ce{Cl-}$, $\ce{K+}$, and $\ce{Ca^{2+}}$ each have the same number of electrons. Their effective ionic radii are 182, 181, 138, and 100 picometers, respectively, and the number of ...
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897 views

How to list elements according to their radius? For example Ag, Cd, Au Can you check the accuracy of these sentences I've created?

I've asked a similar question before, but now I want to find out the real rule. Pleas tell me if my interpretation is correct: Cd, Ag , Au (increasing ray order). This happens because although we know ...
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1answer
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“Crystal radius” vs “Ionic radius”

What is the difference between crystal radius and ionic radius? For $\ce{NaCl}$ for example the ions combine to a crystal, and I would have guessed they are equal. But I then found an example of data, ...
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1answer
875 views

Predict the order of ionic radius

We have arrange the followig sequence for decreasing order of ionic radius . $Se^{-2},I^-,Br^{-},O^{-2},F^{-}$ In my book the answer given as $I^{-},Se^{-2},Br^{-},O^{-2},F^{-}$ But according to ...
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Newer ionic radii data than Shannon's 1976 compilation?

Shannon, R. D., 1976, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides: Acta Crystallographica Section A, v. 32, p. 751–767. DOI: 10.1107/...
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How/where can I find a reliable atomic radii table?

I am currently working on a periodic table to include it in a experimental chemistry book and I would like to include non-bonded atomic radii data so it would be easier for the students to learn about ...
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153 views

Why does being “bonded” decrease atomic size?

I have a furiously overwhelming question- Why is the atomic size of noble gases larger than the atomic size of the previous halogen when atomic sizes decrease across a group? I did search it on ...
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7k views

Why isn't the ionic radius of Mg2+ bigger than F-? [closed]

They will both have the same number of valence electrons, but $\ce{F-}$ is more electronegative. Why is it not the case that $\ce{Mg^2+}$ has a bigger radius than $\ce{F-}$?
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1answer
316 views

Bohr Radius Confusion

I saw online that the radius for each level is defined by the formula: $$r_n=n^2 r_1$$ Where $r_1$ is approximately $53\ \mathrm{pm}$. However, on the Barron's AP chemistry book 7th edition, it ...
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Why do atoms get smaller moving left to right on a periodic table? [duplicate]

I get that it's because of the increase number of protons, but I still don't understand the concept. When you move left to right on a periodic table, the protons increase at the same rate as the ...
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1answer
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Why is the radius of the caesium cation smaller than that of the chloride anion?

I am currently studying the structures of ionic compounds and how we can use radius ratios to predict the possible arrangement of ions in the lattice. My book mentions that the cation to anion radius ...
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Trend in atomic radius for noble gases

In an exam, we were given the following graph and asked to explain why the slope of the change in r vs. Z changes dramatically at a point along the curve. I understand that the d block causes the ...
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van der Waals coefficients for helium and neon

The values of the coefficient $b$ for helium and neon are $$\begin{array}{cc} \hline \text{Element} & b\text{ / }\mathrm{dm^3\ mol^{-1}} \\ \hline \ce{He} & 2.38 \times 10^{-2} \\ \ce{Ne} &...
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Why is the ionic radius of Al(3+) smaller than that of Li+?

I was examining the ionic radii of some ions from this site for a school assignment. I noticed a weird anomaly in the ionic radius of $\ce{Li+}$ as compared to that of $\ce{Al}^{3+}$. The ionic ...
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1answer
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Range of distance for Van der Waals force

Is there any range of distance between the nuclei of the atoms (in Angstrom, say between 4 to 12 Angstrom) within which there will be an occurrence of Van der Waals force (attraction) between them? ...
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Co vs Rh atomic radius

Why is the empirical atomic radius for both Co and Rh 135 pm, the same? Source
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441 views

The ionic radius of aluminium(III) vs. the covalent radius of neon?

I was wondering if it is a valid comparison to look at the ionic radius (noble-gas-like configuration) of a metal and the covalent radius of a noble gas. Specifically, $\ce{Al^{3+}}$ and $\ce{Ne}$. ...
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1answer
971 views

Why is it easier to determine the radius of inert/noble gases?

My textbook says it is possible to determine the atomic radius of the inert gases like He, Ne, Ar etc because they roam freely and are incapable of forming bonds. However it is very difficult to find ...
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1answer
4k views

Ionization energy and Electron Affnity

Which of the following statements correctly interprets the relationship between ionization energy, atomic radius Electron affinity when comparing two atoms. The correct choice as per my instructor ...
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1answer
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Ca and Mg hydrated radius in clay flocculation

Ca has an atomic radius of $197\mathrm{~pm}$ and a Pauling electronegativity of $1.00$. Mg has an atomic radius of $197\mathrm{~pm}$ and a Pauling electronegativity of $1.31$. Since Mg is smaller ...
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1answer
330 views

Meaning of the 1s orbital diagram

I'm a little confused about the interpretation of the 1s orbital diagram. I know that the outer boundary is where the wave function of the 1s orbital has a constant value, which means means there's a ...
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Why do some elements such as polonium not follow the trend of decreasing atomic radius?

Most of the periodic table follows the trend of increasing radius as you move down a family and decreasing radius as you move across a period. Why is this trend not observed for polonium?
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How would I find an apporpriate dopant element for a lattice

I am trying to figure how would I go about finding a dopant element that would fit in a copper lattice? I already have the data for the atomic dimensions and structure (available below), however how ...
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2answers
322 views

Interaction radius of a molecule

What is the most commonly used radius of an atom or molecule to describe the area that must touch another area of another molecule for the two to react. Is there one radius that always works or does ...
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1answer
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Comparison of atomic radii

My teacher told me that Neon has a larger atomic radius than Fluorine.I am of the understanding that it is merely a consequence of the way we define the atomic radius and that we use Van der walls ...
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1answer
1k views

The explanation on atomic size

I always receive two type of explanation for the decreasement of atomic size for elements across the period. Explanation according to proton number This explanation is from my teacher. The proton ...
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0answers
919 views

How to determine relative size of polyatomic ions?

How would you determine the size of a polyatomic ion? For example when determining which ion is bigger, $\ce{NH2-}$ or $\ce{I-}$, what would you use to determine the size difference? I know that $\...
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1answer
126 views

Atomic number $Z$

If electrons were spin-$\frac {3}{2}$ instead of spin-$\frac {1}{2}$ , what would be the atomic number $Z$ for the first noble gas ?
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409 views

What radius best represents reaction distance?

Molecules must be within a certain distance for a reaction to begin as well as satisfying a myriad of other factors. Whilst the exact distance varies from reaction to reaction, is their any distance/...
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1answer
403 views

Why does the “gap” between atomic radii get smaller down the periodic table?

The question asks: why is the difference in atomic radii between $\ce{K}$ and $\ce{Na}$ larger than the difference in atomic radii between $\ce{Cs}$ and $\ce{Rb}$? I do have some kind of notion that ...
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3answers
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Why does Mg2+ have the ionic radii bigger than Ca2+

If they were atoms, $\ce{Mg}$ should have a smaller radii. How does this change?
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1answer
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Is it possible to calculate atomic radius with electron configuration?

I need to know whether is it possible to calculate the atomic radius according to the number of electrons and electron configuration. Or is there any way to calculate the atomic radius using common ...
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2answers
325 views

XRD-Shorter distance between planes than actual radius of atoms/or cell parameter

I'm solving problems related to X-ray diffraction, and I get these results which apparently are correct. My question may be dumb, but I just can't see how the interplanar distance might be shorter ...
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Which is the bigger ion, F- or O-?

Well, according to the proton-electron ratio $\ce{O-}$ should be bigger than $\ce{F-}$ What about the charge/electron density in $\ce{F}$? Will it not affect the size of the atom of $\ce{F-}$?
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Can ionic and atomic radii be compared?

Can ionic and atomic radii be compared? For example, this is a common problem in some intro chem courses: Rank the following from smallest to largest: sodium ion, magnesium ion, neon, fluoride, ...
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For which pair of species is the difference in radii the greatest?

For which pair of species is the difference in radii the greatest? (A) $\ce{Li}$ and $\ce{F}$ (B) $\ce{Li+}$ and $\ce{F^-}$ (C) $\ce{Li+}$ and $\ce{O^2-}$ (D) $\ce{O^2-}$ and ...
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1answer
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How do we know the size of atoms in body centered cubic system?

I'm told that in the normal cubic system there are $\frac18$ of an atom at each corner and these atoms' radius are such that $a = 2r$ ($a$ is the lattice constant, $r$ radius of an atom). In bbc (...