What is the difference between the ionic radius and the atomic radius of an element? | Socratic
One such trend is closely linked to atomic radii -- ionic radii. Neutral atoms tend to increase in size down a group and decrease across a period. Relationship between Atomic and Ionic Radii. G. R. SOMAYAJULU AND SANTI R. PALIT. Indian Association for the Cultivation of Science, Calcutta 32, India. The ionic radius is the radius of an atom forming ionic bond or an ion. The radius of each atom in an ionic bond will be different than.
It will also decrease because there are now less electrons in the outer shell, which will decrease the radius size. An analogy to this can be of a magnet and a metallic object.
If ten magnets and ten metallic objects represent a neutral atom where the magnets are protons and the metallic objects are electrons, then removing one metallic object, which is like removing an electron, will cause the magnet to pull the metallic objects closer because of a decrease in number of the metallic objects.
This can similarly be said about the protons pulling the electrons closer to the nucleus, which as a result decreases atomic size. The ionic radius decreases for the generation of positive ions. This can be seen in the Figure 4 below. The gain of an electron adds more electrons to the outermost shell which increases the radius because there are now more electrons further away from the nucleus and there are more electrons to pull towards the nucleus so the pull becomes slightly weaker than of the neutral atom and causes an increase in atomic radius.
The ionic radius increases for the generation of negative ions. Metallic Radius The metallic radius is the radius of an atom joined by metallic bond. The metallic radius is half of the total distance between the nuclei of two adjacent atoms in a metallic cluster. Metallic radii from metallic bonding Periodic Trends of Atomic Radius An atom gets larger as the number of electronic shells increase; therefore the radius of atoms increases as you go down a certain group in the periodic table of elements.
Periodic Trend in atomic radii Vertical Trend The radius of atoms increases as you go down a certain group. Because the electrons added in the transition elements are added in the inner electron shell and at the same time, the outer shell remains constant, the nucleus attracts the electrons inward.
The electron configuration of the transition metals explains this phenomenon.
Atomic Radii - Chemistry LibreTexts
This is why Ga is the same size as its preceding atom and why Sb is slightly bigger than Sn. Herring, and Jeffry D. Pearsin Prentice Hall, Problems Which atom is larger: Which atom is larger: Which atom is smaller: Put in order of largest to smallest: F, Ar, Sr, Cs. Which has a bigger atomic radius: If Br has an ionic radius of pm and the total distance between K and Br in KBr is pm, then what is the ionic radius of K? Which has a smaller atomic radius: If the distance between the nuclei of two atoms in a metallic bond is pm, what is the atomic radius of one atom?
If Z effective is increasing, is the atomic radius also increasing? Also remember the trend for the atomic radii.
Periodic Trends in Ionic Radii - Chemistry LibreTexts
Now, you might think that outer shell electrons could shield, too. So you might think that oh, this electron right here in magenta could shield the other electron in magenta.
But the problem is they're both at pretty much the same distance from the nucleus, so outer shell electrons don't really shield each other. It's more of these inner shell electrons. And because you have the same number of inner shell electrons shielding as in the lithium example-- so let me go ahead and highlight those again. So we have two inner shell electrons shielding a beryllium. We also have two inner shell electrons shielding in lithium.
Because you have the same number of shielding but you have a higher positive charge, those outer electrons are going to feel more of a pull from the nucleus. And they're going to be pulled in even tighter than you might imagine, or at least tighter than our previous example.
So these electrons are pulled in even more. And because of that, you're going to get the beryllium atom as being smaller than the lithium atom, hence the trend. Hence as you go across the period, you're always going to increase in the number of protons and that increased whole is going to pull those outer electrons in closer, therefore decreasing the size of the atom. Let's look at ionic radius now.
And ionic radius can be kind of complicated depending on what chemistry you are involved in. So this is going to be just a real simple version.
If I took a neutral lithium atom again, so lithium-- so we've drawn this several times. Let me go ahead and draw it once more. So we have our lithium nucleus, which we have three electrons.
So once again I'll go ahead and sketch in our three electrons real fast. Two electrons in the inner shell, and one electron in the outer shell like that. And let's say you were going to form a cation, so we are going to take away an electron from our neutral atom. So we have-- let me go ahead and draw this in here-- we had a three protons in the nucleus and three electrons those cancel each other out to be a neutral atom.
What is the difference between the ionic radius and the atomic radius of an element?
And if we were to take away one of those electrons, so let's go ahead and show lithium losing an electron. So if lithium loses an electron, it's going to lose that outer electron. So the nucleus still has a plus 3 charge, because it has three protons in it.
And we still have our two inner shell electrons like that, but we took away that outer shell electron.
So we took away this electron in magenta, so let me go ahead and label this. So we lost an electron, so that's this electron right here, and so you could just show it over here like that. And by doing so, now we have three positive charges in our nucleus and only two electrons.
And so therefore our lithium gets a plus 1 charge. So it's Li plus, it's a cation. And so we formed a cation, which is smaller than the neutral atom itself. And that just makes intuitive sense. If you take away this outer electron, now you have three positive charges in the nucleus and only two electrons here.
So it's pulling those electrons in, you lost that outer electron, it's getting smaller.
- What is the relationship between atomic radius and ionization energy?
- Periodic Trends in Ionic Radii
- Atomic Radii
And so the cation is smaller than the neutralize atom. And so we've seen that neutral atoms will shrink when you convert them to cations, so it kind of makes sense that if you take a neutral atom and add an electron, it's going to get larger.
And so that's our next concept here. So if we took something like chlorine, so a neutral chlorine atom, and we added an electron to chlorine, that would give it a negative charge. So we would get chlorine with a negative charge, or the chloride anion, I should say. And so in terms of sizes, let's go ahead and draw a representative atom here. So if this is our neutral chlorine atom and we add an electron to it, it actually gets a lot bigger. So the anion is bigger than the neutral atom.
And let's see if we can think about why here. So if we were to draw an electron configuration, or to write a noble gas electron configuration for the neutral chlorine-- so you should already know how to do this-- you would just write your noble gas in brackets.
So neon and then 3s2, 3p5, so seven electrons in the outer shell for the neutral chlorine atom. For the chloride anion, you would start off the same way. You would say neon in brackets, 3s2. And you'd be adding an electron to it. So it wouldn't be 3p5, it would be 3p6 like that. And so now we would have so this would give us eight electrons in our outer shell, and this would give us only seven electrons in our outer shell.
Now, the explanation for the larger size of the chloride anion in most textbooks is, you'll see people say that the addition of this extra electron here, so that means that those electrons are going to repel each other more. You have eight of them instead of seven, and so because they repel each other more, it gets a little bit bigger. And that makes sense, but you'll see some people disagree with that explanation, and I haven't really seen a great alternative offered.
Difference Between Atomic Radius and Ionic Radius
And so however you want to think about it, generally the anion is larger than the neutral atom. But in terms of the explanation for that, you could think about it as electrons are repelling each other if you wanted to, despite the fact that people disagree with that. You could think about just more stuff as a really simple way of thinking about it. But again, in general for exams, think about the anion being larger.