The atomic radius of an element is the distance from its nucleus to its outer electron shell.
Atomic Radius
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Periodic Trend: Atomic Radius
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So Atomic radius is the distance between Adams nucleus and its outer electron shell, otherwise known as its valence shell. So here, if we take a look, we have our nucleus in the middle. And here we have our outer shell. The distance between the nucleus and the outer shell is our atomic radius. R. Now remember, within the nucleus we have our protons and neutrons are protons are positively charged particles. Neutrons are neutral and the nucleus itself contains our proton and our neutron. Now we're gonna say, here, going down a group, we're going to say that the number of electrons increases because our shells get larger and larger and they can hold more and more electrons. And we're gonna say that the number of electron shells also increase. But we're going to say, moving across the period. Though we're going to say that the number of electrons with within the same shell also will increase. We're gonna say increasing the number of shell electrons in the same shell causes greater attraction with the nucleus. And what this does is it causes a slight decrease in our atomic radius. So we have these two forces at work. We're adding more electrons, and as a result our Adam gets larger and larger with more and more shelves. But as we add more and more shells, there's gonna be more electrons found within each of those shelves. This is going to cause some issues with our atomic radius, so there's an increase in a decrease type of phenomenon happening here with the increase of the number of electrons. The overall periodic trend is that as we move from left to right, so remember, we're always heading towards the top right corner of the periodic table. Are atomic radius will decrease? So click on to the next video and let's take a look at what this periodic table would look look like in terms of atomic radius.
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Periodic Trend: Atomic Radius
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So remember we said the general trend is as we had from left to right and up a group are atomic radius will decrease. So remember, as we had up a group, we say that the number of shells is going to decrease, so this causes a decrease in my atomic radius at the same time as removing from left to right of the periodic table. We're going to say that the shell number stays constant, but the number of electrons within that shell is increasing. This causes greater attraction to the nucleus which compresses the atomic radius a bit. So if we take a look here, we can see that typically we have our atomic radius given to us within PICO meters. We can see that hydrogen is pretty small at 37 PICO meters and we can see that as we head from hydrogen to helium, there's a small decrease. Now off course, there's gonna be exceptions here and there. Ah, lot of them happen within the pit here with our transition. Metals also realized that the last world, the periodic table, those elements because they're so large and so heavy because they've been synthesized in laboratories. There a little bit unstable, so we don't have definitive information on terms of their atomic radius. So we just leave them out and realize that we have our other transition metals that are below this, our inner transition metals. They have the same issue. So when it comes to atomic radius, these are the ones that are most important. You're not expected to memorize these numbers, so don't worry. You just need to understand the general trend. And it is as we head towards the top right corner of the periodic table. Atomic Radius, for the most part, will decrease. So keep that in mind when looking at questions dealing with atomic radius.
Moving towards the top right corner of the Periodic Table causes the atomic radii to decrease.
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Periodic Trend: Atomic Radius Example 1
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So here it says which of the following Adams has the largest atomic radius. So here we're looking at K R. B. Why s r and CIA? So to make a little bit harder, I removed the values. Now you can go and take a look, but just rely on the general trend. We said as you had towards the top right corner, your atomic radio should decrease. But here we're looking for the largest atomic radius, so they could think of it in the opposite way. Who's the furthest from the top right corner? The answer would be RB R B would be the one here with the largest atomic radius based on. The choice is given to us. So just remember that general trend it would be larger than all of the others presented before us.
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Problem
Arrange the following atoms in order of decreasing atomic radius:Sr, Se, Ne, Zn
A
Sr > Zn > Se > Ne
B
Zn > Sr > Se > Ne
C
Ne > Sr > Zn > Se
D
Zn > Se > Sr > Ne
E
Se > Sr > Zn > Ne
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Problem
Which alkaline earth metal has the smallest atomic radius?
A
Ca
B
Rb
C
Na
D
Ra
E
Fr
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Problem
In moving from top to bottom in the same column on the periodic table, what trend is expected for atomic size?
A
Increase because the nucleus is getting stronger.
B
Increase because electrons are being placed in higher n-values.
C
Decrease because the nucleus is getting stronger.
D
Increase because electrons are being added to degenerate orbitals.
E
Decrease because electrons are being placed in higher n-values.
Additional resources for Periodic Trend: Atomic Radius
PRACTICE PROBLEMS AND ACTIVITIES (24)
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- Which quantity must be determined experimentally in order to determine the bonding atomic radius of an atom? (...
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- Tungsten has the highest melting point of any metal in the periodic table: 3422 °C. The distance between W ato...
- Which of the following statements about the bonding atomic radii in Figure 7.7 is incorrect? (i) For a given p...
- The experimental Pb¬Cl bond length in lead(II)chloride, PbCl2, is 244 pm. Based on this value and data in Fig...
- Using only the periodic table, arrange each set of atoms in order from largest to smallest: (c) C, Cl, Cu.
- Using only the periodic table, arrange each set of atoms in order of increasing radius: (b) S, Si, Sr
- Which of the following three spheres represents a Ca atom, which an Sr atom, and which a Br atom?
- Consider S, Cl, and K and their most common ions. (a) List the atoms in order of increasing size.
- Choose the larger atom in each pair. a. Al or In b. Si or N c. P or Pb d. Si or Cl
- Choose the larger atom in each pair. a. Sn or Si b. Br or Ga c. Sn or Bi d. Se or Sn
- In Table 7.8, the bonding atomic radius of neon is listed as 58 pm, whereas that for xenon is listed as 140 pm...
- The following observations are made about two hypothetical elements A and B: The A¬A and B¬B bond lengths in t...
- Note from the following table that there is a significant increase in atomic radius upon moving from Y to La, ...
- Which of the following pairs of elements would you expect to have the most similar atomic radii? a. Si and Ga...
- The elements with atomic numbers 35 and 53 have similar chemical properties. Based on their electronic config...
- Consider the elements: Na, Mg, Al, Si, P. b. Which element has the smallest atomic radius?
- Why do atomic radii decrease from left to right across a period of the periodic table?
- Order the following atoms according to increasing atomic radius: S, F, O.
- Order the following atoms according to increasing atomic radius: Rb, Cl, As, K.
- Which atom in each of the following pairs has a larger radius? (a) Na or K (b) V or Ta (c) V or Zn (d) Li or B...
- Which atom in each of the following pairs has a larger radius? (a) C or Ge (b) Ni or Pt (c) Sn or I (d) Na or ...