Periodic Trends: Atomic Radius

Atomic radius represents the distance from the nucleus to the outer shell of an element. 

Trends in Atomic Radius

Concept: Understanding Atomic Radius

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Video Transcript

In this new video, we're going to take a look at atomic radius. Now we're going to say atomic radius is defined as half the distance between the nuclei in a molecule of two identical elements.
What does that mean? Well, remember we know that we have an element which is represented by a sphere. The diameter would just be the distance all the way across. The radius is just half of that, so our atomic radius is just that. And now if we are dealing a diatomic molecule we’d say that the sum of the radii equals the total distance between their two nuclei. That's what that definition is basically saying.
Now we're going to say it's important to remember the trend for atomic radius. So we’re going use this representation of the periodic table. So, the best strategy here is just to make a sheet with all the trends because there are tons of different types of periodic trends that you need to remember one can be atomic radius. So we're going to say generally, atomic radius will decrease as we go from left to right across a period. So it decreases going this way, and we going to say generally, it going to increase going down any group. So we going to say it increases going down this way. So just remember that trend in terms of atomic radii. 

For a diatomic molecule, atomic radius is defined as half the distance between the nuclei in a molecule of two identical elements.

Example: If the sum of the atomic radii of diatomic carbon is 154 pm and of diatomic chlorine is 198 pm, what is the sum of the atomic radii between a carbon and a chlorine atom. 

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Problem: Which one of the following atoms has the largest atomic radius?

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Periodic Trends: Atomic Radius Additional Practice Problems

Which of these atoms has the smallest radius? 

(a) Al 

(B) P 

(C) As 

(D) Te 

(E) Na

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The atomic radius of bromine is larger than the atomic radius of _____.

a. chlorine

b. uranium

c. potassium

d. iodine

e. xenon 

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Of the following species, __________ has the largest radius.

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Rank the following atoms according to size: As, Cl, Se, F

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How do atomic properties account for the low densities of the Group 1A(1) elements?

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Lithium salts are often much less soluble in water than the corresponding salts of other alkali metals. For example, at 18°C, the concentration of a saturated LiF solution is 1.0×10–2 M, whereas that of a saturated KF solution is 1.6 M. How would you explain this behavior?

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Which alkaline earth metal has the smallest atomic radius?

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Rank these ions by their expected hydration energy.

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Rank the following elements in order of decreasing atomic radius. Rank from largest to smallest radius. To rank items as equivalent, overlap them.

a) Rb, Na, K, Li

b) Li, Be, B, N

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Rank the following elements in order of decreasing atomic radius. Rank from largest to smallest radius. To rank items as equivalent, overlap them.

F, C, O, B

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Which of the following correctly lists the five atoms in order of decreasing size (largest to smallest)?

             Ca,       K,       Ne,         O,         P

a) P > Ne > Ca > K >O

b) O > Ca > K > P > Ne

c) F > O > P > Ca > K

d) K > Ca > P > O > Ne

e) Ca > P > O > Ne > K

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Which atom below has the largest atomic radius?

A. Li

B. N

C. Na

D. S

E. Cl

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Of the following, which gives the correct order for atomic radius for Mg. Na, P. Si and Ar?

A) Mg>Na> P> Si> Ar

B) Ar> Si> P > Na > Mg

C) Si> P> Ar>Na > Mg

D) Na > Mg> Si> P> Ar

E) Ar> P> Si > Mg>Na

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Place the following atoms in order of increasing atomic radii (smallest to largest):

S, Cl, Se, and As.

a. Cl < S < Se < As

b. S < Cl < As < Se

c. S < Cl < Se < As

d. As < Se < S < Cl

e. Se < As < S < Cl

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The atomic radius of main-group elements generally decreases from left to right across a row (or period), because the __________.        

A. effective nuclear charge decreases

B. principal quantum number of the valence orbitals increases

C. number of core electrons increases

D. effective nuclear charge increases

E. principal quantum number of the valence orbitals decreases

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Which is the larger species in each pair?

a. Sr or Sr2+ 

b. N or N3-

c. Ni or Ni2+

d. S2- or Ca2+

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In moving from top to bottom in the same column on the periodic table, what trend is expected for atomic size and why?

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

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In which group do the atoms become larger in going down the group?

a) group 1A

b) group 4A

c) group 5A

d) group 7A

e) groups 1A, 4A, 5A, and 7A

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Which of these atoms will be the  smallest ?

a) Si (Z = 14)

b) P (Z = 15)

c) Ge (Z = 32)

d) As (Z = 33)

 

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Which of these elements has the  smallest  atomic radius?

a) fluorine

b) chlorine

c) bromine

d) iodine

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The size of metal atoms

a) generally increases progressively from top to bottom in a group in the periodic table.

b) generally increases progressively from left to right in a period.

c) are smaller than those of the corresponding ions.

d) do not change upon losing electrons.

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Which one of the following elements would be expected to have the  largest atomic radius? 

a) Li

b) Cs

c) F

d) Br

e) I

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For the following sets of atoms, write an “L” above the one that is largest, and an “S” above the one that is smallest

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Circle the largest atom:

Cl    

P

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In general, atomic size tends to increase

1. from top to bottom and from left to right on the periodic table.

2. from bottom to top and from right to left on the periodic table.

3. There is no relationship between the size of an atom and its position on the periodic table.

4. from bottom to top and from left to right on the periodic table.

5. from top to bottom and from right to left on the periodic table. 

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The atomic radius of main-group elements generally increases down a column because __________.

A. effective nuclear charge decreases down a column

B. the mass of an atom increases down a column

C. the highest principal quantum number of the valence orbitals increases

D. effective nuclear charge increases down a column

E. both effective nuclear charge increases down a column and the principal quantum number of the valence orbitals increases

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Consider the following atoms: Br, Sn, Sb, Te, I. What has the largest atomic radius?

a. Br

b. Sn

c. Sb

d. Te

e. I

Which is the most paramagnetic?

a. Br

b. Sn

c. Sb

d. Te

e. I

What has the largest ionization energy?

a. Br

b. Sn

c. Sb

d. Te

e. I

Which has the largest electronegativity?

a. Br

b. Sn

c. Sb

d. Te

e. I

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Place the following in order of decreasing atomic radius.

              As              S                F

 

A. As > F > S

B. S > As > F

C. F > As > S

D. As > S > F

E. S > F > As

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Consider the following radii:

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