Section 6.3Practice & Assessment

Problems

16. Which has the largest atomic radius: Mg, Si, S, or Na? The smallest?

Largest is NaSmallest is S

17.The figure on the right shows helium, krypton, and radon. Which one is krypton? How can you tell?

B, the atomic radius increases when going down a group, so He is the smallest and radon is the biggest.

A B C

18. Can you determine which of the two unknown elements has the larger radius if the only known information is the atomic number of one of the elements is 20 greater than the other? Explain.

No, if all that is known is that the atomic number is one element is 20 greater than that of the other, then you will be unable to determine the specific groups and periods that the element are in. Without this information, you cannot apply the periodic trends in atomic size to determine which element has the larger radius.

19. Determine which element in each pair has the largest atomic radius:a. the element in period 2, group 1; or the element in period 3, group 18b. the element in period 5, group 2; or the element in period 3, group 16c. the element in period 3, group 14; or the element in period 6, group 15d. the element in period 4, group 18; or the element in period 2, group 16

A. element in period 2, group 1

B. element in period 5, group 2

• C. element in period 6, group 15

• D. element in period 4, group 18

20. Explain how the period and group trend in atomic radii are related to electron configuration.

Atomic radii increase down a group as electron are added to higher energy levels and inner core electrons shield the valence electron from the increased nuclear charge. Atomic radii decrease across a period as increased nuclear charge coupled with unchanging shielding by inner core electrons pulls the valence electrons closer to electrons.

21. Indicate whether F or Br has a larger value for each of the following properties:a. electronegativity b. ionic radiusc. atomic radius d.ionization energy

A. FB. BrC. BrD. F

22. Explain why it takes more energy to remove the 2nd electron from a lithium atom than it does to remove a 4th electron from a carbon atom?

Li’s 2nd removed electron is an inner core electron not a valence electron. C’s 4th removed electron is still a valence electron.

23. Determine the differences in electronegativity, ionic radius, atomic radius, and 1st ionization energy for oxygen and beryllium.

∆Electronegativity 1.87 ∆ Ionic radius 109 pm ∆ Atomic radius 39 pm ∆ 1st ionization energy 410 kJ/mol]

24. Graph the atomic radii of the representative elements in periods 2,3, and 4 versus their atomic numbers. Connect the points of elements in each period, so that there are 3 separate curves on the graph. Summarize the trend in atomic a radii shown on your graph. Explain

In general, atomic radii decrease across a period due to increased nuclear charge (while e- remain at ~ avg energy);

they increase down a group due to valence electrons placed in larger orbitals belonging to higher principal levels.