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Sample Answers
1.
a. Atomic radius decreases from left to right across a period because of an increase in the nuclear charge.
b. Atomic radius increases from top to bottom down a group because of a greater number of principal
energy levels.
2.
a. Ionization energy increases from left to right across a period because of an increase in the nuclear charge
and a decrease in size.
b. Ionization energy decreases from top to bottom down a group because of an increase in atomic radius
and greater electron shielding.
3. After one ionization, the number of protons is greater than the number of electrons. The attractive force on
the remaining electrons is greater. Additionally, the positive ion is smaller than the original atom and so the
attractive force on the outermost electrons is increased due to the decreased distance.
4. Energy is usually released when an atom gains an electron.
5.
a. Group 17 (halogens)
b. Group 1 (alkali metals)
6.
a. K
b. S
c. Br
d. Cs
7. B
8.
a. P
b. O
c. Li
d. Ne
9. After two ionizations, the Ca2+ ion that results has the electron configuration of a noble gas (argon). Removing
a third electron would require the removal of an electron from the filled n = 3 principal energy level. This is
much more difficult because of decreased distance to the nucleus and less electron shielding.
10.
a. Na
b. Br
c. Ca2+
d. O2
11.
a. F
b. S
c. Be
d. Al
12. C
13. Al
14. P
15. Formation of the Na2+ ion would require the loss of two electrons. Since Na has only one valence electron, it
would require removal of an electron from a filled n = 2 principal energy level. The second ionization energy
is thus so high as to make the process unlikely.
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