outermost shell.
Now look at the second statement. Is it true or false?
It’s true: Atoms with 8 electrons in their outermost shell
are stable. The first statement is false, and the second is
true.
- B Here you’re given the configuration and asked to identify the
element. The easiest way to solve this problem is to add up the electrons in
the configuration; you’ll find that their sum is 27. Since the question asks
about an atom, and not an ion, this means the answer is Co, which has the
atomic number 27. The correct answer is (B).
- E Here you’re given the element and asked to identify the electron
configuration. Follow the steps we showed you for writing electron
configurations, and you’ll see that E is correct. If you had trouble writing
the electron configuration, you could also have arrived at the answer by
testing each answer choice. See which answer choices have superscripts
that add up to the atomic number of Tc, which is 43. Then eliminate the
other answer choices, and take your best guess.
- C Do it the easy way: Count up the superscripts. They add up to 54.
Look on the periodic table, and you’ll see that element 54 is xenon. Xenon,
as you can see from the table, is a noble gas.
Drill 2
- D As we said earlier, the emission of gamma rays generally
accompanies other forms of radioactive decay. So (D) is right.
- A In order for its atomic number to be reduced by 2, an atom must
lose 2 protons. In order for its mass to be reduced by 4, it must also lose a
total of 4 nucleons (protons or neutrons). The atom loses 2 protons and 2
neutrons. That’s the description of alpha decay, so (A) is correct.
- B Beta decay—which involves the emission of an electron—converts
a neutron into a proton. Positron emission and electron capture (a decay
process that you don’t need to know for the test) convert a proton into a
neutron. Beta decay is the correct answer; that’s choice (B).
