Answers and Explanations

REVIEW QUESTIONS

1 . B

Magnesium   has an  atomic  number  of  12, meaning that    a   neutral atom    has 12  protons and 12

electrons.  However,    the Mg2+    ion has a   positive    charge  because it  has lost    2   electrons.

Therefore,  the Mg2+    ion has 10  electrons.

2 . 35.5

Mass    spectrometry    shows   that    3   out of  every   4   chlorine    atoms   are Cl-35   and 1   is  Cl-37.  Thus,

75% of  all chlorine    atoms   are Cl-35   and 25% are Cl-37.  Using   this    information and the atomic

weights of  the isotopes    (Cl-35  =   35  g/mol,  Cl-37   =   37  g/mol), the atomic  weight  of  chlorine    can

be  determined  as  follows:

3 . D

The maximum number  of  electrons   within  a   principal   energy  level   is  given   by  the equation    2n^2.

Therefore,  a   shell   with    the principal   quantum number  of  4   will    hold    a   maximum of  32

electrons.

4 . B

When    the principal   quantum number  is  equal   to  2,  then    the azimuthal   quantum number  will

have    values  of  l   =   0   and 1.  When    l   =   0,  the subshell    is  an  s   subshell,   and when    l   =   1,  the subshell

is  a   p subshell. Therefore,  the second  principal   energy  level   contains    an  s   subshell    and a   p

subshell.

5 . D

The azimuthal   quantum number  2   corresponds to  the sublevel    or  subshell    d,  and the d