Video Transcript
The trend in increasing atomic mass
is observed across the periods of the periodic table from left to right. Which transition metal of the
fourth period is an exception to this trend? (A) Nickel, (B) iron, (C) chromium,
(D) manganese, or (E) scandium.
This question is asking us to
analyze the average atomic masses of transition metals in period four, or the fourth
row of the periodic table. These transition metals make up
atomic numbers 21 through 29 on the periodic table, and their masses increase as
their atomic number increases. To find the exception, we must
simply find the element whose mass does not show an increase from the element before
it.
The average atomic mass of scandium
is 45.0 atomic mass units. We can see that the atomic mass
continually increases until we get to element number 28, nickel. Nickel has an atomic mass of 58.7
atomic mass units, while cobalt, element 27, has an atomic mass of 58.9. Therefore, nickel is the exception
to the increasing atomic mass trend for the period four transition metals. The correct answer is (A)
nickel.
