# Problem: Consider the stable elements through lead (Z=82).In how many instances are the atomic weights of the elements out of order relative to the atomic numbers of the elements?

###### FREE Expert Solution

We’re asked to determine how many instances in the periodic table are the atomic weights of the elements out of order relative to the atomic numbers of the elements considering the stable elements through lead (Z=82).

Recall that elements in the periodic table are arranged in order of increasing atomic numbers

The first known periodic table was made by Mendeleev.  He arranged elements in order of increasing mass and observed that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way (arranged in periods/rows).

We will examine using a periodic table, whether elements with atomic numbers 1 to 82 are arranged in order of increasing atomic mass along with an increasing atomic number, Z.

###### Problem Details

Consider the stable elements through lead (Z=82).

In how many instances are the atomic weights of the elements out of order relative to the atomic numbers of the elements?