8. The Machinery Behind The      Periodic Table   Previous PageNext Page
     Buildup of Atoms and the Periodic Table

The tin configuration then can be written [Kr] 4d 5s 5p. (Note: Electronic configurations customarily are written with orbitals in sequence of increasing n and I values (opposite). Thus 3d would come before 4s, and 4d (and 4f if used) before any n = 5 orbitals. This corresponds with the average distance of electrons in these orbitals from the nucleus, and emphasizes that 3d, 4d, and 4f orbitals are buried in the atom even though they are filled late.)

Example 2:
What are the electronic arrangement and atomic number of bromine, the element one row below chlorine in the periodic table?

The outer electron structure of chlorine is 3s 3p, so we would expect that of bromine to be 4s24p5. Hence we can write


Counting electrons give an atomic number of 35.

Example 3:
Iron (Fe) is the sixth transition metal from the left in row four of the table. What is its electronic structure?

  Page 19 of 32 HomeGlossary