Electron Configuration Example Script
This video demonstrates how to write electron configurations and draw orbital diagrams
for main group elements.
To write an electron configuration you could memorize the order in which orbitals are
filled according to their energy level, but a more convenient method is to use the
periodic table. The periodic table is arranged in blocks, each block represents an
orbital, and each space in the block counts as one electron. The s block is the first two
left-hand columns of the periodic table and includes helium. The p block is the last six
columns on the right hand side stating at boron. The d block is the transition metals in
the middle of the periodic table, and the f block is the lanthanide and actinide series.
To begin start at the top left hand corner of the periodic table and work your way down
by reading across a row from left to right and filling in the proper amount of electrons for
each orbital until you reach your element.
Use the number assigned to each row, 1 thru 7, as the value of the principle quantum
number n, when you arrive at the d and f blocks; subtract one from the n value for the
d orbitals, and two from the n value for the f orbitals.
This periodic table has the electron configuration for each row written along the left
hand side using the method just outlined.
Let’s use it to write the electron configuration of a neutral bromine atom, a bromine atom
has 35 electrons.
Using the blocks in the periodic table we can write the electron configuration of bromine
as: 1s22s22p63s23p64s23d104p5.
If we were writing the electron configuration for the bromine anion, we would begin
writing the same configuration as the neutral bromine atom except the number of
electrons in the p orbitals changes from five to six because the bromine ion has 36
electrons.
To write a shorthand electronic configuration use the chemical symbol of the previous
noble gas in square brackets, for bromine it’s argon, then write out the orbitals that are
occupied by valence electrons.
This makes the shorthand electron configuration for bromine [Ar]4s23d104p5.
The last example is an orbital diagram. We are going to draw the orbital diagram for
oxygen. A neutral oxygen atom has 8 electrons, so the orbitals that will contain
electrons are the 1s, 2s and 2p. The levels need to be arranged in order of increasing
energy, and the lowest energy level orbitals are filled first.
