Electron Config and Quantum Numbers: Exercises

We’ve already seen how to build electron configurations

Its time to talk about the Quantum numbers

Sulfur, has 16 electrons:

Now lets get the Quantum numbers of some of the electrons of Sulfur.

 Quatum numbers of the LAST electron of Sulfur

First you will have to find out where is located the electron, the last electron is here

This is the n quantum number

This tells us the quantum number, in this case p ----> = 1

To get the last 2 numbers lets use this method:

Draw squares, one for each type of orbital, for p:

Now find the middle square and mark it as 0, squares in the right are positive, squares in the left are negative.

Start filling the squares with arrows representing the electrons, but careful, do it this way:

Now that you’ve filled all with one electron, start over and now the arrow will be downwards.

How many electrons where on this subshell (for Sulfur)? There were 4 so we only fill 4 electrons; the last one you marked is the last electron.

Its m quantum number is -1

Upward arrows have S = ½ and downward arrows have S = - ½

So the last electron of Sulfur has:

n = 3

= 1

m = -1

s = -1/2

Now lets get the Quantum numbers for the Sulfur 9^th electron

That electron is here, so:

 Now the last 2 quantum numbers

Quantum numbers for the Sulfur 9^th electron

n = 2

= 1

m = 0

s = -1/2

Electron Configuration for Excited State

In ground state the number of electrons is equal to the number of protons giving the atom a neutral charge.

In excited charge status the atom has lost/gain electrons, this can be because of a chemical reaction or radiation.

Sodium (Na) has 11 electrons, but what happens with excited Sodium (Na⁺¹)

As you can see the charge of Sodium is +1, that indicates that the atom has lost 1 negative charge being that an electron; so excited sodium has 10 electrons, 1 less than its ground state.

Oxygen (O) in ground state has 8 electrons, but excited Oxygen (O^-2) has a negative charge of -2, meaning that it gained 2 electrons, getting 10 total electrons on excited state.

The process of building the electron configuration now is the same, just make sure you have the correct number of electrons for that atom.

Ground State

O = 1s² 2s² 2p⁴

Excited State

O^-2 = 1s² 2s² 2p⁶

Some Periodic tables come with electron configurations included, but in that tiny square the whole configuration of lets say, Lead that has 82 electrons, wouldn’t fit in, that’s why we use one of our friends, the noble gases.

A peculiar characteristic of these elements is that the last shell of the atom is ALWAYS FULL.

So we use them to avoid writing a long electron configuration:

Lead, has 82 electrons:

Pb = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p²

Pretty long right? Now lets make the configuration of the Noble gas BEFORE Lead.

Xenon: with 54 electrons:

Xe =1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶

The short configuration for Lead would be:

Pb = [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p²

This is what you will find in some Periodic Tables.

Coming up!! Inorganic Chemical Reactions: Oxides