# The Naked Scientists Forum

### Author Topic: Why does potassium have the electron configuration that it does?  (Read 17996 times)

#### RyanGuyardo

• Jr. Member
• Posts: 28
##### Why does potassium have the electron configuration that it does?
« on: 04/09/2009 01:27:35 »
The number of electrons in each shell in atomic structure is Ne=2n2
So, the 3rd shell can have a maximum number of electrons of 18.
That's why Sodium, Na is 2.8.1 and Magnesium, Mg is 2.8.2
Why isn't Potassium, K 2.8.9 but 2.8.8.1(a total of 4 shells)?
« Last Edit: 04/09/2009 20:11:32 by chris »

#### Chemistry4me

• Neilep Level Member
• Posts: 7709
##### Re: Why does potassium have the electron configuration that it does?
« Reply #1 on: 04/09/2009 04:57:23 »
Actually, that should be the 3rd energy level (n=3) can hold maximum 18 electrons.
Basically what's going on here is that within energy levels you have different 'sublevels'. For example, the first energy level has one sublevel and the second has two and so on, in general, the nth energy level has n sublevels.
Electrons in each sublevel may be found in different regions in space around the nucleus, they are said to occupy different orbitals. Each orbital can be occupied by one or two electrons. At any energy level, the first sublevel consists of 1 orbital called an 's orbital'; the second sublevel consists of three orbitals called 'p orbitals'; the third sublevel consists of 5 orbitals which are called 'd orbitals'; and the fourth sublevel consists of 7 orbitals which are called 'f orbitals'.
The 4s sublevel (which only has one orbital) has a lower energy than the 3d sublevel (consisting of 5 orbitals) so electrons 'fill' this lower energy 4s orbital first. And since the 4s sublevel is part of the 4th energy level (n=4) you write the configuration of K as 2,8,8,1. Note that this type of eletron configuration is the most basic one and only used to explain trends for the lower elements. The 'proper' electron configuration of K is 1s22s22p63s23p64s1. The superscripts show the number of electrons.
Once the 4s orbital has two electrons, the electrons start to fill the 3d sublevel. Zn has configuration of 1s22s22p63s23p63d104s2. The third energy level is completely filled with 18 electrons (add up the bold superscripts). Since the nth energy level can only have n sublevels, the 3rd energy level has 3 sublevels.

#### glovesforfoxes

• Sr. Member
• Posts: 372
• Matthew 6:21
##### Re: Why does potassium have the electron configuration that it does?
« Reply #2 on: 04/09/2009 20:02:22 »
to add to c4m's excellent post, it's called the aufbau principle if you want to look into it more.

#### lightarrow

• Neilep Level Member
• Posts: 4586
• Thanked: 7 times
##### Why does potassium have the electron configuration that it does?
« Reply #3 on: 05/09/2009 09:21:32 »
The number of electrons in each shell in atomic structure is Ne=2n2
So, the 3rd shell can have a maximum number of electrons of 18.
That's why Sodium, Na is 2.8.1 and Magnesium, Mg is 2.8.2
Why isn't Potassium, K 2.8.9 but 2.8.8.1(a total of 4 shells)?
In addition to the good post from Chemistry4me: they are called "shell" for simplicity but there is not an exact correspondence with distance from the nucleus and so with order of filling.
For example, you could say, for the sake of simplicity, that a tree trunk is lower than the foliage, but actually they are someway 'mixed'.
« Last Edit: 05/09/2009 09:24:56 by lightarrow »

#### The Naked Scientists Forum

##### Why does potassium have the electron configuration that it does?
« Reply #3 on: 05/09/2009 09:21:32 »