Electron Configuration

General Chemistry Index

Where are we going with this? Getting to the current models of atomic theory didn't happen over night. This page will give the ability to explain how and why models of atomic structure have changed over time. 

Composition of Atoms: Electron Configuration
How do those electrons arrange themselves? 

Understanding how the electrons are configured is sort of a big deal. Based on how the are arranged in an element's atoms determines how they will behave in the presence of other elements. That's to say that electron configuration plays a huge role in how different elements will react.

Aufbau principle states that electrons fill an atom's atomic orbitals from lowest to highest energy levels. Coming from the German word for "building up," it dictates how we map out electron configurations for elements on the periodic table.

Filling Order and Rules

Lowest energy first: Low energy first: Electrons enter the closest available orbital with the least energy before moving to higher shells.


Standard sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, and 6s.


Capacity limits: s holds 2, p holds 6, d holds 10, and f holds 14


Equal energy orbitals: Orbitals with identical energy get one single electron each before any pairing happens (Hund's rule).

Exceptions to the Rule

Transition metals: Half-filled and fully filled subshells (d⁵ or d¹⁰) provide extra stability.


Chromium and copper

So… orbitals.

1. Electrons are located in orbitals outside the nucleus.

2. Each orbital can hold two electrons.

3. Orbitals occur in sets (which have fancy names).

4. Each set of orbitals represent higher and higher energy levels.

Orbitals and Electron Capacity
Energy Level (n)	Type of Orbital	Number of Orbitals Possible	Total Orbitals	Max Number of Electrons
n1	s	1	1	2
n2	s	1	4	8
	p	3
n3	s	1	9	18
	p	3
	d	5
n4	s	1	16	32
	p	3
	d	5
	f	7

5. Elements are arranged in rows on the periodic table depending on how many sets of orbitals they have.

Periodic Table Row and Energy Level Type	Orbital Configuration	Electrons
1 n1	1s	2
2 n1, n2	1s 2s 2p	2, 8
3 n1, 2n2	1s 2s 2p 3s 3p	2, 8, 8
4 n1, 2n2, n3	1s 2s 2p 3s 3p 4s 3d 4p	2, 8, 18, 8
5 n1, 2n2, 2n3	1s 2s 2p 3s 3p 4s 3d 4p 5s, 4d, 5p	2, 8, 18, 18, 8
6 n1, 2n2, 2n3, n4	1s 2s 2p 3s 3p 4s 3d 4p 5s, 4d, 5p, 6s, 4f, 5d, 6p	2, 8, 18, 32, 18, 8
7 n1, 2n2, 2n3, 2n4	1s 2s 2p 3s 3p 4s 3d 4p 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p	2, 8, 18, 32, 32, 18, 8

6. Elements are arranged in columns on the periodic table depending on how the electrons are filling the available orbitals. For instance (and in simple terms), those in column 1 have only 1 electron in the highest energy level set of orbitals. Those in column 2 have only 2 electrons. Those in column 17 are missing only 1. Those in column 18 have no missing electrons. 

For more info:

https://www.chem.fsu.edu/chemlab/chm1045/e_config.html

https://ptable.com/#Electrons