Orbital Diagrams for Period 1 Elements
The Aufbau Principle tells us that atoms of period 1 elements are filling the first energy level (K shell) which is composed of just one s orbital.
The maximum number of electrons that can occupy an orbital is 2.
When 2 electrons occupy the same orbital we apply the Pauli Exclusion Principle so that one electron has a spin quantum number (m_{s}) of +½ (spin up, ↑ or ↿) and the other electron has spin quantum number (m_{s}) of −½ (spin down, ↓ or ⇂).
Hydrogen : atomic number (Z) = 1.
Aufbau Principle: Just 1 electron occupying the s orbital of the 1^{st} energy level (K shell)
electron configuration (shells): 1
electron configuration (subshells): 1s^{1}
orbital diagram (orbital box diagram) : just one electron occupying one box
Helium : atomic number (Z) = 2
Aufbau Principle: 2 electrons occupying the same s orbital of the 1^{st} energy level (K shell)
electron configuration (shells): 2
electron configuration (subshells): 1s^{2}
orbital diagram (orbital box diagram) : apply the Pauli Exclusion Principle so that one electron has the opposite spin to the other (one "up" and one "down")
Orbital Diagrams for Period 2 Elements
The Aufbau Principle tells us that the first energy level (K shell) containing the 1s orbital was completed with the last Period 1 element, helium [He].
Each Period 2 element therefore begins building on this completed 1s orbital (1s^{2}).
The orbital diagram for each Period 2 element will begin with a box occupied by 2 arrows (one up, one down) representing the completed 1s orbital (1s^{2}).
Electrons are then added to the second energy level (L shell) which is made up of one s orbital and 3 p orbitals (p_{x}, p_{y}, p_{z}).
"s block" elements are filling the s orbital, "p block" elements have filled the s orbital and are adding electrons to the p orbitals.
We apply Hund's Rule to maximise the number of unpaired electrons in the p orbitals, that is, electrons will occupy the p orbitals singly until there is 1 electron in each p orbital, after that we must start pairingup the electrons in the p orbitals.
The maximum number of electrons that can occupy an orbital is 2.
When 2 electrons occupy the same orbital we apply the Pauli Exclusion Principle so that one electron has a spin quantum number (m_{s}) of +½ (spin up, ↑ or ↿) and the other electron has spin quantum number (m_{s}) of −½ (spin down, ↓ or ⇂).
Lithium : atomic number (Z) = 3 (s block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), the third electron occupies the s orbital of the second energy level (L shell)
electron configuration (shells): 2,1
electron configuration (subshells): 1s^{2} 2s^{1}
condensed electron configuration: [He] 2s^{1}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 1 arrow
Beryllium : atomic number (Z) = 4 (s block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), the third and fourth electrons occupy the s orbital of the second energy level (L shell)
electron configuration (shells): 2,2
electron configuration (subshells): 1s^{2} 2s^{2}
condensed electron configuration: [He] 2s^{2}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows so we apply the Pauli Exclusion Principle so that one electron is "spin up" and the other is "spin down"
Boron : atomic number (Z) = 5 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 3 electrons occupy the second energy level (L shell), 2 electrons in the 2s orbital as per boron above, but the 5^{th} electron occupies the p subshell of the second energy level (L shell)
electron configuration (shells): 2,3
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{1}
condensed electron configuration: [He] 2s^{2} 2p^{1}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows as per boron above, but now we see that there are 3 orbitals that make up the psubshell (p_{x}, p_{y}, p_{z}), and into one of these we place the 5^{th} arrow
↑↓ 

↑↓ 

↑ 


1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 
Carbon : atomic number (Z) = 6 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 4 electrons occupy the second energy level (L shell), 2 electrons in the 2s orbital as per boron above, but the 5^{th} and 6^{th} electrons occupy the p subshell of the second energy level (L shell)
electron configuration (shells): 2,4
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{2}
condensed electron configuration: [He] 2s^{2} 2p^{2}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows as per boron above, but now we see that there are 3 orbitals that make up the psubshell (p_{x}, p_{y}, p_{z}), into which we need to place 2 arrows.
So, we apply Hund's Rule so that we maximise the number of unpaired electrons in all the 2p orbitals, and, we give those electrons parallel spin (arrows point in the same direction):
↑↓ 

↑↓ 

↑ 
↑ 

1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 
Nitrogen : atomic number (Z) = 7 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 5 electrons occupy the second energy level (L shell), 2 of these electrons are in the 2s orbital as per boron above, but the 5^{th}, 6^{th} and 7^{th} electrons occupy the p subshell of the second energy level (L shell)
electron configuration (shells): 2,5
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{3}
condensed electron configuration: [He] 2s^{2} 2p^{3}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows as per boron above, but now we see that there are 3 orbitals that make up the psubshell (p_{x}, p_{y}, p_{z}), into which we need to place 3 arrows.
So, we apply Hund's Rule so that we maximise the number of unpaired electrons in all the 2p orbitals, and, we give those electrons parallel spin (arrows point in the same direction):
↑↓ 

↑↓ 

↑ 
↑ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 
Oxygen : atomic number (Z) = 8 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 6 electrons occupy the second energy level (L shell), 2 of these electrons are in the 2s orbital as per boron above, but the 5^{th}, 6^{th}, 7^{th} and 8^{th} electrons occupy the p subshell of the second energy level (L shell)
electron configuration (shells): 2,6
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{4}
condensed electron configuration: [He] 2s^{2} 2p^{4}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows as per boron above, but now we see that there are 3 orbitals that make up the psubshell (p_{x}, p_{y}, p_{z}), into which we need to place 4 arrows.
So, we apply Hund's Rule so that we maximise the number of unpaired electrons in all the 2p orbitals, and unpaired electrons will have parallel spin.
This means there will be a pair of electrons in one of the boxes.
Apply the Pauli Exclusion Principle to the paired electrons so that one electron is "spin up" and the other is "spin down"
↑↓ 

↑↓ 

↑↓ 
↑ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 
Fluorine : atomic number (Z) = 9 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 7 electrons occupy the second energy level (L shell), 2 of these electrons are in the 2s orbital as per boron above, but the 5^{th}, 6^{th}, 7^{th}, 8^{th} and 9^{th} electrons occupy the p subshell of the second energy level (L shell)
electron configuration (shells): 2,7
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{5}
condensed electron configuration: [He] 2s^{2} 2p^{5}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows as per boron above, but now we need to place 5 arrows in the 3 orbitals that make up the psubshell (p_{x}, p_{y}, p_{z}).
Apply Hund's Rule to maximise the number of unpaired electrons in all the 2p orbitals which means there will be a pair of electrons in two of the psubshell boxes.
Apply the Pauli Exclusion Principle to the paired electrons in each box so that one electron is "spin up" and the other is "spin down"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 
Neon : atomic number (Z) = 10 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the second energy level (L shell), 2 of these electrons are in the 2s orbital as per boron above, but the 5^{th}, 6^{th}, 7^{th}, 8^{th}, 9^{th} and 10^{th} electrons occupy the p subshell of the second energy level (L shell)
electron configuration (shells): 2,8
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6}
condensed electron configuration: [He] 2s^{2} 2p^{6}
orbital diagram (orbital box diagram) : 1s box has 2 arrows (as per helium above), 2s box has 2 arrows as per boron above, but now we need to place 6 arrows in the 3 orbitals that make up the psubshell (p_{x}, p_{y}, p_{z}).
Each p orbital (p_{x}, p_{y}, and p_{z}) will be be occupied by a pair of electrons.
Apply the Pauli Exclusion Principle to the paired electrons in each box so that one electron is "spin up" and the other is "spin down"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 
Orbital Diagrams for Period 3 Elements
The electronic configuration of atoms of all Period 3 elements begins with a completed 1^{st} and 2^{nd} energy level (filled K and L shells), that is, with the electron configuration of the last element of Period 2, the Noble gas neon, [Ne].
The valence electrons (outermost shell electrons, or highest energy level electrons) begin occupying the 3^{rd} energy level (M shell).
The third energy level (M shell) of Period 3 elements is made up of one s orbital and 3 p orbitals (p_{x}, p_{y}, p_{z}).
"s block" elements are filling the s orbital, p block elements have filled the s orbital and are adding electrons to the p orbitals.
We apply Hund's Rule to maximise the number of unpaired electrons in the p orbitals, that is, electrons will occupy the p orbitals singly until there is 1 electron in each p orbital, after that we must start pairingup the electrons in the p orbitals.
The maximum number of electrons that can occupy an orbital is 2.
When 2 electrons occupy the same orbital we apply the Pauli Exclusion Principle so that one electron has a spin quantum number (m_{s}) of +½ (spin up, ↑ or ↿) and the other electron has spin quantum number (m_{s}) of −½ (spin down, ↓ or ⇂).
Sodium : atomic number (Z) = 11 (s block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 1 electron occupies the third energy level (M shell) in an s orbital.
electron configuration (shells): 2,8,1
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{1}
condensed electron configuration: [Ne] 3s^{1}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} boxes, with 1 electron placed in the 3s box
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 
Magnesium : atomic number (Z) = 12 (s block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 2 electrons occupy the third energy level (M shell) in an s orbital.
electron configuration (shells): 2,8,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2}
condensed electron configuration: [Ne] 3s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} boxes, with 2 electrons placed in the 3s box
Apply the Pauli Exclusion Principle so that for paired electrons, one electron has "up spin" and the other has "down spin"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 
Aluminium : atomic number (Z) = 13 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 3 electrons occupy the third energy level (M shell) 2 of these electrons in an s orbital and the 3^{rd} electron in one of the 3 available porbitals (p_{x}, p_{y}, p_{z}).
electron configuration (shells): 2,8,3
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{1}
condensed electron configuration: [Ne] 3s^{2} 3p^{1}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} and 3s boxes, with 1 electron in a 3p box.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑ 


1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 
Silicon : atomic number (Z) = 14 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 4 electrons occupy the third energy level (M shell) 2 of these electrons in an s orbital while the 3^{rd} and 4^{th} electrons occupy the available psubshell.
electron configuration (shells): 2,8,4
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{2}
condensed electron configuration: [Ne] 3s^{2} 3p^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} and 3s boxes, with 2 electrons occupying 3p boxes.
Apply Hund's Rule: maximise the number of unpaired electrons in all the 3p orbitals, that is, there will be 2 unpaired electrons and these will have parallel spin (arrows facing the same direction)
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑ 
↑ 

1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 
Phosphorus : atomic number (Z) = 15 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 5 electrons occupy the third energy level (M shell) 2 of these electrons in an s orbital while the 3^{rd}, 4^{th} and 5^{th} electrons occupy the available psubshell.
electron configuration (shells): 2,8,5
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{3}
condensed electron configuration: [Ne] 3s^{2} 3p^{3}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} and 3s boxes, with 3 electrons occupying 3p boxes.
Apply Hund's Rule: maximise the number of unpaired electrons in all the 3p orbitals, that is, there will be 3 unpaired electrons and they will have parallel spin (arrows pointing in the same direction)
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑ 
↑ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 
Sulfur : atomic number (Z) = 16 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 6 electrons occupy the third energy level (M shell) 2 of these electrons in an s orbital while the 3^{rd}, 4^{th}, 5^{th} and 6^{th} electrons occupy the available psubshell.
electron configuration (shells): 2,8,6
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{4}
condensed electron configuration: [Ne] 3s^{2} 3p^{4}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} and 3s boxes, with 4 electrons occupying 3p boxes.
Apply Hund's Rule: maximise the number of unpaired electrons in all the 3p orbitals, that is, there will be 2 unpaired electrons with parallel spin, and, 1 pair of electrons.
Apply the Pauli Exclusion Principle to the pairs of electrons: 1 electron is "spin up" and the other is "spin down"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 
Chlorine : atomic number (Z) = 17 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 7 electrons occupy the third energy level (M shell) 2 of these electrons in an s orbital while the 3^{rd}, 4^{th}, 5^{th}, 6^{th} and 7^{th} electrons occupy the available psubshell.
electron configuration (shells): 2,8,7
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{5}
condensed electron configuration: [Ne] 3s^{2} 3p^{5}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} and 3s boxes, with 5 electrons occupying all three of the 3p boxes.
Apply Hund's Rule: maximise the number of unpaired electrons in all the 3p orbitals, that is, there will be 1 unpaired electron and 2 pairs of electrons.
Apply the Pauli Exclusion Principle to the pairs of electrons: 1 electron is "spin up" and the other is "spin down"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 
Argon : atomic number (Z) = 18 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the third energy level (M shell) 2 of these electrons in an s orbital while the 3^{rd}, 4^{th}, 5^{th}, 6^{th}, 7^{th} and 8^{th} electrons occupy the available psubshell.
electron configuration (shells): 2,8,8
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6}
condensed electron configuration: [Ne] 3s^{2} 3p^{6}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y} and 2p_{z} and 3s boxes, with 6 electrons occupying 3p boxes, that is, each 3p orbital will contain a pair of electrons.
Apply the Pauli Exclusion Principle to the pairs of electrons: 1 electron is "spin up" and the other is "spin down"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 
Orbital Diagrams for Period 4 Elements
The atoms of Period 4 elements have completed the first energy level (K shell) and the second energy level (L shell).
The 3s and 3p orbitals are also full, so the inner electron shells have the electron configuration of the last period 3 element, the Noble gas Argon [Ar].
The atoms of Period 4 "s block" elements are adding electrons to the ssubshell of the fourth energy level (N shell).
The five d orbitals of the third energy level become available to the "d block" elements (transition metals) in period 4.
These d orbitals are designated 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}
The "p block" elements of Period 4 are filling the psubshell made up of three orbitals (4p_{x}, 4p_{y} and 4p_{z}) of the fourth energy level (N shell).
We apply Hund's Rule to maximise the number of unpaired electrons and the Pauli Exclusion Principle to allocate one electron of a pair electrons in an orbital a spin quantum number (m_{s}) of +½ (spin up, ↑ or ↿) and the other electron of the pair is given a spin quantum number (m_{s}) of −½ (spin down, ↓ or ⇂).
With regards to chromium (Z = 24) we note that the atom gains stability by halffilling both the 4s orbital and all of the 3d orbitals.
In the case of copper (Z = 29) we note that the atom gains stability by having pairs of electrons in all its 3d orbitals but one unpaired electron in the 4s orbital.
Potassium : atomic number (Z) = 19 (s block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the third energy level (M shell) 2 of these electrons occupy the 3s orbital and 6 electrons occupy the available psubshell.
One unpaired electron occupies the s orbital of the fourth energy level (N shell).
electron configuration (shells): 2,8,8,1
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{1}
condensed electron configuration: [Ar] 4s^{1}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and 1 electron occupies the 4s orbital.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

4s 
Calcium : atomic number (Z) = 20 (s block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the third energy level (M shell) 2 of these electrons occupy the 3s orbital and 6 electrons occupy the available psubshell.
One pair of electrons occupy the s orbital of the fourth energy level (N shell).
electron configuration (shells): 2,8,8,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2}
condensed electron configuration: [Ar] 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and 2 electrons occupy the 4s orbital, so we apply the Pauli Exclusion Principle by making one of the electrons "spin up" and the other "spin down"
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

4s 
Scandium : atomic number (Z) = 21 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell), and, one pair of electrons occupy the s orbital of the fourth energy level (N shell)
Scandium is the first of the "d block" elements, so we now need to include a set of five d orbitals in our orbital diagram, with one electron occupying one of these boxes.
electron configuration (shells): 2,8,9,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{1} 4s^{2}
condensed electron configuration: [Ar] 3d^{1} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and 4s orbitals, with one electron occupying a 3d orbital
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 





↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Titanium : atomic number (Z) = 22 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and, one pair of electrons occupy the s orbital of the fourth energy level (N shell)
The electronic configuration of titanium also includes 2 electrons in 3d orbitals
electron configuration (shells): 2,8,10,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{2} 4s^{2}
condensed electron configuration: [Ar] 3d^{2} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and 4s orbitals, with 2 electrons occupying 2 of the 3d orbitals, so we apply Hund's Rule to maximise the number of unpaired electrons and give them parallel spin.
This means that 2 of the 3d orbitals will be occupied by 1 electron and these two arrows will point in the same direction.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 
↑ 




↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Vanadium : atomic number (Z) = 23 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell), and, one pair of electrons occupy the s orbital of the fourth energy level (N shell)
The electronic configuration of vanadium also includes 3 electrons in 3d orbitals
electron configuration (shells): 2,8,11,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{3} 4s^{2}
condensed electron configuration: [Ar] 3d^{3} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and 4s orbitals, with 3 electrons occupying 3 of the 3d orbitals, so we apply Hund's Rule to maximise the number of unpaired electrons and give them parallel spin.
This means that 3 of the 3d orbitals will be occupied by 1 electron and all these arrows will point in the same direction
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 
↑ 
↑ 



↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Chromium : atomic number (Z) = 24 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell).
Note that we need to place 6 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), so the atom will gain greater stability by having all these orbitals halffilled, meaning that each of these orbitals will be occupied by just 1 electron.
electron configuration (shells): 2,8,13,1
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{5} 4s^{1}
condensed electron configuration: [Ar] 3d^{5} 4s^{1}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, but in accordance with Hund's Rule only 1 electron occupies the 4s orbital, and all the 3d orbitals and all these electrons have parallel spin (arrows all point in the same direction)
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 
↑ 
↑ 
↑ 
↑ 

↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Manganese : atomic number (Z) = 25 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy s and p orbitals of the third energy level (M shell).
Note that we need to place 7 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), the atom will gain greater stability by pairing up electrons in the single 4s orbital rather than in one of the 5 available 3d orbitals.
We apply the Pauli Exclusion Principle to this pair of electrons, giving one of the electrons "spin up" and the other "spin down".
electron configuration (shells): 2,8,13,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{5} 4s^{2}
condensed electron configuration: [Ar] 3d^{5} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z} and 4s orbital, and only 1 electron occupies each of the 3d orbitals and these electrons have parallel spin (arrows pointing in the same direction) in accordance with Hund's Rule.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑ 
↑ 
↑ 
↑ 
↑ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Iron : atomic number (Z) = 26 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell).
Note that we need to place 8 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), the atom will gain greater stability by pairing up electrons in the single 4s orbital and in one of the 5 available 3d orbitals.
We apply the Pauli Exclusion Principle to these pairs of electrons, giving one of the electrons "spin up" and the other "spin down".
electron configuration (shells): 2,8,14,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6} 4s^{2}
condensed electron configuration: [Ar] 3d^{6} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, 4s orbital and one of the 3d orbitals, with only 1 electron occupying each of the other 3d orbitals and these electrons have parallel spin (arrows pointing in the same direction) in accordance with Hund's Rule.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑ 
↑ 
↑ 
↑ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Cobalt : atomic number (Z) = 27 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell).
Note that we need to place 9 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), the atom will gain greater stability by pairing up electrons in the single 4s orbital and in two of the 5 available 3d orbitals.
We apply the Pauli Exclusion Principle to these pairs of electrons, giving one of the electrons "spin up" and the other "spin down".
electron configuration (shells): 2,8,15,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{7} 4s^{2}
condensed electron configuration: [Ar] 3d^{7} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, 4s orbital and two of the 3d orbitals, with only 1 electron occupying each of the other 3d orbitals and these electrons have parallel spin (arrows pointing in the same direction) in accordance with Hund's Rule.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑ 
↑ 
↑ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Nickel : atomic number (Z) = 28 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell).
Note that we need to place 10 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), the atom will gain greater stability by pairing up electrons in the single 4s orbital and in three of the 5 available 3d orbitals.
We apply the Pauli Exclusion Principle to these pairs of electrons, giving one of the electrons "spin up" and the other "spin down".
electron configuration (shells): 2,8,16,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{8} 4s^{2}
condensed electron configuration: [Ar] 3d^{8} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, 4s orbital and three of the 3d orbitals, with only 1 electron occupying each of the other 3d orbitals and these electrons have parallel spin (arrows pointing in the same direction) in accordance with Hund's Rule.
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑ 
↑ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Copper : atomic number (Z) = 29 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell).
Note that we need to place 11 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), the atom will gain greater stability in accordance with Hund's Rule by pairing up electrons in the five 3d orbitals and leaving just 1 electron in the 4s orbital
We apply the Pauli Exclusion Principle to these pairs of electrons, giving one of the electrons "spin up" and the other "spin down".
electron configuration (shells): 2,8,18,1
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{1}
condensed electron configuration: [Ar] 3d^{10} 4s^{1}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, with only 1 electron occupying the 4s orbital
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Zinc : atomic number (Z) = 30 (d block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), and 8 electrons occupy the s and p orbitals of the third energy level (M shell).
Note that we will place 12 electrons into 6 orbitals of very similar energy (4s, 3d_{xy}, 3d_{xz}, 3d_{yz}, 3d_{x2−y2} and 3d_{z2}), so that there will be a pair of electrons in each of these orbitals.
We apply the Pauli Exclusion Principle to these pairs of electrons, giving one of the electrons "spin up" and the other "spin down".
electron configuration (shells): 2,8,18,2
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2}
condensed electron configuration: [Ar] 3d^{10} 4s^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, and the 4s orbital
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 
Gallium : atomic number (Z) = 31 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), 18 electrons occupy the completed third energy level (M shell), and, 2 electrons occupy the s orbital of the fourth energy level (N shell).
Now we add an electron to one of the p orbitals of the fourth energy level (remember there are 3 p orbitals making up the psubshell)
electron configuration (shells): 2,8,18,3
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{1}
condensed electron configuration: [Ar] 3d^{10} 4s^{2} 4p^{1}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, and the 4s orbital. One electron occupies a 4p orbital
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑ 


1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 

4p_{x} 
4p_{y} 
4p_{z} 
Germanium : atomic number (Z) = 32 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), 18 electrons occupy the completed third energy level (M shell), and, 2 electrons occupy the s orbital of the fourth energy level (N shell).
Now we add two electrons to the p orbitals of the fourth energy level (remember there are 3 p orbitals making up the psubshell)
electron configuration (shells): 2,8,18,4
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{2}
condensed electron configuration: [Ar] 3d^{10} 4s^{2} 4p^{2}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, and the 4s orbital.
Two electrons occupy 4p orbitals singly
We apply Hund's Rule to maximise the number of unpaired electrons, so the 2 electrons will occupy different 4p orbitals and will have parallel spin (arrows pointing in the same direction)
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑ 
↑ 

1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 

4p_{x} 
4p_{y} 
4p_{z} 
Arsenic : atomic number (Z) = 33 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), 18 electrons occupy the completed third energy level (M shell), and, 2 electrons occupy the s orbital of the fourth energy level (N shell).
Now we add three electrons to the p orbitals of the fourth energy level (remember there are 3 p orbitals making up the psubshell)
electron configuration (shells): 2,8,18,5
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{3}
condensed electron configuration: [Ar] 3d^{10} 4s^{2} 4p^{3}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, and the 4s orbital. Three electrons occupy 4p orbitals singly
We apply Hund's Rule to maximise the number of unpaired electrons, so the 3 electrons will occupy different 4p orbitals and they will have parallel spin (arrows pointing in the same direction)
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑ 
↑ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 

4p_{x} 
4p_{y} 
4p_{z} 
Selenium : atomic number (Z) = 34 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), 18 electrons occupy the completed third energy level (M shell), and, 2 electrons occupy the s orbital of the fourth energy level (N shell).
Now we add four electrons to the p orbitals of the fourth energy level (remember there are 3 p orbitals making up the psubshell)
electron configuration (shells): 2,8,18,6
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{4}
condensed electron configuration: [Ar] 3d^{10} 4s^{2} 4p^{4}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, and the 4s orbital. Four electrons occupy the three 4p orbitals
We apply Hund's Rule to maximise the number of unpaired electrons and give these parallel spin (arrows pointing in the same direction), this means that one of the 4p orbitals must be occupied by a pair of electrons.
Apply the Pauli Exclusion Principle so that one electron of the pair is defined as "spin up" and the other as "spin down".
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 

4p_{x} 
4p_{y} 
4p_{z} 
Bromine : atomic number (Z) = 35 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), 18 electrons occupy the completed third energy level (M shell), and, 2 electrons occupy the s orbital of the fourth energy level (N shell).
Now we add five electrons to the p orbitals of the fourth energy level (remember there are 3 p orbitals making up the psubshell)
electron configuration (shells): 2,8,18,7
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{5}
condensed electron configuration: [Ar] 3d^{10} 4s^{2} 4p^{5}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, and the 4s orbital. Five electrons occupy the three 4p orbitals
Apply the Pauli Exclusion Principle so that one electron of the pair is defined as "spin up" and the other as "spin down".
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 

4p_{x} 
4p_{y} 
4p_{z} 
Krypton : atomic number (Z) = 36 (p block element)
Aufbau Principle: 2 electrons occupy the completed first energy level (K shell), 8 electrons occupy the completed second energy level (L shell), 18 electrons occupy the completed third energy level (M shell), and, 2 electrons occupy the s orbital of the fourth energy level (N shell).
Now we add six electrons to the p orbitals of the fourth energy level (remember there are 3 p orbitals making up the psubshell)
Each of the three 4p orbitals must be occupied by a pair of electrons.
electron configuration (shells): 2,8,18,8
electron configuration (subshells): 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6}
condensed electron configuration: [Ar] 3d^{10} 4s^{2} 4p^{6}
orbital diagram (orbital box diagram) : Pairs of electrons occupy the 1s, 2s, 2p_{x}, 2p_{y}, 2p_{z}, 3s, 3p_{x}, 3p_{y}, 3p_{z}, and each of the five 3d orbitals, the 4s orbital, and the three 4p orbitals
Apply the Pauli Exclusion Principle so that one electron of the pair is defined as "spin up" and the other as "spin down".
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 

↑↓ 
↑↓ 
↑↓ 
↑↓ 
↑↓ 

↑↓ 

↑↓ 
↑↓ 
↑↓ 
1s 

2s 

2p_{x} 
2p_{y} 
2p_{z} 

3s 

3p_{x} 
3p_{y} 
3p_{z} 

3d_{xy} 
3d_{xz} 
3d_{yz} 
3d_{x2−y2} 
3d_{z2} 

4s 

4p_{x} 
4p_{y} 
4p_{z} 