Editing Periodic table (section)

== Atomic Structure and Periodicity ==

=== Electron Configuration ===
The arrangement of elements in the periodic table directly reflects their electron configurations. Electrons occupy atomic orbitals according to the Aufbau principle, following the sequence:

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p

Each element's position in the table corresponds to its outermost electron configuration, which largely determines its chemical behavior.
{| class="wikitable" style="float:right; margin:0.5em; text-align:center;"
! style="text-align:right;" |ℓ =
! 0
! 1
! 2
! 3
! 4
! 5
! 6
! rowspan=2 | Shell capacity  (2''n''<sup>2</sup>)<ref>{{cite web |date=6 May 2020 |title=Electron Configurations |url=https://www.chem.fsu.edu/chemlab/chm1045/e_config.html |access-date=17 April 2022 |website=www.chem.fsu.edu |publisher=Florida State University |archive-date=6 May 2022 |archive-url=https://web.archive.org/web/20220506074340/https://www.chem.fsu.edu/chemlab/chm1045/e_config.html |url-status=live }}</ref>
|-
! style="text-align:right;" | Orbital
! s
! p
! d
! f
! g
! h
! i
|-
! ''n'' = 1
| bgcolor="{{element color|s-block}}" | 1s
| colspan=6 |
| 2
|-
! ''n'' = 2
| bgcolor="{{element color|s-block}}" | 2s
| bgcolor="{{element color|p-block}}" | 2p
| colspan=5 |
| 8
|-
! ''n'' = 3
| bgcolor="{{element color|s-block}}" | 3s
| bgcolor="{{element color|p-block}}" | 3p
| bgcolor="{{element color|d-block}}" | 3d
| colspan=4 |
| 18
|-
! ''n'' = 4
| bgcolor="{{element color|s-block}}" | 4s
| bgcolor="{{element color|p-block}}" | 4p
| bgcolor="{{element color|d-block}}" | 4d
| bgcolor="{{element color|f-block}}" | 4f
| colspan=3 |
| 32
|-
! ''n'' = 5
| bgcolor="{{element color|s-block}}" | 5s
| bgcolor="{{element color|p-block}}" | 5p
| bgcolor="{{element color|d-block}}" | 5d
| bgcolor="{{element color|f-block}}" | 5f
| bgcolor="{{element color|g-block}}" | 5g
| colspan=2 |
| 50
|-
! ''n'' = 6
| bgcolor="{{element color|s-block}}" | 6s
| bgcolor="{{element color|p-block}}" | 6p
| bgcolor="{{element color|d-block}}" | 6d
| bgcolor="{{element color|f-block}}" | 6f
| bgcolor="{{element color|g-block}}" | 6g
| bgcolor="{{element color|h-block}}" | 6h
|
| 72
|-
! ''n'' = 7
| bgcolor="{{element color|s-block}}" | 7s
| bgcolor="{{element color|p-block}}" | 7p
| bgcolor="{{element color|d-block}}" | 7d
| bgcolor="{{element color|f-block}}" | 7f
| bgcolor="{{element color|g-block}}" | 7g
| bgcolor="{{element color|h-block}}" | 7h
| bgcolor="{{element color|i-block}}" | 7i
| 98
|-
! Subshell capacity (4ℓ+2)
| 2
| 6
| 10
| 14
| 18
| 22
| 26
|
|}
=== Periodic Trends ===
Several key properties show regular patterns across the periodic table:

# '''Atomic Radius'''
#* Generally decreases from left to right across a period
#* Increases down a group
#* Shows pronounced first-row anomalies due to the absence of inner electrons
# '''Ionization Energy'''
#* Generally increases from left to right across a period
#* Decreases down a group
#* Reflects the difficulty of removing electrons
# '''Electron Affinity'''
#* Generally increases from left to right (excluding noble gases)
#* Shows more complex patterns down groups
#* Indicates tendency to accept electrons
# '''Electronegativity'''
#* Increases from left to right
#* Decreases down groups
#* Highest in fluorine, lowest in francium (excluding noble gases)