Editing Periodic table

The periodic table is one of the most significant achievements in science and serves as a cornerstone of modern chemistry. It provides an organized arrangement of all known chemical elements, displaying their properties, relationships, and periodic trends in a systematic way. This comprehensive guide explores the structure, history, and significance of this remarkable scientific tool.

== Overview ==
The periodic table arranges chemical elements in rows ("periods") and columns ("groups") according to their atomic numbers and electron configurations. This arrangement reflects the periodic law, which states that the chemical and physical properties of elements follow periodic patterns when arranged by atomic number. The table is divided into four main blocks - s, p, d, and f - each corresponding to the type of atomic orbital being filled with electrons.

=== Basic Structure ===
The modern periodic table contains:

* 7 horizontal periods
* 18 vertical groups
* 118 confirmed elements (as of 2024)
* 4 distinct blocks (s, p, d, f)

Elements in the same group share similar chemical properties due to their similar outer electron configurations. The table can be presented in various formats, with the most common being the 18-column or "medium-long" form, where the f-block elements (lanthanides and actinides) are shown separately below the main table.

== 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)

== Classification of Elements ==

=== Major Categories ===

# '''Metals''' (≈75% of elements)
#* Generally good conductors of heat and electricity
#* Typically malleable and ductile
#* Usually form positive ions
#* Located on the left and center of the table
# '''Nonmetals'''
#* Poor conductors
#* Typically brittle as solids
#* Often form negative ions
#* Located on the right side of the table
# '''Metalloids'''
#* Exhibit properties intermediate between metals and nonmetals
#* Include elements such as silicon, germanium, and arsenic
#* Form a diagonal border between metals and nonmetals

=== Blocks ===

# '''s-block'''
#* Groups 1 and 2
#* Includes alkali metals and alkaline earth metals
#* Characterized by s-orbital filling
# '''p-block'''
#* Groups 13-18
#* Includes many nonmetals and metalloids
#* Shows diverse chemical behaviors
# '''d-block'''
#* Groups 3-12
#* Contains transition metals
#* Exhibits variable oxidation states
# '''f-block'''
#* Lanthanides and actinides
#* Shows similar chemical properties within each series
#* Complex electronic structures

== Historical Development ==

=== Early Attempts ===
The first systematic organization of elements began in the early 19th century:

* 1817: Johann Döbereiner identified chemical triads
* 1863: John Newlands proposed the Law of Octaves
* 1864: Lothar Meyer developed an early version based on atomic volumes

=== Mendeleev's Breakthrough ===
Dmitri Mendeleev published his first periodic table in 1869, making several crucial innovations:

* Arranged elements by atomic weight
* Left gaps for undiscovered elements
* Successfully predicted properties of unknown elements
* Focused on chemical properties rather than physical properties

=== Modern Developments ===
The periodic table continued to evolve through the 20th century:

* 1913: Henry Moseley established atomic number as the fundamental organizing principle
* 1940s: Glenn Seaborg's work on transuranium elements led to the actinide concept
* 1945: Development of the modern form with separate f-block
* 2016: Completion of the seventh period with elements 113, 115, 117, and 118

== Contemporary Challenges and Future Extensions ==

=== Superheavy Elements ===
The synthesis and study of superheavy elements presents several challenges:

* Increasing difficulty of synthesis
* Extremely short half-lives
* Complex relativistic effects
* Uncertain chemical properties

=== Theoretical Limits ===
Several factors may limit the extent of the periodic table:

* Nuclear stability
* Relativistic effects
* Practical synthesizability
* Chemical accessibility

=== Eighth Period ===
Theoretical predictions for the eighth period suggest:

* Different electron configuration patterns
* Possible breakdown of periodic trends
* Complex relativistic effects
* Uncertain chemical behavior

== Alternative Formats ==
The periodic table exists in many alternative formats, each emphasizing different aspects:

* Long form (32-column)
* Left-step (Janet) table
* Spiral arrangements
* Three-dimensional representations

Each format offers different insights into elemental relationships and periodic patterns.

== Significance and Applications ==
The periodic table remains an indispensable tool in:

* Chemical education
* Research and development
* Materials science
* Nuclear physics
* Theoretical chemistry

Its predictive power and organizational principles continue to guide scientific discovery and understanding.

== Structure ==

* <abbr>v</abbr>
* <abbr>t</abbr>
* <abbr>e</abbr>

Periodic table
{| class="wikitable"
!Group
!1
!2
!
!3
!4
!5
!6
!7
!8
!9
!10
!11
!12
!13
!14
!15
!16
!17
!18
|-
|
|Hydrogen &
alkali metals
|Alkaline earth metals
|
|
|
|
|
|
|
|
|
|
|
|Triels
|Tetrels
|Pnictogens
|Chalcogens
|Halogens
|Noble
gases
|-
!Period


1
|Hydrogen1'''H'''1.0080
| colspan="17" |
|Helium2'''He'''4.0026
|-
!2
|Lithium3'''Li'''6.94
|Beryllium4'''Be'''9.0122
| colspan="11" |
|Boron5'''B'''10.81
|Carbon6'''C'''12.011
|Nitrogen7'''N'''14.007
|Oxygen8'''O'''15.999
|Fluorine9'''F'''18.998
|Neon10'''Ne'''20.180
|-
!3
|Sodium11'''Na'''22.990
|Magnesium12'''Mg'''24.305
| colspan="11" |
|Aluminium13'''Al'''26.982
|Silicon14'''Si'''28.085
|Phosphorus15'''P'''30.974
|Sulfur16'''S'''32.06
|Chlorine17'''Cl'''35.45
|Argon18'''Ar'''39.95
|-
!4
|Potassium19'''K'''39.098
|Calcium20'''Ca'''40.078
|
|Scandium21'''Sc'''44.956
|Titanium22'''Ti'''47.867
|Vanadium23'''V'''50.942
|Chromium24'''Cr'''51.996
|Manganese25'''Mn'''54.938
|Iron26'''Fe'''55.845
|Cobalt27'''Co'''58.933
|Nickel28'''Ni'''58.693
|Copper29'''Cu'''63.546
|Zinc30'''Zn'''65.38
|Gallium31'''Ga'''69.723
|Germanium32'''Ge'''72.630
|Arsenic33'''As'''74.922
|Selenium34'''Se'''78.971
|Bromine35'''Br'''79.904
|Krypton36'''Kr'''83.798
|-
!5
|Rubidium37'''Rb'''85.468
|Strontium38'''Sr'''87.62
|
|Yttrium39'''Y'''88.906
|Zirconium40'''Zr'''91.224
|Niobium41'''Nb'''92.906
|Molybdenum42'''Mo'''95.95
|Technetium43'''Tc'''[97]
|Ruthenium44'''Ru'''101.07
|Rhodium45'''Rh'''102.91
|Palladium46'''Pd'''106.42
|Silver47'''Ag'''107.87
|Cadmium48'''Cd'''112.41
|Indium49'''In'''114.82
|Tin50'''Sn'''118.71
|Antimony51'''Sb'''121.76
|Tellurium52'''Te'''127.60
|Iodine53'''I'''126.90
|Xenon54'''Xe'''131.29
|-
!6
|Caesium55'''Cs'''132.91
|Barium56'''Ba'''137.33
|
|Lutetium71'''Lu'''174.97
|Hafnium72'''Hf'''178.49
|Tantalum73'''Ta'''180.95
|Tungsten74'''W'''183.84
|Rhenium75'''Re'''186.21
|Osmium76'''Os'''190.23
|Iridium77'''Ir'''192.22
|Platinum78'''Pt'''195.08
|Gold79'''Au'''196.97
|Mercury80'''Hg'''200.59
|Thallium81'''Tl'''204.38
|Lead82'''Pb'''207.2
|Bismuth83'''Bi'''208.98
|Polonium84'''Po'''[209]
|Astatine85'''At'''[210]
|Radon86'''Rn'''[222]
|-
!7
|Francium87'''Fr'''[223]
|Radium88'''Ra'''[226]
|
|Lawrencium103'''Lr'''[266]
|Rutherfordium104'''Rf'''[267]
|Dubnium105'''Db'''[268]
|Seaborgium106'''Sg'''[269]
|Bohrium107'''Bh'''[270]
|Hassium108'''Hs'''[269]
|Meitnerium109'''Mt'''[278]
|Darmstadtium110'''Ds'''[281]
|Roentgenium111'''Rg'''[282]
|Copernicium112'''Cn'''[285]
|Nihonium113'''Nh'''[286]
|Flerovium114'''Fl'''[289]
|Moscovium115'''Mc'''[290]
|Livermorium116'''Lv'''[293]
|Tennessine117'''Ts'''[294]
|Oganesson118'''Og'''[294]
|-
| colspan="20" |
|-
|
|
|
|
|Lanthanum57'''La'''138.91
|Cerium58'''Ce'''140.12
|Praseodymium59'''Pr'''140.91
|Neodymium60'''Nd'''144.24
|Promethium61'''Pm'''[145]
|Samarium62'''Sm'''150.36
|Europium63'''Eu'''151.96
|Gadolinium64'''Gd'''157.25
|Terbium65'''Tb'''158.93
|Dysprosium66'''Dy'''162.50
|Holmium67'''Ho'''164.93
|Erbium68'''Er'''167.26
|Thulium69'''Tm'''168.93
|Ytterbium70'''Yb'''173.05
|
|
|-
| colspan="3" |
|
|Actinium89'''Ac'''[227]
|Thorium90'''Th'''232.04
|Protactinium91'''Pa'''231.04
|Uranium92'''U'''238.03
|Neptunium93'''Np'''[237]
|Plutonium94'''Pu'''[244]
|Americium95'''Am'''[243]
|Curium96'''Cm'''[247]
|Berkelium97'''Bk'''[247]
|Californium98'''Cf'''[251]
|Einsteinium99'''Es'''[252]
|Fermium100'''Fm'''[257]
|Mendelevium101'''Md'''[258]
|Nobelium102'''No'''[259]
|
|}
Primordial From decay Synthetic '''Border''' shows natural occurrence of the element

'''Standard atomic weight''' ''A''<sub>r, std</sub>(E)

* Ca: 40.078 — Abridged value (uncertainty omitted here)
* Po: [209] — mass number of the most stable isotope

{| class="wikitable"
|s-block
|f-block
|d-block
|p-block
|}

== Conclusion ==
The periodic table stands as one of science's greatest achievements, providing a framework for understanding chemical elements and their relationships. Its development continues as new elements are synthesized and our understanding of atomic structure deepens. Despite challenges in extending it beyond the seventh period, it remains a cornerstone of chemical science and education.