Editing Term symbol (section)

=== Atomic term symbols of the chemical elements ===
In the periodic table, because atoms of elements in a column usually have the same outer electron structure, and always have the same electron structure in the "s-block" and "p-block" elements (see [[block (periodic table)]]), all elements may share the same ground state term symbol for the column. Thus, hydrogen and the [[alkali metal]]s are all <sup>2</sup>S<sub>{{frac|1|2}}</sub>, the [[alkaline earth metal]]s are  <sup>1</sup>S<sub>0</sub>, the boron column elements are <sup>2</sup>P<sub>{{frac|1|2}}</sub>, the carbon column elements are <sup>3</sup>P<sub>0</sub>, the [[pnictogen]]s are <sup>4</sup>S<sub>{{frac|3|2}}</sub>, the [[chalcogen]]s are <sup>3</sup>P<sub>2</sub>, the [[halogen]]s are <sup>2</sup>P<sub>{{frac|3|2}}</sub>, and the [[inert gas]]es are <sup>1</sup>S<sub>0</sub>, per the rule for full shells and subshells stated above.

Term symbols for the ground states of most chemical elements<ref>{{cite web |url=https://physics.nist.gov/PhysRefData/ASD/ionEnergy.html |title=NIST Atomic Spectra Database Ionization Energies Form |publisher=National Institute of Standards and Technology (NIST) |website=NIST Physical Measurement Laboratory |quote=This form provides access to NIST critically evaluated data on ground states and ionization energies of atoms and atomic ions. |date=October 2018 |access-date=28 January 2019}}</ref> are given in the collapsed table below.<ref>For the sources for these term symbols in the case of the heaviest elements, see [[Template:Infobox element/symbol-to-electron-configuration/term-symbol]].<!-- Do not use "here" as link text. If you don't want to link to template space, perhaps transclude the citations below as well. --></ref> In the d-block and f-block, the term symbols are not always the same for elements in the same column of the periodic table, because open shells of several d or f electrons have several closely spaced terms whose energy ordering is often perturbed by the addition of an extra complete shell to form the next element in the column.

For example, the table shows that the first pair of vertically adjacent atoms with different ground-state term symbols are V and Nb. The <sup>6</sup>D<sub>{{frac|1|2}}</sub> ground state of Nb corresponds to an excited state of V 2112&nbsp;cm<sup>−1</sup> above the <sup>4</sup>F<sub>{{frac|3|2}}</sub> ground state of V, which in turn corresponds to an excited state of Nb 1143&nbsp;cm<sup>−1</sup> above the Nb ground state.<ref name=NIST/> These energy differences are small compared to the 15158&nbsp;cm<sup>−1</sup> difference between the ground and first excited state of Ca,<ref name=NIST/> which is the last element before V with no d electrons.

{| class="mw-collapsible {{#if:{{{state|collapsed}}}|collapsed|mw-collapsed}}" border="0" cellpadding="0" cellspacing="1" style="text-align:center; background:{{Element color|table background}}; border:1px solid {{Element color|table border}}; width:100%; max-width:1300px; margin:0 auto; padding:2px;;"
! colspan=20 style="background:{{Element color|table title}}; padding:2px 4px;" | [[Term symbol]] of the chemical elements
|- style="background:{{Element color|table colheader}}"
! style="width:4.4%; padding:0; margin:0; text-align:right" | <small>[[Periodic table group|Group]]&nbsp;→</small>
! width="5.2%" | [[Alkali metal|1]]
! width="5.2%" | [[Alkaline earth metal|2]]
! width="2%" |
! width="5.2%" | [[Group 3 element|3]] 
! width="5.2%" | [[Group 4 element|4]]
! width="5.2%" | [[Group 5 element|5]]
! width="5.2%" | [[Group 6 element|6]]
! width="5.2%" | [[Group 7 element|7]]
! width="5.2%" | [[Group 8 element|8]]
! width="5.2%" | [[Group 9 element|9]]
! width="5.2%" | [[Group 10 element|10]]
! width="5.2%" | [[Group 11 element|11]]
! width="5.2%" | [[Group 12 element|12]]
! width="5.2%" | [[Boron group|13]]
! width="5.2%" | [[Carbon group|14]]
! width="5.2%" | [[Pnictogen|15]]
! width="5.2%" | [[Chalcogen|16]]
! width="5.2%" | [[Halogen|17]]
! width="5.2%" | [[Noble gas|18]]
|-
! colspan="3" style="text-align:left" | <small>↓&nbsp;[[Periodic table period|Period]]</small>
| colspan="19"|<br />
|-
! [[Period 1 element|1]]
| {{element cell property|H |hydrogen  | term_symbol |s-block| align=diagonal}}
| colspan="17"|<br />
| {{element cell property|He|helium    | term_symbol |s-block| align=diagonal}}
|-
! [[Period 2 element|2]]
| {{element cell property|Li|lithium   | term_symbol |s-block| align=diagonal}}
| {{element cell property|Be|beryllium | term_symbol |s-block| align=diagonal}}
| colspan="11"|<br />
| {{element cell property|B |boron     | term_symbol |p-block| align=diagonal}}
| {{element cell property|C |carbon    | term_symbol |p-block| align=diagonal}}
| {{element cell property|N |nitrogen  | term_symbol |p-block| align=diagonal}}
| {{element cell property|O |oxygen    | term_symbol |p-block| align=diagonal}}
| {{element cell property|F |fluorine  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Ne|neon      | term_symbol |p-block| align=diagonal}}
|-
! [[Period 3 element|3]]
| {{element cell property|Na|sodium    | term_symbol |s-block| align=diagonal}}
| {{element cell property|Mg|magnesium | term_symbol |s-block| align=diagonal}}
| colspan="11"|<br />
| {{element cell property|Al|aluminium | term_symbol |p-block| align=diagonal}}
| {{element cell property|Si|silicon   | term_symbol |p-block| align=diagonal}}
| {{element cell property|P |phosphorus| term_symbol |p-block| align=diagonal}}
| {{element cell property|S |sulfur    | term_symbol |p-block| align=diagonal}}
| {{element cell property|Cl|chlorine  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Ar|argon     | term_symbol |p-block| align=diagonal}}
|-
! [[Period 4 element|4]]
| {{element cell property|K |potassium | term_symbol |s-block| align=diagonal}}
| {{element cell property|Ca|calcium   | term_symbol |s-block| align=diagonal}}
|
| {{element cell property|Sc|scandium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ti|titanium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|V |vanadium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Cr|chromium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Mn|manganese | term_symbol |d-block| align=diagonal}}
| {{element cell property|Fe|iron      | term_symbol |d-block| align=diagonal}}
| {{element cell property|Co|cobalt    | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ni|nickel    | term_symbol |d-block| align=diagonal}}
| {{element cell property|Cu|copper    | term_symbol |d-block| align=diagonal}}
| {{element cell property|Zn|zinc      | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ga|gallium   | term_symbol |p-block| align=diagonal}}
| {{element cell property|Ge|germanium | term_symbol |p-block| align=diagonal}}
| {{element cell property|As|arsenic   | term_symbol |p-block| align=diagonal}}
| {{element cell property|Se|selenium  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Br|bromine   | term_symbol |p-block| align=diagonal}}
| {{element cell property|Kr|krypton   | term_symbol |p-block| align=diagonal}}
|-
! [[Period 5 element|5]]
| {{element cell property|Rb|rubidium  | term_symbol |s-block| align=diagonal}}
| {{element cell property|Sr|strontium | term_symbol |s-block| align=diagonal}}
|
| {{element cell property|Y |yttrium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Zr|zirconium | term_symbol |d-block| align=diagonal}}
| {{element cell property|Nb|niobium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Mo|molybdenum| term_symbol |d-block| align=diagonal}}
| {{element cell property|Tc|technetium| term_symbol |d-block| align=diagonal}}
| {{element cell property|Ru|ruthenium | term_symbol |d-block| align=diagonal}}
| {{element cell property|Rh|rhodium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Pd|palladium | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ag|silver    | term_symbol |d-block| align=diagonal}}
| {{element cell property|Cd|cadmium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|In|indium    | term_symbol |p-block| align=diagonal}}
| {{element cell property|Sn|tin       | term_symbol |p-block| align=diagonal}}
| {{element cell property|Sb|antimony  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Te|tellurium | term_symbol |p-block| align=diagonal}}
| {{element cell property|I |iodine    | term_symbol |p-block| align=diagonal}}
| {{element cell property|Xe|xenon     | term_symbol |p-block| align=diagonal}}
|-
! [[Period 6 element|6]]
| {{element cell property|Cs|caesium   | term_symbol |s-block| align=diagonal}}
| {{element cell property|Ba|barium    | term_symbol |s-block| align=diagonal}}
| {{element cell-asterisk|1}}
| {{element cell property|Lu|lutetium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Hf|hafnium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ta|tantalum  | term_symbol |d-block| align=diagonal}}
| {{element cell property|W |tungsten  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Re|rhenium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Os|osmium    | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ir|iridium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Pt|platinum  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Au|gold      | term_symbol |d-block| align=diagonal}}
| {{element cell property|Hg|mercury   | term_symbol |d-block|Primordial|mercury (element)| align=diagonal}}
| {{element cell property|Tl|thallium  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Pb|lead      | term_symbol |p-block| align=diagonal}}
| {{element cell property|Bi|bismuth   | term_symbol |p-block| align=diagonal}}
| {{element cell property|Po|polonium  | term_symbol |p-block| align=diagonal}}
| {{element cell property|At|astatine  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Rn|radon     | term_symbol |p-block| align=diagonal}}
|-
! [[Period 7 element|7]]
| {{element cell property|Fr|francium     | term_symbol |s-block| align=diagonal}}
| {{element cell property|Ra|radium       | term_symbol |s-block| align=diagonal}}
| {{element cell-asterisk|2vert}}
| {{element cell property|Lr|lawrencium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Rf|rutherfordium| term_symbol |d-block| align=diagonal}}
| {{element cell property|Db|dubnium      | term_symbol |d-block| align=diagonal}}
| {{element cell property|Sg|seaborgium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Bh|bohrium      | term_symbol |d-block| align=diagonal}}
| {{element cell property|Hs|hassium      | term_symbol |d-block| align=diagonal}}
| {{element cell property|Mt|meitnerium   | term_symbol |d-block| align=diagonal}}
| {{element cell property|Ds|darmstadtium | term_symbol |d-block| align=diagonal}}
| {{element cell property|Rg|roentgenium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Cn|copernicium  | term_symbol |d-block| align=diagonal}}
| {{element cell property|Nh|nihonium     | term_symbol |p-block| align=diagonal}}
| {{element cell property|Fl|flerovium    | term_symbol |p-block| align=diagonal}}
| {{element cell property|Mc|moscovium    | term_symbol |p-block| align=diagonal}}
| {{element cell property|Lv|livermorium  | term_symbol |p-block| align=diagonal}}
| {{element cell property|Ts|tennessine   | term_symbol |p-block| align=diagonal}}
| {{element cell property|Og|oganesson    | term_symbol |p-block| align=diagonal}}
|-
| colspan="22"|<br />
|-
| colspan="4" {{element cell-asterisk|1|align=right}}
| {{element cell property|La|lanthanum   | term_symbol |f-block| align=diagonal}}
| {{element cell property|Ce|cerium      | term_symbol |f-block| align=diagonal}}
| {{element cell property|Pr|praseodymium| term_symbol |f-block| align=diagonal}}
| {{element cell property|Nd|neodymium   | term_symbol |f-block| align=diagonal}}
| {{element cell property|Pm|promethium  | term_symbol |f-block| align=diagonal}}
| {{element cell property|Sm|samarium    | term_symbol |f-block| align=diagonal}}
| {{element cell property|Eu|europium    | term_symbol |f-block| align=diagonal}}
| {{element cell property|Gd|gadolinium  | term_symbol |f-block| align=diagonal}}
| {{element cell property|Tb|terbium     | term_symbol |f-block| align=diagonal}}
| {{element cell property|Dy|dysprosium  | term_symbol |f-block| align=diagonal}}
| {{element cell property|Ho|holmium     | term_symbol |f-block| align=diagonal}}
| {{element cell property|Er|erbium      | term_symbol |f-block| align=diagonal}}
| {{element cell property|Tm|thulium     | term_symbol |f-block| align=diagonal}}
| {{element cell property|Yb|ytterbium   | term_symbol |f-block| align=diagonal}}
|-
| colspan="4" {{element cell-asterisk|2vert|align=right}}
| {{element cell property|Ac|actinium    | term_symbol |f-block| align=diagonal}}
| {{element cell property|Th|thorium     | term_symbol |f-block| align=diagonal}}
| {{element cell property|Pa|protactinium| term_symbol |f-block| align=diagonal}}
| {{element cell property|U |uranium     | term_symbol |f-block| align=diagonal}}
| {{element cell property|Np|neptunium   | term_symbol |f-block| align=diagonal}}
| {{element cell property|Pu|plutonium   | term_symbol |f-block| align=diagonal}}
| {{element cell property|Am|americium   | term_symbol |f-block| align=diagonal}}
| {{element cell property|Cm|curium      | term_symbol |f-block| align=diagonal}}
| {{element cell property|Bk|berkelium   | term_symbol |f-block| align=diagonal}}
| {{element cell property|Cf|californium | term_symbol |f-block| align=diagonal}}
| {{element cell property|Es|einsteinium | term_symbol |f-block| align=diagonal}}
| {{element cell property|Fm|fermium     | term_symbol |f-block| align=diagonal}}
| {{element cell property|Md|mendelevium | term_symbol |f-block| align=diagonal}}
| {{element cell property|No|nobelium    | term_symbol |f-block| align=diagonal}}
|-
| <br>
|-
| colspan=20 | 
{{periodic table legend
|theme1=Block|unknown1=no}}
|}