Editing Lead (section)

== Origin and occurrence ==

{| class="wikitable" style="float:left; margin-right:15px; margin-down:0; font-size:10pt; line-height:11pt;"
|+ style="margin-bottom: 5px;" | Solar System abundances{{sfn|Lodders|2003|pp=1222–1223}}
! style="text-align:center;" | Atomic<br />number
! style="width:45%;"| Element
! style="padding-right: 5px; padding-left: 10px;" | Relative<br />amount
|-
| style="text-align:center;" | 42
| style="text-align:center;"| [[Molybdenum]]
| style="padding-right:5px; text-align:right;"|0.798
|-
| style="text-align:center;" | 46
| style="text-align:center;"| [[Palladium]]
| style="padding-right:5px; text-align:right;"|0.440
|-
| style="text-align:center;"| 50
| style="text-align:center; "| [[Tin]]
| style="padding-right:5px; text-align:right;"|1.146<!--
|-
| colspan=3 style="text-align:center;"| ...
|-
| style="text-align:center;" | 76
| style="text-align:center;"| [[Osmium]]
| style="padding-right:5px; text-align:right;"|0.207-->
|-
| style="text-align:center;" | 78
| style="text-align:center;"| [[Platinum]]
| style="padding-right:5px; text-align:right;"|0.417
|-
| style="text-align:center;" | 80
| style="text-align:center;"| [[Mercury (element)|Mercury]]
| style="padding-right:5px; text-align:right;"|0.127
|- style="background:#ff9;"
| style="text-align:center;" | ''82''
| style="text-align:center;"| ''Lead''
| style="padding-right:5px; text-align:right;"|''1''
|-
| style="text-align:center;" | 90
| style="text-align:center;"| [[Thorium]]
| style="padding-right:5px; text-align:right;"| 0.011
|-
| style="text-align:center;" | 92
| style="text-align:center;"| [[Uranium]]
| style="padding-right:5px; text-align:right;"| 0.003
|}

=== In space ===

Lead's per-particle abundance in the [[Solar System]] is 0.121&nbsp;[[Parts-per notation|ppb]] (parts per billion).{{sfn|Lodders|2003|pp=1222–1223}}{{efn|Abundances in the source are listed relative to silicon rather than in per-particle notation. The sum of all elements per 10<sup>6</sup> parts of silicon is 2.6682{{e|10}} parts; lead comprises 3.258 parts.}} This figure is two and a half times higher than that of [[platinum]], eight times more than [[Mercury (element)|mercury]], and seventeen times more than [[gold]].{{sfn|Lodders|2003|pp=1222–1223}} The amount of lead in the [[universe]] is slowly increasing{{sfn|Roederer|Kratz|Frebel|Christlieb|2009|pp=1963–1980}} as most heavier atoms (all of which are unstable) gradually decay to lead.{{sfn|Lochner|Rohrbach|Cochrane|2005|p=12}} The abundance of lead in the Solar System since its formation 4.5&nbsp;billion years ago has increased by about 0.75%.{{sfn|Lodders|2003|p=1224}} The Solar System abundances table shows that lead, despite its relatively high atomic number, is more prevalent than most other elements with atomic numbers greater than 40.{{sfn|Lodders|2003|pp=1222–1223}}

Primordial lead—which comprises the isotopes lead-204, lead-206, lead-207, and lead-208—was mostly created as a result of repetitive neutron capture processes occurring in stars. The two main modes of capture are the [[s-process|s-]] and [[r-process]]es.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=608–615}}

In the s-process (s is for "slow"), captures are separated by years or decades, allowing less stable nuclei to undergo [[beta decay]].{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=551}} A stable thallium-203 nucleus can capture a neutron and become thallium-204; this undergoes beta decay to give stable lead-204; on capturing another neutron, it becomes lead-205, which has a half-life of around 17&nbsp;million years. Further captures result in lead-206, lead-207, and lead-208. On capturing another neutron, lead-208 becomes lead-209, which quickly decays into bismuth-209. On capturing another neutron, bismuth-209 becomes bismuth-210, and this beta decays to polonium-210, which alpha decays to lead-206. The cycle hence ends at lead-206, lead-207, lead-208, and bismuth-209.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=608–609}}

[[File:S-R-processes-atomic-mass-201-to-210.svg|thumb|right|upright=1.15|Chart of the final part of the [[s-process]], from [[mercury (element)|mercury]] to [[polonium]]. Red lines and circles represent [[neutron capture]]s; blue arrows represent [[beta decay]]s; the green arrow represents an [[alpha decay]]; cyan arrows represent [[electron capture]]s.|alt=Uppermost part of the nuclide chart, with only practically stable isotopes and lead-205 shown, and the path of the s-process overlaid on it as well that of the cycle on lead, bismuth, and polonium]]
In the r-process (r is for "rapid"), captures happen faster than nuclei can decay.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=553}} This occurs in environments with a high neutron density, such as a [[supernova]] or the merger of two [[neutron star]]s. The neutron flux involved may be on the order of 10<sup>22</sup> neutrons per square centimeter per second.{{sfn|Frebel|2015|pp=114–115}} The r-process does not form as much lead as the s-process.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=608–610}} It tends to stop once neutron-rich nuclei reach 126 neutrons.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=595}} At this point, the neutrons are arranged in complete shells in the atomic nucleus, and it becomes harder to energetically accommodate more of them.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=596}} When the neutron flux subsides, these nuclei beta decay into stable isotopes of [[osmium]], [[iridium]], [[platinum]].{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=582, 609–615}}

=== On Earth ===
[[File:Lingot de plomb de l'époque romaine. Mines de Cartagène Espagne.jpg|thumb|Lead ingot from Roman times, Cartagena, Spain]]
Lead is classified as a [[Goldschmidt classification#Chalcophile elements|chalcophile]] under the [[Goldschmidt classification]], meaning it is generally found combined with sulfur.{{sfn|Langmuir|Broecker|2012|pp=183–184}} It rarely occurs in its [[native metal|native]], metallic form.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|pp=4–5}} Many lead minerals are relatively light and, over the course of the Earth's history, have remained in the [[Earth's crust|crust]] instead of sinking deeper into the Earth's interior. This accounts for lead's relatively high [[Abundance of elements in Earth's crust|crustal abundance]] of 14&nbsp;ppm; it is the 36th most [[Abundances of the elements (data page)|abundant]] element in the crust.{{sfn|Emsley|2011|pp=286, passim}}{{efn|Elemental abundance figures are estimates and their details may vary from source to source.{{sfn|Cox|1997|p=182}}}}

The main lead-bearing mineral is [[galena]] (PbS), which is mostly found with zinc ores.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=4}} Most other lead minerals are related to galena in some way; [[boulangerite]], Pb<sub>5</sub>Sb<sub>4</sub>S<sub>11</sub>, is a mixed sulfide derived from galena; [[anglesite]], PbSO<sub>4</sub>, is a product of galena oxidation; and [[cerussite]] or white lead ore, PbCO<sub>3</sub>, is a [[Chemical decomposition|decomposition]] product of galena. [[Arsenic]], [[tin]], [[antimony]], [[silver]], [[gold]], [[copper]], [[bismuth]] are common impurities in lead minerals.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=4}}

[[File:Elemental abundances.svg|thumb|left|upright=1.15|Lead is a fairly common element in the [[Earth's crust]] for its high atomic number (82). Most elements of atomic number greater than 40 are less abundant.|alt=A line chart generally declining towards its right]]
World lead resources exceed two billion tons. Significant deposits are located in Australia, China, Ireland, Mexico, Peru, Portugal, Russia, United States. Global reserves—resources that are economically feasible to extract—totaled 88&nbsp;million tons in 2016, of which [[Australia]] had 35&nbsp;million, China 17&nbsp;million, Russia 6.4&nbsp;million.{{sfn|United States Geological Survey|2017|p=97}}

Typical background concentrations of lead do not exceed 0.1&nbsp;μg/m<sup>3</sup> in the atmosphere; 100&nbsp;mg/kg in soil; 4&nbsp;mg/kg in vegetation, 5&nbsp;μg/L in fresh water and seawater.{{sfn|Rieuwerts|2015|p=225}}