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[[File:Calcium.jpg|thumb|Calcium metal in air, corroded]]

[[File:Calcium.jpg|thumb|Calcium metal in air, corroded]]

'''Calcium''' is a [[chemical element]]. Its symbol on the [[periodic table]] (a list of all the elements) is '''Ca'''. Its [[atomic number]] is 20. (The atomic number says where Calcium sits in the periodic table.) It has 20 [[proton]]s and 20 [[electron]]s (if is an atom, see [[ion]]). The most common [[isotope]]s are Ca-40 and Ca-44. Its [[mass number]] is about 40.08.

'''Calcium''' is a [[chemical element]]. Its symbol on the [[periodic table]] (a list of all the elements) is '''Ca'''. Its [[atomic number]] is 20. (The atomic number says where Calcium sits in the periodic table.) It has 20 [[proton]]s and 20 [[electron]]s (if is an atom, see [[ion]]). The most common [[isotope]]s are Ca-40 and Ca-44. Its [[mass number]] is about 40.08.

Calcium is very important in the human body, for making [[bone]]s and for other purposes.  

Calcium is very important in the human body, for making [[bone]]s and for other purposes.

== Physical properties ==

=== Physical properties ===

Calcium is a soft white-gray [[metal]]. It is a solid and is opaque. It is an [[alkaline earth metal]].  Its [[melting point]] is hotter than most other reactive metals.  It is a little harder than [[lead]]. It has two [[allotrope]]s.  It does not conduct electricity as well as copper, but is much lighter in weight.

Calcium is a soft white-gray [[metal]]. It is a solid and is opaque. It is an [[alkaline earth metal]].  Its [[melting point]] is hotter than most other reactive metals.  It is a little harder than [[lead]]. It has two [[allotrope]]s.  It does not conduct electricity as well as copper, but is much lighter in weight.

 

== Chemical properties ==

===Chemical properties===

[[File:Calcium air 2.theora.ogv|thumb|Calcium metal burning]]

[[File:Calcium air 2.theora.ogv|thumb|Calcium metal burning]]

It reacts with water to produce [[hydrogen]] and [[calcium hydroxide]]. It reacts with water very fast when it is powdered. When it is in a chunk, it starts reacting slowly because calcium hydroxide makes a coating that does not dissolve on the calcium. If a little [[acid]] is added to calcium hydroxide, it dissolves it, making the calcium react very fast. It burns when powdered to make a reddish flame. This makes [[calcium oxide]]. It also makes [[calcium nitride]] when heated. It can react with [[halogen]]s to make calcium halides like [[calcium chloride]] with [[chlorine]].  

It reacts with water to produce [[hydrogen]] and [[calcium hydroxide]]. It reacts with water very fast when it is powdered. When it is in a chunk, it starts reacting slowly because calcium hydroxide makes a coating that does not dissolve on the calcium. If a little [[acid]] is added to calcium hydroxide, it dissolves it, making the calcium react very fast. It burns when powdered to make a reddish flame. This makes [[calcium oxide]]. It also makes [[calcium nitride]] when heated. It can react with [[halogen]]s to make calcium halides like [[calcium chloride]] with [[chlorine]].

 

== Calcium compounds ==

===Calcium compounds===

Calcium forms chemical compounds in the +2 [[oxidation state]]. Calcium compounds are colorless. Most calcium compounds are not toxic. They are needed in the human body, actually. They are unreactive as far as calcium ions go. Calcium oxide was used to make [[limelight]]s, which have a flame heating calcium oxide and makes it glow very bright.

Calcium forms chemical compounds in the +2 [[oxidation state]]. Calcium compounds are colorless. Most calcium compounds are not toxic. They are needed in the human body, actually. They are unreactive as far as calcium ions go. Calcium oxide was used to make [[limelight]]s, which have a flame heating calcium oxide and makes it glow very bright.

File:Dusičnan vápenatý.JPG|Calcium nitrate

File:Dusičnan vápenatý.JPG|Calcium nitrate

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== Isotopes ==

===Isotopes===

Calcium has 6 naturally occurring isotopes (⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca, ⁴⁶Ca and ⁴⁸Ca), of which ⁴⁸Ca is very slightly radioactive with a [[half-life]] about 6.4×10¹⁹&nbsp;years.<ref name=Arnold2016>{{Cite journal

Calcium has 6 naturally occuring isotopes (⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca, ⁴⁶Ca and ⁴⁸Ca), of which ⁴⁸Ca is very slightly radioactive with a [[half-life]] about 6.4×10¹⁹&nbsp;years.<ref name=Arnold2016>{{Cite journal

  |last1=Arnold |first1=R.

  |last1=Arnold |first1=R.

  |display-authors=etal

  |display-authors=etal

  |pages=112008

  |pages=112008

  |doi= 10.1103/PhysRevD.93.112008

  |doi= 10.1103/PhysRevD.93.112008

|arxiv=1604.01710|bibcode=2016PhRvD..93k2008A}}</ref> Traces of ⁴¹Ca, ⁴⁵Ca and ⁴⁷Ca are made by cosmic rays striking atoms, and are called [[cosmogenic nuclide]]s. ⁴¹Ca is made by the neutron activation of ⁴⁰Ca in the upper layers of the Earth's crust and has a half-life of 102,000 years. Since it decays to potassium-41, it is a critical indicator of [[solar system]] anomalies.

|arxiv=1604.01710|bibcode=2016PhRvD..93k2008A|s2cid=55485404

}}</ref> Traces of ⁴¹Ca, ⁴⁵Ca and ⁴⁷Ca are made by cosmic rays striking atoms, and are called [[cosmogenic nuclide]]s. ⁴¹Ca is made by the neutron activation of ⁴⁰Ca in the upper layers of the Earth's crust and has a half-life of 102,000 years. Since it decays to potassium-41, it is a critical indicator of [[solar system]] anomalies.

Calcium-40 is the most abundant isotope (96% of all natural calcium), since it comes from radiogenic ⁴⁰K, which has a half-life of 1.25 billion years. However, along with calcium-46, it is theoretically unstable but with a half-life so long it has never been observed to decay.

Calcium-40 is the most abundant isotope (96% of all natural calcium), since it comes from radiogenic ⁴⁰K, which has a half-life of 1.25 billion years. However, along with calcium-46, it is theoretically unstable but with a half-life so long it has never been observed to decay.

== In the ground ==

===In the ground===

[[File:Calcite-cu01abg.jpg|thumb|Calcite]]

[[File:Calcite-cu01abg.jpg|thumb|Calcite]]

Calcium is not found as a metal in the ground; it is too reactive.<ref>{{cite web|title=Calcium: the essentials|url=http://www.webelements.com/calcium/|publisher=WebElements|accessdate=7 February 2016}}</ref> [[Calcium carbonate]], also known as [[calcite]], is the most common calcium mineral.

Calcium is not found as a metal in the ground; it is too reactive.<ref>{{cite web|title=Calcium: the essentials|url=http://www.webelements.com/calcium/|publisher=WebElements|accessdate=7 February 2016}}</ref> [[Calcium carbonate]], also known as [[calcite]], is the most common calcium mineral.

Calcium ions are important to cells, but too many calcium ions can be bad. If a cell gets more calcium ion than it needs, it can die. This is why the amount of calcium ion in cells is highly regulated. Conversely, not enough calcium ion is bad. Cells must have the right amount to function properly.

 

Calcium ions are important to cells, but too many calcium ions can be bad. If a cell gets more calcium ion than it needs it can die. This is why the amount of calcium ion in cells is highly regulated. Conversely, not enough calcium ion is bad. Cells must have the right amount to function properly.

Sometimes cells are unhealthy and need to die in for the body to replace them with new, healthy cells. This keeps the whole [[organism]] healthy. Cells know when they should die and can trigger reactions to end their life cycles in many ways. When this happens it is called [[apoptosis]], also known as a 'programmed cell death' (''planned'' cell death.) One way cells accomplish ''apoptosis'' by taking in toxic levels of calcium ions.

Sometimes cells are unhealthy and need to die in for the body to replace them with new, healthy cells. This keeps the whole [[organism]] healthy. Cells know when they should die and can trigger reactions to end their life cycles in many ways. When this happens it is called [[apoptosis]], also known as a 'programmed cell death' (''planned'' cell death.) One way cells accomplish ''apoptosis'' by taking in toxic levels of calcium ions.

Calcium is very important for the human body.

Calcium is very important for the human body.

 

== Calcium storage ==

=== Calcium storage ===

[[Bone]]s contain most of the calcium ion in the human body. If we need more calcium for our [[blood]], [[muscles]], or other [[tissue (biological)|tissue]], it comes from the bones. If we have extra calcium it goes into bones.

[[Bone]]s contain most of the calcium ion in the human body. If we need more calcium for our [[blood]], [[muscles]], or other [[tissue (biological)|tissue]], it comes from the bones. If we have extra calcium it goes into bones.

Calcium as an element is not found in the human body, just calcium ions in the form of [[chemical compound]]s.

Calcium as an element is not found in the human body, just calcium ions in the form of [[chemical compound]]s.

 

== Calcium regulation ==

=== Calcium regulation ===

Organisms need to keep calcium ion levels very well controlled. High calcium levels are bad, and low calcium levels are bad.

Organisms need to keep calcium ion levels very well controlled. High calcium levels are bad, and low calcium levels are bad.

The body controls calcium levels with many [[hormone]]s. Calcitonin, Parathyroid hormone ([[acronym]] PTH), and [[Vitamin D]] are the most important hormones in ''calcium metabolism''. (Vitamin D works as a hormone but it is called a [[vitamin]].)

The body controls calcium levels with many [[hormone]]s. Calcitonin, Parathyroid hormone ([[acronym]] PTH), and [[Vitamin D]] are the most important hormones in ''calcium metabolism''. (Vitamin D works as a hormone but it is called a [[vitamin]].)

 

== Preparation ==

==Preparation==

Calcium metal is made by [[electrolysis]] of melted [[calcium chloride]]. It has to be very hot to melt it. The calcium metal is liquid.

Calcium metal is made by [[electrolysis]] of melted [[calcium chloride]]. It has to be very hot to melt it. The calcium metal is liquid.

 

== As an element ==

Calcium is used in the [[reduction (chemistry)|reduction]] of other metals. It can also be used to make alloys with other metals.

===As an element===

== As chemical compounds ==

Calcium is used in the [[reduction (chemistry)|reduction]] of other metals. It can also be used to make alloys with other metals.  

 

===As chemical compounds===

[[File:Concrete pouring 0020.jpg|thumb|right|Concrete used to make a building]]

[[File:Concrete pouring 0020.jpg|thumb|right|Concrete used to make a building]]

Calcium compounds are also important in [[chemistry]]. It is important for making things. It is a part of [[cement]] which is needed to make [[concrete]] (a hard substance that many buildings are made from.)

Calcium compounds are also important in [[chemistry]]. It is important for making things. It is a part of [[cement]] which is needed to make [[concrete]] (a hard substance that many buildings are made from.)

Calcium is part of [[calcium oxide]]. Calcium oxide is used to make [[paper]], [[pottery]], food, and to purify water (make it good to drink.) Calcium carbonate is used as a calcium supplement. Calcium permanganate can be used as a rocket [[wikt:propellant|propellant]].

Calcium is part of [[calcium oxide]]. Calcium oxide is used to make [[paper]], [[pottery]], food, and to purify water (make it good to drink.) Calcium carbonate is used as a calcium supplement. Calcium permanganate can be used as a rocket [[propellant|propellant]].

 

== Safety ==

== Safety ==

Calcium is toxic as an element. It reacts with water and makes a strong [[base (chemistry)|base]], calcium hydroxide. Calcium compounds are not toxic unless the [[anion]] is toxic. Calcium permanganate is only toxic because of the [[permanganate]], not the calcium.  Like other [[alkaline earth metal]]s calcium burns easily and brightly.

Calcium is toxic as an element. It reacts with water and makes a strong [[base (chemistry)|base]], calcium hydroxide. Calcium compounds are not toxic unless the [[anion]] is toxic. Calcium permanganate is only toxic because of the [[permanganate]], not the calcium.  Like other [[alkaline earth metal]]s calcium burns easily and brightly.

==Related pages==

 

 

 

== Related pages ==

*[[Calcium compounds]]

*[[Calcium compounds]]

 

== Sources ==

==Sources==

{{Reflist}}

{{Reflist}}

== Other websites ==

== Other websites ==

* [http://en.citizendium.org/wiki/Calcium Calcium] -Citizendium  

* [http://en.citizendium.org/wiki/Calcium Calcium] -Citizendium

{{Periodic Table}}

{{Periodic Table}}

{{authority control}}

{{authority control}}

[[Category:Alkaline earth metals]]

[[Category:Alkaline earth metals]]