Calcium

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 protons and 20 electrons (if is an atom, see ion). The most common isotopes are Ca-40 and Ca-44. Its mass number is about 40.08. Calcium is very important in the human body, for making bones and for other purposes.

Calcium, ₀₀Ca

Calcium
Appearance	dull gray, silver; with a pale yellow tint
Standard atomic weight Ar°(Ca)
	40.078(4)
Calcium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Mg ↑ Ca ↓ Sr potassium ← calcium → scandium
Group	group 2 (alkaline earth metals)
Period	period 4
Block	s-block
Electron configuration	[Ar] 4s2
Electrons per shell	2, 8, 8, 2
Physical properties
Phase at STP	solid
Melting point	1115 K ​(842 °C, ​1548 °F)
Boiling point	1757 K ​(1484 °C, ​2703 °F)
Density (near r.t.)	1.55 g/cm3
when liquid (at m.p.)	1.378 g/cm3
Heat of fusion	8.54 kJ/mol
Heat of vaporization	154.7 kJ/mol
Molar heat capacity	25.929 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 864 956 1071 1227 1443 1755
Atomic properties
Oxidation states	+1, +2 (a strongly basic oxide)
Electronegativity	Pauling scale: 1.00
Ionization energies	1st: 589.8 kJ/mol 2nd: 1145.4 kJ/mol 3rd: 4912.4 kJ/mol (more)
Atomic radius	empirical: 197 pm
Covalent radius	176±10 pm
Van der Waals radius	231 pm
Spectral lines of calcium
Other properties
Natural occurrence	primordial
Crystal structure	​face-centered cubic (fcc)
Speed of sound thin rod	3810 m/s (at 20 °C)
Thermal expansion	22.3 µm/(m⋅K) (at 25 °C)
Thermal conductivity	201 W/(m⋅K)
Electrical resistivity	33.6 nΩ⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	+40.0·10−6 cm3/mol
Young's modulus	20 GPa
Shear modulus	7.4 GPa
Bulk modulus	17 GPa
Poisson ratio	0.31
Mohs hardness	1.75
Brinell hardness	170–416 MPa
CAS Number	7440-70-2
History
Discovery and first isolation	Humphry Davy (1808)
Isotopes of calcium
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 40Ca 96.9% stable 41Ca trace 9.94×104 y ε 41K 42Ca 0.647% stable 43Ca 0.135% stable 44Ca 2.09% stable 45Ca synth 163 d β− 45Sc 46Ca 0.004% stable 47Ca synth 4.5 d β− 47Sc 48Ca 0.187% 6.4×1019 y β−β− 48Ti

Very pure calcium metal, not corroded

Calcium metal in air, corroded

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 allotropes. It does not conduct electricity as well as copper, but is much lighter in weight.

Chemical properties

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 halogens to make calcium halides like calcium chloride with chlorine.

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 limelights, which have a flame heating calcium oxide and makes it glow very bright.

• Calcium bromate
• Calcium carbonate
• Calcium chloride
• Calcium hydroxide
• Calcium nitrate
• Calcium nitride
• Calcium oxide
• Calcium permanganate
• Calcium phosphate
• Dicalcium phosphate
• Monocalcium phosphate

• 
  Calcium hydroxide
• 
  Calcium chloride
• 
  Calcium sulfate hydrated (with water)
• 
  Calcium nitrate

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 years. Traces of ⁴¹Ca, ⁴⁵Ca and ⁴⁷Ca are made by cosmic rays striking atoms, and are called cosmogenic nuclides. 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.

Occurrence

In the ground

Calcite

Calcium is not found as a metal in the ground; it is too reactive. Calcium carbonate, also known as calcite, is the most common calcium mineral.

Calcium in cells

It is important to know how cells work. Many cells have calcium channels on their surface. These are openings where calcium ions can enter the cell. The cell is told to act and it opens the channels. Once in the cell calcium ions activates many proteins to do specific things. For example, when it goes into muscle cells, it makes them contract (shorten so the muscle pulls.) When it goes into nerve cells, it triggers electrical impulses that send a message. When it goes into white blood cells, it makes them fight germs.

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.

Calcium is very important for the human body.

Calcium storage

Bones contain most of the calcium ion in the human body. If we need more calcium for our blood, muscles, or other 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 compounds.

Calcium regulation

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

The body controls this by changing

• how much calcium we get from the food we eat
• how much calcium we lose in urine
• how much calcium is put in bones

The control of calcium in the body is called calcium metabolism. Too little calcium can cause osteoporosis.

The body controls calcium levels with many hormones. 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

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

Uses

As an element

Calcium is used in the reduction of other metals. It can also be used to make alloys with other metals.

As chemical compounds

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 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.

Safety

Calcium is toxic as an element. It reacts with water and makes a strong 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 metals calcium burns easily and brightly.

Related pages

• Calcium compounds

Other websites

• Calcium -Citizendium