Caesium facts for kids

Caesium (say it: SEE-zee-əm) is a special chemical element you can find on the periodic table. Its number is 55, and its symbol is Cs.

Quick facts for kids
Caesium, ₅₅Cs

Caesium
Pronunciation	/ˈsiːziəm/ ​(SEE-zee-əm)
Appearance	silvery gold
Standard atomic weight Ar, std(Cs)	132.90545196(6)
Caesium 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 Rb ↑ Cs ↓ Fr xenon ← caesium → barium
Atomic number (Z)	55
Group	group 1: hydrogen and alkali metals
Period	period 6
Block	s
Electron configuration	[Xe] 6s1
Electrons per shell	2, 8, 18, 18, 8, 1
Physical properties
Phase at STP	solid
Melting point	301.7 K ​(28.5 °C, ​83.3 °F)
Boiling point	944 K ​(671 °C, ​1240 °F)
Density (near r.t.)	1.93 g/cm3
when liquid (at m.p.)	1.843 g/cm3
Critical point	1938 K, 9.4 MPa
Heat of fusion	2.09 kJ/mol
Heat of vaporization	63.9 kJ/mol
Molar heat capacity	32.210 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 418 469 534 623 750 940
Atomic properties
Oxidation states	−1, +1 (a strongly basic oxide)
Electronegativity	Pauling scale: 0.79
Atomic radius	empirical: 265 pm
Covalent radius	244±11 pm
Van der Waals radius	343 pm
Spectral lines of caesium
Other properties
Natural occurrence	primordial
Crystal structure	​body-centered cubic (bcc)
Thermal expansion	97 µm/(m⋅K) (at 25 °C)
Thermal conductivity	35.9 W/(m⋅K)
Electrical resistivity	205 n Ω⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Young's modulus	1.7 GPa
Bulk modulus	1.6 GPa
Mohs hardness	0.2
Brinell hardness	0.14 MPa
CAS Number	7440-46-2
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct

Caesium is an alkali metal. It has a very low melting point, which means it turns into a liquid easily. It melts at just 28.5 °C (83.3 °F). This is only a little warmer than room temperature!

Caesium is extremely reactive. Because it reacts so easily with other things, it can be dangerous. It can even catch fire by itself in the air. If it touches water, it explodes! This reaction is much stronger than with other alkali metals. To keep it safe, caesium is stored in mineral oil.

Caesium is a rare element. There isn't much of it on Earth, so it costs a lot. Your body does not need caesium. In large amounts, it can be a little harmful. This is because it is similar to potassium, which your body does need.

History of Caesium

Caesium was first found in 1861. Two scientists, Gustav Kirchhoff and Robert Bunsen, discovered it. They were looking at mineral water from a place called Bad Dürkheim.

After they took out other elements like calcium and lithium, they saw two bright blue lines. These lines appeared when they used a special tool called a spectroscope. The blue lines told them there was a new, unknown substance in the water. They named this new element caesium. The name comes from the Latin word for "sky blue."

Caesium's Forms and Uses

Caesium has many different forms called isotopes. Scientists know of at least 39 isotopes of caesium. But only one of them, called ¹³³Cs, is stable. This means it doesn't change over time.

¹³³Cs is the natural form of caesium. It is not radioactive. This stable isotope is very important for atomic clocks. These clocks use the exact vibrations of ¹³³Cs atoms to measure time. This is how we define the length of one second!

Another isotope is ¹³⁷Cs. This one is not found naturally. It is made after a process called nuclear fission. ¹³⁷Cs is very radioactive. It is used in industries as a source of gamma rays.

Caesium also forms compounds with many other elements. For example, caesium formate is a compound used in oil drilling. It's used because it is very heavy or "dense."

Images for kids

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  High-purity caesium-133 stored in argon.

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  Ball-and-stick model of the cubic coordination of Cs and Cl in CsCl

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  Monatomic caesium halide wires grown inside double-wall carbon nanotubes (TEM image).

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  Cs₁₁O₃ cluster

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  Pollucite, a caesium mineral

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  Gustav Kirchhoff (left) and Robert Bunsen (centre) discovered caesium with their newly invented spectroscope.

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  Atomic clock ensemble at the U.S. Naval Observatory

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  FOCS-1, a continuous cold caesium fountain atomic clock in Switzerland, started operating in 2004 at an uncertainty of one second in 30 million years

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  Caesium chloride powder

See also

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In Spanish: Cesio para niños