Actinium Chemical Properties (25 Facts You Should Know)

Actinium (Ac) is a rare earth metal which is radioactive in nature and has atomic number 89. It is the first element of the actinide series. Let us discuss chemical properties of actinium in detail.

The molar mass of actinium is 227 g/mol. It is radioactive that’s why shines in the dark. Isotopes of actinium is used in radioactive generators. A trace amount of actinium is found in uranium.

Let us discuss the place of actinium in the periodic table, electronegativity, boiling point, melting point, isotopes and many other facts.

Actinium symbol

A chemical symbol is a representation of any element with one or two letters from the latin alphabet. Let us see what is the symbol for actinium.

The symbol of actinium is Ac. The actinide series of the periodic table start with actinium hence the symbol is of the first 2 letters that is ‘Ac’. 

Symbol of Actinium

Actinium group in periodic table

Group of the periodieke tabel represented by column. Let us find the group of actiniums in the periodic table.

Actinium is present in the 3rd group of the periodic table. It is the first element of the actinide series.

Actinium period in periodic table

The horizontal rows represent the period in the periodic table. Let us determine the period of actinium in the periodic table.

Actinium element placed in the 7th periode van die periodieke tabel.

Actinium block in the periodic table

The Block of the periodic table represents the group of elements whose valence electrons are present in the same atomic orbital. Let us see Ac belongs to which block.

Actinium belongs to the ‘d’ block of the periodic table. The valence electron of actinium is present in the d orbital hence it belongs to the d block.

Actinium atomic number

An atomic number of an element is determined based on the number of protons. Let us calculate the atomic number of actinium.

The atomic number of actinium is 89. These many protons are present in the nucleus of actinium.

Actinium atomic weight

Atoomgewig determines the average weight of the element. Which includes the weight of proton, neutron and electrons. Let us find out the atomic weight of actinium.

The atomic weight of actinium is 227 g/mol. Which is the total weight of the proton, electron and neutron.

 Actinium electronegativity according to Pauling

The ability element to attract electrons and form a chemical bond is called elektronegatiwiteit. Let us determine the electronegativity of actinium.

The electronegativity of actinium is 1.1 according to the Pauling scale.

Actinium atomic density

The number of atoms present in the per unit volume of an element is called atomic density. Let us calculate the atomic density of actinium.

The atomic density of actinium is 10.07 g/cm3.

Actinium melting point

 Melting point temperature is a specific temperature at which the solid is converted into a liquid while applying heat. Let us determine the melting point of actinium.

The melting point of actinium is 1227oC. It is a specific temperature at which actinium element melts.

Actinium boiling point

The temperature at which the liquid starts to melt and then vaporized. Let us find out the boiling point of actinium.

The boiling point of actinium is 3200oC. At that temperature, actinium starts boiling and becomes vapourised.

Actinium van der waals radius

Van der waals radius is calculated by the one-half distance of two unbonded atoms. Let us calculate the van der waals radius of actinium.

The van der waals radius of actinium is 215 pm. Which is the one-half distance between two unbonded atoms.

Actinium ionic radius

Ioniese radius is the half distance between the atoms which are barely attached. Let us see the ionic radius of actinium.

The ionic radius of actinium is 0.06Ao. It is a significant distance between the actinides and actinium.

Aktinium isotope

isotope are the two or more forms of elements which is having same atomic mass. Let us see the isotopes of actinium.

Actinium has 32 isotopes from 205Ac to 236Ac. But only 3 isotopes are found in nature these are 225Ac, 226Ac and 227Ac. Following is the table for the most stable isotope of aktinium.

Aktinium isotopeAtoomgetalAtoommassaNumber     of neutronsHalfleeftydverval
Dogter isotoop
225Ac89225.023230 (5)13610 dα221Fr
226Ac89226.026098 (4)13729.37 pmβ, ε, α226Th, 226 Ra, 222Fr
227Ac89227.0277521 (26)13821.772 daarβ, α227ste, 223Fr
Aktinium isotope

Actinium electronic shell

The nucleus of element is surrounded by electrons present in elektroniese skulpe. Let us find out the electronic shell of actinium.

The electronic shell of actinium includes s, p, d, and f shells. Ac has electronic distribution is as follows, 2,2,6,2,6,10,2,6,10,14,2,6,10,2,6,1,2.

Actinium energy of first ionization

eerste ionisasie energy requires for the removal of electrons from the valence orbital from its zero-oxidation state. Let us calculate the energy of the first ionization for actinium.

Actinium requires 5.17eV energy for the first ionization. First ionization removes electrons from the last orbital which contains 1 electron.

Actinium energy of second ionization

Second ionization energy requires the removal of the last orbital electrons or loosely bound electrons from its +1-oxidation state. Let us find 2nd ionization energy of Ac.

Actinium requires 12.1eV energy for the second ionization. Second ionization removes electrons from the loosely bound valence shell.

Actinium energy of third ionization

Third ionisation energy requires the removal of 3 electrons from the outermost orbital of an element from the +2-oxidation state. Let us see 3rd ionisation energy of Ac.

Actinium does not contain 3 electrons in the last outermost orbital. Hence it does not have 3rd ionisasie energie.

Actinium oxidation states

The oxidation state represents the number of electrons lost by the element in the periodic table. Let us determine the oxidation state of Ac.

Actinium shows a +3-oxidation state.

Actinium electron configurations

Electronic configuration determines the distribution of electrons in different orbitals. Let us see the electronic configuration of Ac.

Actinium has 89 electrons which are distributed in different orbitals as follows.

89Ac = [Rn] 6d1 7s2.

Actinium CAS number

CAS number unique code assigned to the chemical as described in scientific literature. Let us see the CAS number of Ac.

Actinium has a CAS number of 7440-34-8.

Actinium ChemSpider ID

ChemSpider ID is a particular number the Royal society of science gives to identify a particular element. Let us see the ChemSpider ID of Ac.

Actinium ChemSpider ID is 22404. Which represents the various properties of actinium in the Royal society of science.

Actinium allotropic forms

allotrope are one or more forms of elements which all have the same physical state. Let us find out the allotropic form of Ac.

Actinium does not contain any allotropic form as they do not exhibit variable oxidation states.

Actinium chemical classification

Chemical classification classifies the elements according to their chemical or physical properties. Let us find out the chemical classification of Ac.

Actinium is classified are as follows.

  • Actinium is a radioactive metal.
  • Actinium is a rare earth metal which mainly occurs in ores of uranium & thorium
  • Ac is a good source of neutrons because it is 150 times as radioactive as radium.

Actinium state at room temperature

Room temperature is an ambient temperature which is referred to as indoor temperature. Which is normally between 20oC na 25oC. Let us see the state of Ac at room temperature.

Actinium is solid at room temperature.

Is actinium paramagnetic?

Paramagnetism is the characteristic in which material gets weekly attracted by an external magnetic field. Let us see whether Ac is paramagnetic or not.

Actinium is paramagnetic in nature. As it has 1 unpaired in the last outermost orbital. The unpaired electron of the 6d orbital makes actinium paramagnetic in nature.


Actinium is the first element of the actinides series. it is a radioactive rare earth metal. Ac has 227 g/mol molar mass, also it is a d block element present in the 7th period. It is paramagnetic in nature.

Darshana Fendarkar

Hi....ek is Darshana Fendarkar, ek het my Ph.D. van die Universiteit van Nagpur. My spesialiteitsgebied is Anorganiese Chemie. Ek het 'n ervaring as 'n chemikus by Earthcare Pvt. Bpk. Ek het ook 2 jaar ondervinding in onderrig. Tans werk ek saam met Lambdageek as vakkundige. Kom ons koppel deur LinkedIn-

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