Californium is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all the elements that have been produced in amounts large enough to see with the unaided eye (after einsteinium). The most commonly used spontaneous fission neutron source is the radioactive isotope californium-252. Cf-252 and all other spontaneous fission neutron sources are produced by irradiating uranium or another transuranic element in a nuclear reactor.
Protons and Neutrons in Californium
Californiumis a chemical element with atomic number98 which means there are 98 protons in its nucleus. Total number of protons in the nucleus is called theatomic numberof the atom and is given thesymbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to1,602 x 10-19coulombs.
The total number ofneutronsin the nucleus of an atom is called theneutronnumberof the atom and is given thesymbol N. Neutronnumber plusatomic numberequals atomic mass number:N+Z=A. The difference between the neutron number and the atomic number is known as theneutron excess: D = N – Z = A – 2Z.
For stable elements, there is usually a variety of stable isotopes. Isotopes are nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons. Mass numbers of typical isotopes of Californiumare248-254.
Main Isotopes of Californium
Californium does not occur in natural isotope.
Naturally Occuring Isotopes
Typical Unstable Isotopes
|248Cf||333.5d||alpha decay or spontaneous fission||244Cm or –|
|249Cf||351 y||alpha decay or spontaneous fission||245Cm or –|
|250Cf||13.08 y||alpha decay or spontaneous fission||246Cm or–|
|251Cf||898 y||alpha decay||247Cm|
|252Cf||2.645y||alpha decay or spontaneous fission||248Cm or–|
|253Cf||17.81d||beta decay or alpha decay||253Es or 249Cm|
|254Cf||16.5 d||spontaneous fission or alpha decay||– or 250Cm|
Electrons and Electron Configuration
The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the number of electrons in neutral atom of Californium is 98. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
Since the number of electrons and their arrangement are responsible for the chemical behavior of atoms, theatomic numberidentifies the various chemical elements. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Electron configuration ofCaliforniumis[Rn] 5f107s2.
Possible oxidation states are+3.
A protonis one of thesubatomic particlesthat make up matter. In the universe, protons are abundant, making upabout halfof all visible matter. It hasa positive electric charge (+1e)and a rest mass equal to 1.67262 × 10−27kg (938.272 MeV/c2)— marginally lighter than that of the neutron but nearly 1836 times greater than that of the electron. The proton has a mean square radius of about 0.87 × 10−15m, or 0.87 fm, and it is a spin – ½ fermion.
The protonsexist in the nuclei of typical atoms, along with their neutral counterparts, the neutrons. Neutrons and protons, commonly callednucleons, are bound together in the atomic nucleus, where they account for 99.9 percent of the atom’s mass. Research in high-energy particle physics in the 20th century revealed that neither the neutron nor the protonis notthe smallest building block of matter.
A neutronis one of thesubatomic particlesthat make up matter. In the universe, neutrons are abundant, making upmore than halfof all visible matter. It hasno electric chargeand a rest mass equal to 1.67493 × 10−27 kg—marginally greater than that of the proton but nearly 1839 times greater than that of the electron. The neutron has a mean square radius of about 0.8×10−15 m, or 0.8 fm, and it is a spin-½ fermion.
Atomic nuclei consist of protons and neutrons, which attract each other throughthe nuclear force, while protons repel each other viathe electric forcedue to their positive charge. These two forces compete, leading to various stability of nuclei. There are only certain combinations of neutrons and protons, which formsstable nuclei.
Neutrons stabilize the nucleus, because they attract each other and protons , which helps offset the electrical repulsion between protons. As a result, as the number of protons increases,an increasing ratio of neutrons to protons is neededto form a stable nucleus. If there are too many or too few neutrons for a given number of protons, the resulting nucleus is not stable and it undergoesradioactive decay.Unstable isotopesdecay through various radioactive decay pathways, most commonly alpha decay, beta decay, or electron capture. Many other rare types of decay, such as spontaneous fission or neutron emission are known. It should be noted that all of these decay pathways may be accompanied bythe subsequent emission ofgamma radiation. Pure alpha or beta decays are very rare.
About Electrons and Electron Configuration
The periodic table is a tabular display of the chemical elements organized on the basis of their atomic numbers, electron configurations, and chemical properties. The electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. Knowledge of theelectron configurationof different atoms is useful in understanding the structure of the periodic table of elements.
Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Thechemical properties of the atomare determined by the number of protons, in fact, by number andarrangement of electrons. Theconfiguration of these electronsfollows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
It is thePauli exclusion principlethat requires the electrons in an atom to occupy different energy levels instead of them all condensing in the ground state. The ordering of the electrons in the ground state of multielectron atoms, starts with the lowest energy state (ground state) and moves progressively from there up the energy scale until each of the atom’s electrons has been assigned a unique set of quantum numbers. This fact has key implications for the building up of the periodic table of elements.
The first two columns on the left side of the periodic table are where thessubshells are being occupied. Because of this, the first two rows of the periodic table are labeled thes block. Similarly, thep blockare the right-most six columns of the periodic table, thed blockis the middle 10 columns of the periodic table, while thef blockis the 14-column section that is normally depicted as detached from the main body of the periodic table. It could be part of the main body, but then the periodic table would be rather long and cumbersome.
For atoms with many electrons, this notation can become lengthy and so an abbreviated notation is used. The electron configuration can be visualized as the core electrons, equivalent to thenoble gasof the preceding period, and the valence electrons (e.g. [Xe] 6s2 for barium).
Oxidation states are typically represented by integers which may be positive, zero, or negative. Most elements have more than one possible oxidation state. For example, carbon has nine possible integer oxidation states from −4 to +4.
The current IUPAC Gold Book definition of oxidation state is:
“Oxidation state of an atom is the charge of this atom after ionic approximation of its heteronuclear bonds…”
and the term oxidation number is nearly synonymous. An element that is not combined with any other different elements has an oxidation state of 0. Oxidation state 0 occurs for all elements – it is simply the element in its elemental form. An atom of an element in a compound will have a positive oxidation state if it has had electrons removed. Similarly, adding electrons results in a negative oxidation state. We have also distinguish between the possible and common oxidation states of every element. For example, silicon has nine possible integer oxidation states from −4 to +4, but only -4, 0 and +4 are common oxidation states.
|Number of protons||98|
|Number of neutrons (typical isotopes)||248-254|
|Number of electrons||98|
|Electron configuration||[Rn] 5f107s2|