Zirconium is a lustrous, grey-white, strong transition metal that resembles hafnium and, to a lesser extent, titanium. Zirconium is mainly used as a refractory and opacifier, although small amounts are used as an alloying agent for its strong resistance to corrosion. Zirconium is widely used as a cladding for nuclear reactor fuels. The desired properties of these alloys are a low neutron-capture cross-section and resistance to corrosion under normal service conditions.
Protons and Neutrons in Zirconium
Zirconium is a chemical element with atomic number 40 which means there are 40 protons in its nucleus. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10-19 coulombs.
The total number of neutrons in the nucleus of an atom is called the neutron number of the atom and is given the symbol N. Neutron number plus atomic number equals atomic mass number: N+Z=A. The difference between the neutron number and the atomic number is known as the neutron 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 Zirconium are 90; 91; 92; 94.
Main Isotopes of Zirconium
Zirconium occurs in 6 natural isotopes: 90Zr, 91Zr, 92Zr, 93Zr, 94Zr and 96Zr. Of these, 96Zr is very slightly radioactive, decaying by double beta decay with a half-life of 2.0×1019 years. 93Zr is a trace radioisotope, decaying by beta decay with a half-life of 1.53×106 years. 90Zr is the most common isotope, having a natural abundance of approximately 51%.
Zirconium-90 is composed of 40 protons, 50 neutrons, and 40 electrons.
Zirconium-91 is composed of 40 protons, 51 neutrons, and 40 electrons.
Zirconium-92 is composed of 40 protons, 52 neutrons, and 40 electrons.
Zirconium-93 is composed of 40 protons, 53 neutrons, and 40 electrons.
Zirconium-94 is composed of 40 protons, 54 neutrons, and 40 electrons.
Zirconium-96 is composed of 40 protons, 56 neutrons, and 40 electrons.
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 Zirconium is 40. 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, the atomic number identifies 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 of Zirconium is [Kr] 4d2 5s2.
Possible oxidation states are +4.
Most Common Alloys of Zirconium
Zirconium alloyed with niobium or tin has excellent corrosion properties. The high corrosion resistance of zirconium alloys results from the natural formation of a dense stable oxide on the surface of the metal. Zirconium alloys, in which tin is the basic alloying element, provide improvement of their mechanical properties, and have a wide distribution in the USA. A common subgroup has the trade mark Zircaloy.
|Number of protons
|Number of neutrons (typical isotopes)
|90; 91; 92; 94
|Number of electrons
|[Kr] 4d2 5s2