Chromium is a steely-grey, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point.
Chromium is one of the most important and indispensable industrial metals because of its hardness and resistance to corrosion.
Protons and Neutrons in Chromium
Chromium is a chemical element with atomic number 24 which means there are 24 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 Chromium are 50; 52-54.
Main Isotopes of Chromium
Naturally occurring chromium is composed of three stable isotopes; 52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789% natural abundance).
Chromium-50 is composed of 24 protons, 26 neutrons, and 24 electrons.
Chromium-52 is composed of 24 protons, 28 neutrons, and 24 electrons.
Chromium-53 is composed of 24 protons, 29 neutrons, and 24 electrons.
Chromium-54 is composed of 24 protons, 30 neutrons, and 24 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 Chromium is 24. 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 Chromium is [Ar] 3d5 4s1.
Possible oxidation states are +2,3,6.
Chromium is the first element in the 3d series where the 3d electrons start to sink into the inert core; they thus contribute less to metallic bonding, and hence the melting and boiling points and the enthalpy of atomisation of chromium are lower than those of the preceding element vanadium. Chromium(VI) is a strong oxidising agent in contrast to the molybdenum(VI) and tungsten(VI) oxides. Chromium is a member of group 6, of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.
Most Common Alloy of Chromium
Austenitic stainless steels contain between 16 and 25% Cr and can also contain nitrogen in solution, both of which contribute to their relatively high corrosion resistance. The best known grade is AISI 304 stainless, which contains both chromium (between 15% and 20%) and nickel (between 2% and 10.5%) metals as the main non-iron constituents. 304 stainless steel has excellent resistance to a wide range of atmospheric environments and many corrosive media. These alloys are usually characterized as ductile, weldable, and hardenable by cold forming.
|Number of protons
|Number of neutrons (typical isotopes)
|Number of electrons
|[Ar] 3d5 4s1