Natural boron consists primarily of two stable isotopes, 11B (80.1%) and 10B (19.9%). In nuclear industry boron is commonly used as a neutron absorber due to the high neutron cross-section of isotope 10B. Its (n,alpha) reaction cross-section for thermal neutrons is about 3840 barns (for 0.025 eV neutron). Isotope 11B has absorption cross-section for thermal neutrons about 0.005 barns (for 0.025 eV neutron). Most of (n,alpha) reactions of thermal neutrons are 10B(n,alpha)7Li reactions accompanied by 0.48 MeV gamma emission.
In the United States, 70% of the boron is used for the production of glass and ceramics. The major global industrial-scale use of boron compounds (about 46% of end-use) is in production of glass fiber for boron-containing insulating and structural fiberglasses.
Economically important sources of boron are the minerals colemanite, rasorite (kernite), ulexite and tincal. Together these constitute 90% of mined boron-containing ore.
Protons and Neutrons in Boron
Boron is a chemical element with atomic number 5 which means there are 5 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 Boron are 10; 11.
Main Isotopes of Boron
There are 13 known isotopes of boron, the shortest-lived isotope is 7B which decays through proton emission and alpha decay. It has a half-life of 3.5×10−22 s. Boron has two naturally occurring and stable isotopes, 11B (80.1%) and 10B (19.9%).
Boron-10 is composed of 5 protons, 5 neutrons, and 5 electrons. n nuclear industry boron is commonly used as a neutron absorber due to the high neutron cross-section of isotope 10B. Its (n,alpha) reaction cross-section for thermal neutrons is about 3840 barns (for 0.025 eV neutron). Enriched boron or 10B is used in both radiation shielding and is the primary nuclide used in neutron capture therapy of cancer.
Boron-11 is composed of 5 protons, 6 neutrons, and 5 electrons. Isotope 11B has absorption cross-section for thermal neutrons about 0.005 barns (for 0.025 eV neutron).
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 Boron is 5. 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 Boron is [He] 2s2 2p1.
Possible oxidation states are -5; -1; +1; +2; +3.
Boron normally does not react with acids. In powder form, it reacts with hot nitric acid (HNO 3 ) and hot sulfuric acid (H2SO4 ). It also dissolves in molten (melted) metals. In the most familiar compounds, boron has the formal oxidation state III. These include oxides, sulfides, nitrides, and halides. Boron trifluoride is used in the petrochemical industry as a catalyst. The halides react with water to form boric acid. Boron is found in nature on Earth almost entirely as various oxides of B(III), often associated with other elements. More than one hundred borate minerals contain boron in oxidation state +3.
Most Common Chemical Compound of Boron
Boron carbide (chemical formula approximately B4C) is an extremely hard boron–carbon ceramic and covalent material. It is one of the hardest materials known, ranking third behind diamond and cubic boron nitride. It is the hardest material produced in tonnage quantities. Due to its high hardness, boron carbide powder is used as an abrasive in polishing and lapping applications, and also as a loose abrasive in cutting applications such as water jet cutting.
|Number of protons||5|
|Number of neutrons (typical isotopes)||10; 11|
|Number of electrons||5|
|Electron configuration||[He] 2s2 2p1|
|Oxidation states||-5; -1; +1; +2; +3|
Properties of other elements