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Atoms of one element can be transformed into atoms of a different element in nuclear reactions, which change an atom's atomic number. Historically, the term "chemical element" meant a substance that cannot be broken down into constituent substances by chemical reactions, and for most practical purposes this definition still has validity.
Pauling first proposed [3] the concept of electronegativity in 1932 to explain why the covalent bond between two different atoms (A–B) is stronger than the average of the A–A and the B–B bonds. According to valence bond theory , of which Pauling was a notable proponent, this "additional stabilization" of the heteronuclear bond is due to ...
O 2 has a bond length of 121 pm and a bond energy of 498 kJ/mol. [42] O 2 is used by complex forms of life, such as animals, in cellular respiration. Other aspects of O 2 are covered in the remainder of this article. Trioxygen (O 3) is usually known as ozone and is a very reactive allotrope of oxygen that is damaging to lung tissue. [43]
This particle was called the Higgs boson and could be used to test whether the Higgs field was the correct explanation. After a 40-year search , a subatomic particle with the expected properties was discovered in 2012 by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN near Geneva , Switzerland.
Carbon monoxide has a computed fractional bond order of 2.6, indicating that the "third" bond is important but constitutes somewhat less than a full bond. [20] Thus, in valence bond terms, – C≡O + is the most important structure, while :C=O is non-octet, but has a neutral formal charge on each atom and represents the second most important ...
Ammonia boils at −33.34 °C (−28.012 °F) at a pressure of one atmosphere, but the liquid can often be handled in the laboratory without external cooling. Household ammonia or ammonium hydroxide is a solution of ammonia in water.
Particular silicone compounds, cyclic siloxanes D 4 and D 5, are air and water pollutants and have negative health effects on test animals. [31] They are used in various personal care products. The European Chemicals Agency found that "D 4 is a persistent, bioaccumulative and toxic (PBT) substance and D 5 is a very persistent, very ...
[4] [84] In 1995 it was suggested that asteroseismological observations of pulsating white dwarfs yielded a potential test of the crystallization theory, [85] and in 2004, observations were made that suggested approximately 90% of the mass of BPM 37093 had crystallized. [86] [87] [88] Other work gives a crystallized mass fraction of between 32% ...