In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name since it does not contain any words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulae can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than chemical names and structural formulae.
Diatomic molecules are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen or oxygen, then it is said to be homonuclear. Otherwise, if a diatomic molecule consists of two different atoms, such as carbon monoxide or nitric oxide, the molecule is said to be heteronuclear. The bond in a homonuclear diatomic molecule is non-polar.
The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.
The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The rule is especially applicable to carbon, nitrogen, oxygen, and the halogens; although more generally the rule is applicable for the s-block and p-block of the periodic table. Other rules exist for other elements, such as the duplet rule for hydrogen and helium, and the 18-electron rule for transition metals.
In chemistry, a hypervalent molecule is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pentachloride, sulfur hexafluoride, chlorine trifluoride, the chlorite ion, and the triiodide ion are examples of hypervalent molecules.
In chemistry, an interhalogen compound is a molecule which contains two or more different halogen atoms and no atoms of elements from any other group.
In chemistry, the valence or valency of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Valence is generally understood to be the number of chemical bonds that each atom of a given element typically forms. For a specified compound the valence of an atom is the number of bonds formed by the atom. Double bonds are considered to be two bonds, and triple bonds to be three. In most compounds, the valence of hydrogen is 1, of oxygen is 2, of nitrogen is 3, and of carbon is 4. Valence is not to be confused with the related concepts of the coordination number, the oxidation state, or the number of valence electrons for a given atom.
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides/oxychlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.
In chemistry, a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not identical, because there is no geometrical arrangement with five terminal atoms in equivalent positions. Examples of this molecular geometry are phosphorus pentafluoride, and phosphorus pentachloride in the gas phase.
Chlorine monofluoride is a volatile interhalogen compound with the chemical formula ClF. It is a colourless gas at room temperature and is stable even at high temperatures. When cooled to −100 °C, ClF condenses as a pale yellow liquid. Many of its properties are intermediate between its parent halogens, Cl2 and F2.
Phosphorus pentafluoride, PF5, is a phosphorus halide. It is a colourless, toxic gas that fumes in air.
A-values are numerical values used in the determination of the most stable orientation of atoms in a molecule, as well as a general representation of steric bulk. A-values are derived from energy measurements of the different cyclohexane conformations of a monosubstituted cyclohexane chemical. Substituents on a cyclohexane ring prefer to reside in the equatorial position to the axial. The difference in Gibbs free energy (ΔG) between the higher energy conformation and the lower energy conformation is the A-value for that particular substituent.
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers.
Thionyl tetrafluoride, also known as sulfur tetrafluoride oxide, is an inorganic compound with the formula SOF4. It is a colorless gas.
Chlorine peroxide is a molecular compound with formula ClOOCl. Chemically, it is a dimer of the chlorine monoxide radical (ClO·). It is important in the formation of the ozone hole. Chlorine peroxide catalytically converts ozone into oxygen when it is irradiated by ultraviolet light.
Chlorotrifluorosilane is an inorganic gaseous compound with formula SiClF3 composed of silicon, fluorine and chlorine. It is a silane that substitutes hydrogen with fluorine and chlorine atoms.
Pentamethylantimony or pentamethylstiborane is an organometalllic compound containing five methyl groups bound to an antimony atom with formula Sb(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramid. Some other antimony(V) organometallic compounds include pentapropynylantimony (Sb(CCCH3)5) and pentaphenyl antimony (Sb(C6H5)5). Other known pentamethyl-pnictides include pentamethylbismuth and pentamethylarsenic.
Cyanophosphaethyne is an unstable molecular compound with structural formula N≡C–C≡P. It can be considered as cyanogen with one nitrogen atom replaced by phosphorus. It has been made as a dilute gas. Cyanophosphaethyne has been tentatively detected in the interstellar medium. Other structural isomers, such as C≡N–C≡P (isocyanophosphapropyne), C≡C-N≡P (azaphosphadicarbon), and N≡C–P=C (isocyanophosphavinylidene), have not been observed. The molecule has linear molecular geometry.
Phosphorus monoxide is an unstable radical inorganic compound with molecular formula PO.
Linnett double-quartet theory (LDQ) is a method of describing the bonding in molecules which involves separating the electrons depending on their spin, placing them into separate 'spin tetrahedra' to minimise the Pauli repulsions between electrons of the same spin. Introduced by J. W. Linnett in his 1961 monograph and 1964 book, this method expands on the electron dot structures pioneered by G. N. Lewis. While the theory retains the requirement for fulfilling the octet rule, it dispenses with the need to force electrons into coincident pairs. Instead, the theory stipulates that the four electrons of a given spin should maximise the distances between each other, resulting in a net tetrahedral electronic arrangement that is the fundamental molecular building block of the theory.
