Shell octet

Some authors also recommended that the inner-shell octet of a second-row atom should be represented by four doubly occupied FSGOs arranged tetrahe-drally round the nucleus. 

Phosphorus and sulfur are the third-row analogs of nitrogen and oxygen, and the bonding in both can be described using hybrid orbitals. Because of their positions in the third row, however, both phosphorus and sulfur can expand their outer-shell octets and form more than the typical number of covalent bonds. Phosphorus, for instance, often forms five covalent bonds, and sulfur occasionally forms four. 

As a simple but very important example, consider an atom with a valence shell octet of electrons, four of one spin (a electrons) and four of the opposite spin ((3 electrons). 

This arrangement gives the carbon atom a valence shell octet and each H H—C—H... 

Customarily, carbon completes its valence-shell octet by sharing electrons with other atoms. In compounds with shared electron bonds (or covalent bonds) such as methane, ethane, or tetrafluoromethane, each of the bonded atoms including carbon has its valence shell filled, as shown in the following electron-pair or Lewis6 structures ... 

The nitrogen atom in Li3N has an oxidation number of —3 and has gained three electrons over the neutral atom, giving it a valence-shell octet with the neon configuration ... 

Six of the seven valence electrons in a fluorine atom are already paired in three filled atomic orbitals and thus are not shared in bonding. The seventh fluorine valence electron, however, is unpaired and can be used in forming a covalent bond to another fluorine. Each atom in the resultant F2 molecule thereby achieves a filled valence-shell octet. The three pairs of nonbonding electrons on each fluorine atom are called lone pairs, or nonbonded pairs, and the shared electrons are called a bonding pair. 

Group 8A elements (noble gases), such as neon, rarely form covalent bonds because they already have valence-shell octets. 

The number of covalent bonds formed by a main-group element depends on the element s group number. Phosphorus, a group 5A element, has five valence electrons and can achieve a valence-shell octet by forming three bonds and leaving one lone pair. Each hydrogen supplies one electron. 

Boron, having the electronic configuration s22s22p, has 3 valence electrons, and forms planar, tricovalent derivatives that are electron deficient, and which, as Lewis acids, accept two electrons from bases to complete the boron outer-shell octet and give tetrahedral adducts. Boric acid exemplifies this behavior by ionizing, in aqueous solution, not by direct deprotonation, but by hydration and subsequent ionization, to give the symmetrical borate anion ... 

Radicals are highly r ctive because they contain an atom with an odd number of electro-ns (usually aeven) in its valence shell, ratlwr Uian a ata ble noble-gas octet. A radical can achieve a valence-shell octet in several ways. For example, a radical might abstract ii atom from another molecule, leaving behind a new radical. The net result is n radical substituiion reaction ... 

Much chemistry of main group and metal carbonyl species can be rationalized from the way in which these species can achieve closed shell (octet or 18-electron) configurations. These methods of achieving more stable configurations will be illustrated. j for the following electronically equivalent species ... 

Similarly, 6-electron CH2 and 16-electron ML4 are isolobal. Both CH2 andML4 are 2 electrons short of a filled shell octet or 18-electron configuration, so they are electronically equivalent each has 2 single electrons occupying hybrid orbitals at otherwise vacant sites. Absence of a third ligand similarly gives a pair of isolobal fragments, CH and ML3. 

Chemical similarities occur between main group and transition metal species that are electronically equivalent (i.e., species that require the same number of electrons to achieve a filled valence configuration).28 For example, a halogen atom, one electron short of a valence shell octet, may be considered electronically equivalent to Mn(CO)5, a 17-electron species one electron short of an 18-electron configuration. In this section we discuss briefly some parallels between main group atoms and ions and electronically equivalent binary carbonyl complexes. 

Each of these fragments represents the parent polyhedron, with single electrons occupying two hybrid orbitals at otherwise vacant sites each fragment also has two electrons fewer than the filled shell octet or 18-electron configurations. 

Ionic crystals are formed between highly electropositive and highly electronegative elements when electron transfer has occurred between the atoms, resulting in oppositely charged ions with closed shell (octet) electronic configurations. Ionic crystals such as potassium chloride... 

X-ray crystallography and the data show that the complex is not a stannylene derivative, rather the py ligand allows the tin atom to achieve a co-ordination number of four and a valence-shell octet of electrons. ... 

Halogen atoms, one electron short of a valence shell octet, exhibit chemical similarities with 17-electron organometallic species some of the most striking are the parallels between... 

Normally, atoms of elements in the middle of a period of the periodic table, such as carbon or nitrogen atoms, share electrons to form covalent bonds. In methane, CH4, each of 4 H atoms shares an electron with 1C atom, giving each C atom an 8-electron outer shell (octet) like neon (Figure 4.4). Each H atom has 2 electrons, both shared with C, which provides a shell of 2 electrons like that in the noble gas helium. 

As shown in Figure 4.10, when each of the 4 H atoms shares an electron with 1 C atom to form a molecule of methane, CH, each C atom attains an 8-electron outer shell (octet) like neon. Every hydrogen atom attains an outer shell of 2 electrons through the arrangement of shared electrons. There are a total of 4 covalent bonds, 1 per H attached to the C atom, and each composed of a shared pair of electrons. Each of the hydrogen atoms has 2 electrons like the noble gas helium and carbon has an octet of outer shell electrons like the noble gas neon. 

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