Six valence electrons

The structure of diborane B2H6 is considered later (p. 145). Here we may note that "BHj and "AlHj will be acceptor molecules since there are only six valency electrons around the B or A1 atom and a vacant orbital exists. Both in fact can accept the electron pair from a hydride ion thus ... 

Trivalent ( classical carbenium ions contain an sp -hybridized electron-deficient carbon atom, which tends to be planar in the absence of constraining skeletal rigidity or steric interference. The carbenium carbon contains six valence electrons thus it is highly electron deficient. The structure of trivalent carbocations can always be adequately described by using only two-electron two-center bonds (Lewis valence bond structures). CH3 is the parent for trivalent ions. 

The properties of tert butyl cation can be understood by focusing on its structure which IS shown m Figure 4 9 With only six valence electrons which are distributed among three coplanar ct bonds the positively charged carbon is sp hybridized The unhybridized 2p orbital that remains on the positively charged carbon contains no elec Irons Its axis is perpendicular to the plane of the bonds connecting that carbon to the three methyl groups... 

Iodomethylzinc iodide is often refened to as a carbenoid, meaning that it resembles a carbene in its chemical reactions. Caibenes are neutral molecules in which one of the caibon atoms has six valence electrons. Such caibons aie divalent they are directly bonded to only two other atoms and have no multiple bonds. Iodomethylzinc iodide reacts as if it were a source of the caibene H—C—H. 

Fenocene has an even more interesting stmcture. A central iron is ir-bonded to two cyclopentadienyl ligands in what is aptly described as a sandwich. It, too, obeys the 18-electron rule. Each cyclopentadienyl ligand contributes five electrons for a total of ten and iron, with an electron configuration of [Ar]45 34i contributes eight. Alternatively, fenocene can be viewed as being derived from Fe " (six valence electrons) and two aromatic cyclopentadienide rings (six electrons each). 

Carbene (Section 14.13) A neutral species in which one of the carbon atoms is associated with six valence electrons. 

This difference is due to the two lone pairs on the oxygen. Of the six valence electrons on the oxygen atom, two are involved in the double bond with the carbon, and the other four exist as two lone pairs. In Chapter 4, we ll examine the IR spectra for these two molecules. The orbitals suggest that we ll find very different frequencies for the two systems. In Chapter 9, we ll look at the transition to the first excited state in formaldehyde. ... 

Methylene (CH2) has six valence electrons. Four are needed for the two CH bonds. Possibilities for the other two include ... 

The neutral divalent carbon atom of a carbene, CX2, with its six valency electrons is electron deficient and hence electrophilic. The... 

The number of covalent bonds an atom forms depends on how many additional valence electrons it needs to reach a noble-gas configuration. Hydrogen has one valence electron (Is) and needs one more to reach the helium configuration (Is2), so it forms one bond. Carbon has four valence electrons (2s2 2p2) and needs four more to reach the neon configuration (2s2 2p6), so it forms four bonds. Nitrogen has five valence electrons (2s2 2p3), needs three more, and forms three bonds oxygen has six valence electrons (2s2 2p4), needs two more, and forms two bonds and the halogens have seven valence electrons, need one more, and form one bond. 

A great deal of evidence has shown that carbocations are planar. The divalent carbon is 5p2-hybridized, and the three substituents are oriented to the corners of an equilateral triangle, as indicated in Figure 6.9. Because there are only six valence electrons on carbon and all six are used in the three a bonds, the p orbital extending above and below the plane is unoccupied. 

A carbene, R2C , is a neutral molecule containing a divalent carbon with only six valence electrons. Carbenes are highly reactive toward alkenes, adding to give cyclopropanes. Nonlialogenated cyclopropanes are best prepared by treatment of the alkene with CH212 and zinc-copper, a process called the Simmons-Smith reaction. 

As you can see, the fluorine atom owns six valence electrons outright and shares two others. Putting it another way, the F atom is surrounded by eight valence electrons its electron configuration has become ls22s22p6, which is that of the noble gas neon. This, according to Lewis, explains why the HF molecule is stable in contrast to species such as H2F, H3F,... none of which exist. 

The extra electron pairs in an expanded octet are accommodated by using d orbitals. The phosphorus atom (five valence electrons) in PC15 and the sulfur atom (six valence electrons) in SF6 make use of 3d as well as 3s and 3p orbitals ... 

Consider the dichromate ion. It has no metal-metal nor oxygen-oxygen bonds. Write a Lewis structure for die dichromate ion. Consider chromium to have six valence electrons. 

The neutral oxygen atom has eight electrons. Six of these occupy the 2s, 2p orbitals and are much more easily removed than the two in the Is orbital. Therefore oxygen has six valence electrons. The 2s, 2p orbitals are the valence orbitals. They can accommodate the valence electrons in two ways, as follows ... 

The III-V and II-VI compounds refer to combination of elements that have two, three, five, or six valence electrons. They have semiconductor properties and are all produced by CVD either experimentally or in production. The CVD of these materials is reviewed in Ch. 12. Many of their applications are found in optoelectronics where they are used instead of silicon, since they have excellent optical properties (see Ch. 15). Generally silicon is not a satisfactory optical material, since it emits and absorbs radiation mostly in the range of heat instead of light. 

Let s begin by determining the number of valence electrons that an oxygen atom is supposed to have. Oxygen is in Column 6A of the periodic table, so oxygen should have six valence electrons. Next, we need to look at the oxygen atom in this compound and ask how many valence electrons it actually has. So, we redraw the stuc-ture by splitting up the C-0 bond ... 

Sulfur, in Group 16, has six valence electrons. The configurations show six electrons with = 3, so the configuration is consistent with the valence electron count. The electrons are spread among the three 3 p orbitals, which minimizes electron-electron repulsion. 

The concept of an octet of electrons is one of the foundations of chemical bonding. In fact, C, N, and O, the three elements that occur most frequently in organic and biological molecules, rarely stray from the pattern of octets. Nevertheless, an octet of electrons does not guarantee that an inner atom is in its most stable configuration. In particular, elements that occupy the third and higher rows of the periodic table and have more than four valence electrons may be most stable with more than an octet of electrons. Atoms of these elements have valence d orbitals, which allow them to accommodate more than eight electrons. In the third row, phosphoms, with five valence electrons, can form as many as five bonds. Sulfur, with six valence electrons, can form six bonds, and chlorine, with seven valence electrons, can form as many as seven bonds. 

All three atoms are from Group 16 of the periodic table, so each has six valence electrons, giving 18 for the molecule. 

Because sulfur is from row 3, we determine how to optimize the structure by evaluating formal charge. Sulfur has six valence electrons (Group 16) and four assigned electrons (2 bonds + 2 lone-pair electrons) ... 

The phosphoms atom contributes five valence electrons, the four oxygen atoms contribute six valence electrons each, and the hydrogen atoms each contribute one electron. The negative charge indicates that there is an extra electron, for a total of 32 valence electrons. 

Borane, BH3, having only six valence electrons on boron, is an avid electron pair acceptor. Pure borane exists as a dimer in which two hydrogens bridge the borons. 

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