Pyramidal shape

Because of the pyramidal shape in these excited states the orbitals and states may be reclassified according to the Q point group (Table A. 1 in Appendix A). 

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

Oxides. Two oxides of xenon are known xenon trioxide [13776-58-4], XeO, and xenon tetroxide [12340-14-6], XeO (Table 1). Xenon trioxide is most efftcientiy prepared by the hydrolysis of XeE (47) or by the reaction of XeE with HOPOE2 (48). The XeO molecule has a trigonal pyramidal shape Xe—O, 176(3) pm (49), and XeO is tetrahedral with Xe—O, 173.6(2) pm (50). Xenon tetroxide is prepared by the interaction of concentrated sulfuric acid with sodium or barium perxenate, Na XeO, Ba2XeO ( )- Both oxides are thermodynamically unstable, explosive soHds which must be... 

Hardness is determined by measuring the penetration (depth or area) when a harder material, such as diamond, is pushed into the surface of the material of interest under a specified load. Tme hardness is defined as the force divided by the projected area. Vickers hardness tests, which employ a pyramid-shaped indentor, are frequently used to characterize ceramics however, Vickers hardness calculations normally employ total surface area rather than projected area (43). Measurements are made on the diamond impression shown in Figure 6. Vickers hardness is calculated using... 

There are a number of important kinds of stereogenic centers besides asymmetric carbon atoms. One example is furnished by sulfoxides with nonidentical substituents on sulfur. Sulfoxides are pyramidal and maintain dieir configuration at room temperature. Unsymmetrical sulfoxides are therefore chiral and exist as enantiomers. Sulfonium salts with three nonidentical ligands are also chiral as a result of their pyramidal shape. Some examples of chiral derivatives of sulfur are given in Scheme 2.1. 

Another variation is to use a pyramid-shaped tank at grade level with an inclined dewatering screw feeder. Refer to Figure 38 for an example. Tank materials are usually constructed from carbons steel, stainless steel, stainless clad, resin or epoxy-lined for those situations where iron contamination in the product is a concern, or if corrosion by the adsorbate in the carbon is possible. 

Pyramidal neurons are the principal long-projecting cells of the cerebral cortex and hippocampus. They are so named because of the characteristic large apical dendrite, giving them a pyramidal shape. 

Note that only when using the type of representation on the right do we show the lone pair explicitly. Spectroscopic measurements confirm the prediction of a trigonal pyramidal shape for NF . 

Ankyrin is a pyramid-shaped protein that binds spectrin. In mrn, ankyrin binds tightly to band 3, securing attachment of spectrin to the membrane. Ankyrin is sensitive to proteolysis, accounting for the appearance of bands 2.2, 2.3, and 2.6, all of which are derived from band 2.1. 

Many of the diamondoids can be brought to macroscopic crystalline forms with some special properties. For example, in its crystalline lattice, the pyramidal-shaped [l(2,3)4]pentamantane (see Table I) has a large void in comparison to similar crystals. Although it has a diamond-like macroscopic structure, it possesses the weak, noncovalent, intermolecular van der Waals... 

Chlorine pentafluoride and xenon tetrafluoride appear in Figure 9-26. Each has an inner atom with a steric number of 6, but their electron group arrangements include lone pairs. As a result, CIF5 has a square pyramidal shape, whereas XeF4 has a square planar shape. Pictures can help us determine whether or not the bond polarities cancel ... 

Remember that the molecular shape ignores the lone pair. The hydronium ion has a trigonal pyramidal shape described by the three s p hybrid orbitals that form bonds to hydrogen atoms. 

Figure 1.33 The tetrahedral arrangement of the electron pairs of an ammonia molecule that results when the nonbonding electron pair is considered to occupy one corner. This arrangement of electron pairs explains the trigonal pyramidal shape of the NH3 molecule.

Based on their microwave digestion system, Milestone offers the MicroSYNTH labstation (also known as ETHOS series) multimode instrument (Fig. 3.4 and Table 3.1), which is available with various accessories. Two magnetrons deliver 1000 W microwave output power and a patented pyramid-shaped microwave diffuser ensures homogeneous microwave distribution within the cavity [12]. 

The free selenite ion has a pyramidal shape (C3v symmetry) owing to the lone electron pair at the selenium atom. Thus, the Se032- ion can be treated as a pseudo-tetrahedral anion and the lone electron pair often acts as an invisible ligand within the crystal structures of selenites. This observation is called the stereochemical activity of the lone electron pair and it will turn out as one of the... 

A new structure type is found for Ag2Hg(Se03)2. Both Ag+ and Hg2+ ions are in octahedral coordination in this compound.137 The polyhedra are linked by the pyramidal shaped selenite anions.138 In the crystal structure of the red tellurate Ag2Hg2(Te04)3, the tellurium atoms are in octahedral coordination of oxygen atoms, and the octahedra are linked to infinite chains running along the u-axis. 

Three bond pairs and one lone pair (1). To maximise the separation between the electron pairs, a trigonal pyramidal shape is adopted (1). H PH bond angle <109.5°, because lone pair/bond pair repulsion is greater than bond pair/bond pair repulsion. 

The unique interhybrid angle in this case is 90° (aacute = obtuse), leading to a trigonal pyramidal shape of C3V symmetry ... 

Pears can be grown as a pyramid-shaped tree with a central trunk or, as apples are, as a low-branching bush tree. They can also be trained Into two-dimensional shapes such as cordons... 

The shape of a molecule or ion is governed by the shape adopted by its constituent atoms. In PHj, for example, there are four electron pairs, but three of them are bonded pairs and one is a non-bonded pair. The four electron pairs adopt a tetrahedral shape but the three bonded pairs adopt a pyramidal shape. So the PHj molecule is described as pyramidal, not tetrahedral. As the base of this pyramidal structure is triangular rather than, say, square, the shape is more correctly referred to as trigonal pyramidal. 

Note A lamellar crystal is usually of a thickness in the 5-50 nm range, and it may be found individually or in aggregates. The parallel-chain stems intersect the lamellar plane at an angle between 45° and 90°. The lamellae often have pyramidal shape owing to differences in the fold domains, as a result, one can deduce different fold planes and fold surfaces from the lamellar morphology. 

Ammonia, (NH3) has a pyramidal shape. Methane, (CH4) has a tetrahedral shape. 

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