Destructive combination

Hybrid orbitals are formed from constructive and destructive combinations of 2p and 2s atomic wave functions, as illustrated by the line plots below. The solid figures depict the corresponding probability functions y2 which describe the electron density in the various directions around the bonded atm. 

Besides, if those m.o.s were occupied, the increased electron density between the nuclei due to constructive combination of 2p orbitals (bonding m.o.) and the corresponding decreased electron density for the destructive combination (anti-bonding m.o.) would occur mainly for regions on opposite sides of the internuclear axis. Hence, the bonding and anti-bonding effects are smaller than for a m.o.s. 

The other MO is formed by combining the two atomic orbitals in a way that causes the electron density to be more or less canceled in the central region where the two overlap. We refer to this as destructive combination. The process is discussed more fully in the Closer Look box later in the chapter we don t need to concern ourselves with it to understand molecular orbital bond formation. The energy of the resulting MO, referred to as the antibonding molecular orbital, is higher than the energy of the atomic orbitals. 

Destructive combination leads to antibonding H2 molecular orbital... 

In picturing the shapes of the resulting hybrid orbitals it may help to remember that orbitals, like waves, can combine constructively or destructively. We can think of the large lobe of each sp hybrid orbital as the result of a constructive combination and the small lobe of each as the result of a destructive combination. 

Remember that the quantum mechanical approach treats atomic orbitals as wave functions[ H Section 6.5], and that one of the properties of waves is their capacity for both constructive combination and destructive combination r W Section 6.1]. 

Atomic orbitals can also combine in a destructive way, canceling each other. The cancellation is similar to the darkness that results when two light waves cancel each other or to the silence that results when two sound waves cancel each other (Figure 1.3b). The destructive combination of two s atomic orbitals is called a a antibonding molecular orbital. An antibonding orbital is indicated by an asterisk ( ), which chemists read as star. Thus, a is read as sigma star. ... 

The next classical pair of destructive steps that was addressed were oxidations and reductions. Here, the oxidant, pyridinium dichromate, and an H2 reduction catalyst RhCl[P(C6H5)3]3 were entrapped in separate silica sol-gel matrices [24], and with these entrapped reagent and catalyst, several different sequences of one-pot redox reaction pairs were carried out - up to four reactions in one pot - without their mutual destruction and with no need for separation steps one of these sequences is shown in Figure 31.10. More mutual destructive combinations are possible, and the last but not least mentioned here is the two-step reaction with a biocatalyst - an enzyme - and an organometallic catalyst, again... 

The destructive combination of the Is atomic orbitals also gives rise to a molecnlar orbital that lies along the intemuclear axis, but, as Figitre 9.11(c) shows, this molecular orbital, which consists of two lobes, does not lie in between the two nuclei. Electron density in this molecular orbital would actually pull the two nuclei in opposite directions, rather than toward each other. This is referred to as an antibonding molecular orbital... 

The non destructive department of Laborelec is mainly involved with problems concerning nuclear, thermal and combined cycle power stations. Our inspections are based on eddy current and ultrasonic testing. 

Valence bond and molecular orbital theory both incorporate the wave description of an atom s electrons into this picture of H2 but m somewhat different ways Both assume that electron waves behave like more familiar waves such as sound and light waves One important property of waves is called interference m physics Constructive interference occurs when two waves combine so as to reinforce each other (m phase) destructive interference occurs when they oppose each other (out of phase) (Figure 2 2) Recall from Section 1 1 that electron waves m atoms are characterized by their wave function which is the same as an orbital For an electron m the most stable state of a hydrogen atom for example this state is defined by the Is wave function and is often called the Is orbital The valence bond model bases the connection between two atoms on the overlap between half filled orbifals of fhe fwo afoms The molecular orbital model assembles a sef of molecular orbifals by combining fhe afomic orbifals of all of fhe atoms m fhe molecule... 

FIGURE 2 2 Interference between waves (a) Constructive interference occurs when two waves combine in phase with each other The amplitude of the resulting wave at each point is the sum of the amplitudes of the original waves (b) Destructive interference decreases the amplitude when two waves are out of phase with each other... 

Termination by combination results in the simultaneous destruction of two radicals by direct coupling ... 

ICP-OES is a destructive technique that provides only elemental composition. However, ICP-OES is relatively insensitive to sample matrix interference effects. Interference effects in ICP-OES are generally less severe than in GFAA, FAA, or ICPMS. Matrix effects are less severe when using the combination of laser ablation and ICP-OES than when a laser microprobe is used for both ablation and excitation. 

Because of the inherently destructive nature of ion bombardment, the use of SSIMS alone in the study of the reactions of surfaces with gases and vapor must be viewed with caution, but in combination with other surface techniques it can provide valuable additional information. The parallel techniques are most often XPS,TDS, and LEED, and the complementary information required from SSIMS normally refers to the nature of molecules on surfaces and with which other atoms, if any, they are combined. 

The different technologies can be used separately or combined, such as gas adsorption followed by incineration. Depending on the system used and the organic compound content in the gas stream being treated, the resulting destruction efficiencies normally range between 90% and 99%. 

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