Electrons octet rule

Carbocation has a positively charged carbon atom which has only six electrons in its outer valence shell instead of the eight valence electrons (octet rule). 

Dalton s atomic theory Electron shells Inner shell electrons Octet rule... 

When atoms form covalent bonds, they try to attain a valence-electron configuration similar to that of the following noble gas element. When the elements in the first few horizontal rows of the periodic table form covalent bonds, they attempt to achieve the configurations of the noble gases helium (two valence electrons, duet rule) and neon and argon (eight valence electrons, octet rule). 

In the example in Figure 2-19, the oxygen atom 3 has 2- 4 (row) + 2 + 4 (column) - 4 (diagonal element) = 8 electrons. This shows that the ox> gen atom obeys the octet rule. 

Figure 2-19. The BE-matriK of ethanal allows one to determine tine number of valence electrons (the sum of each row) on the atoms and to validate the octet rule,...

Protonated methane (CH ) does not violate the octet rule of carbon. A bonding electron pair (responsible for covalent bonding between C and H atoms) is forced into sharing with the proton, resulting in 2 electron-3 center bonding (2e-3c) (see Chapter 10). Higher alkanes are protonated similarly. 

Lewis s concept of shared electron parr bonds allows for four electron double bonds and SIX electron triple bonds Carbon dioxide (CO2) has two carbon-oxygen double bonds and the octet rule is satisfied for both carbon and oxygen Similarly the most stable Lewis structure for hydrogen cyanide (HCN) has a carbon-nitrogen triple bond... 

Lewis structures in which second row elements own or share more than eight valence electrons are especially unstable and make no contribution to the true structure (The octet rule may be ex ceeded for elements beyond the second row)... 

Section 1 3 The most common kind of bonding involving carbon is covalent bond ing A covalent bond is the sharing of a pair of electrons between two atoms Lewis structures are written on the basis of the octet rule, which limits second row elements to no more than eight electrons m their valence shells In most of its compounds carbon has four bonds... 

There is ample evidence from a variety of sources that carbocations are mterme diates m some chemical reactions but they are almost always too unstable to isolate The simplest reason for the instability of carbocations is that the positively charged car bon has only six electrons m its valence shell—the octet rule is not satisfied for the pos itively charged carbon... 

Free radicals are species that contain unpaired electrons The octet rule notwithstand mg not all compounds have all of their electrons paired Oxygen (O2) is the most famil lar example of a compound with unpaired electrons it has two of them Compounds that have an odd number of electrons such as nitrogen dioxide (NO2) must have at least one unpaired electron... 

Of the two resonance forms A and B A has only six electrons around its positively charged carbon B satisfies the octet rule for both carbon and oxygen It is more stable than A and more stable than a carbocation formed by protonation of a typical alkene... 

Many transition metal complexes including Ni(CO)4 obey the 18 electron rule, which IS to transition metal complexes as the octet rule is to mam group elements like carbon and oxygen It states that... 

Lewis structure (Section 1 3) A chemical formula in which electrons are represented by dots Two dots (or a line) be tween two atoms represent a covalent bond in a Lewis structure Unshared electrons are explicitly shown and sta ble Lewis structures are those in which the octet rule is sat isfied... 

Octet rule (Section 1 3) When forming compounds atoms gain lose or share electrons so that the number of their va lence electrons is the same as that of the nearest noble gas For the elements carbon nitrogen oxygen and the halo gens this number is 8... 

Note that these compounds are covalently bonded compounds containing only hydrogen and carbon. The differences in their strucmral formulas are apparent the alkanes have only single bonds in their structural formulas, while the alkenes have one (and only one) double bond in their structural formulas. There are different numbers of hydrogen atoms in the two analogous series. This difference is due to the octet rule that carbon must satisfy. Since one pair of carbon atoms shares a double bond, this fact reduces the number of electrons the carbons need (collectively) by two, so there are two fewer hydrogen atoms in the alkene than in the corresponding alkane. 

Beryllium forms a series of cyclopentadienyl complexes [Beftj -CsHiY] with Y = H, Cl, Br, Me, —C=CH and BH4, all of which show the expected C5, symmetry (Fig. 5.10a). If the pe/ifo/topfo-cyclopentadienyl group (p. 937) contributes 5 electrons to the bonding, then these are all 8-electron Be complexes consistent with the octet rule for elements of the first short... 

Rule 4 Resonance forms obey norma] rules of valency. A resonance form is like any other structure the octet rule still applies to main-group atoms. For example, one of the following structures for the acetate ion is not a valid resonance form because the carbon atom has five bonds and ten valence electrons ... 

The octet rule must be followed. That is, no second-row atom can be left with ten electrons (or four for hydrogen). If an electron pair moves to an atom that already has an octet (or two for hydrogen), another electron pair must simultaneously move from that atom to maintain the octet. When two electrons move from the C=C bond of ethylene to the hydrogen atom of for... 

First, look at the reaction and identify the bonding changes that have occurred. In this case, a C—Br bond has broken and a C-C bond has formed. The formation of the C-C bond involves donation of an electron pair from the nucleophilic carbon atom of the reactant on the left to the electrophilic carbon atom ol CH Br, so we draw a curved arrow originating from the lone pair on the negatively charged C atom and pointing to the C atom of CH3Br. At the same time the C—C bond forms, the C-Br bond must break so that the octet rule is not violated. We therefore draw a second curved arrow from the C-Br bond to Br. The bromine is now a stable Br- ion. 

These examples illustrate the principle that atoms in covalently bonded species tend to have noble-gas electronic structures. This generalization is often referred to as the octet rule. Nonmetals, except for hydrogen, achieve a noble-gas structure by sharing in an octet of electrons (eight). Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two). 

Reality Check Whenever you write a Lewis structure, check to see if it follows the octet rule. The structures written for OCl and C2H6 do just that each atom except H is surrounded by eight electrons. 

Exceptions to the Octet Rule Electron-Deficient Molecules... 

Although most of the molecules and polyatomic ions referred to in general chemistry follow the octet rule, there are some familiar species that do not. Among these are molecules containing an odd number of valence electrons. Nitric oxide, NO, and nitrogen dioxide, N02, fall in this category ... 

For such odd electron species (sometimes called free radicals) it is impossible to write Lewis structures in which each atom obeys the octet rule. In the NO molecule, the unpaired electron is put on the nitrogen atom, giving both atoms a formal charge of zero ... 

There are a few species in which the central atom violates the octet rule in the sense that it is surrounded by two or three electron pairs rather than four. Examples include the fluorides of beryllium and boron, BeF2 and BF3. Although one could write multiple bonded structures for these molecules in accordance with the octet rule (liable 7.2), experimental evidence suggests the structures... 

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