Carbon atoms valence electrons

Although the nonmetals do not readily form cations, many of them combine with oxygen to form polyatomic oxoanions. These anions have various stoichiometries, but there are some common patterns. Two second-row elements form oxoanions with three oxygen atoms carbon (four valence electrons) forms carbonate, C03, and nitrogen (five valence electrons) forms nitrate, NO3. In the third row, the most stable oxoanions contain four oxygen atoms Si04 -, P04 -, S04, and CI04. ... 

Fig. 4 is a drawing of an all-valence-shell-electron-domain model of ethane superimposed on the molecule s conventional graphic formula. Not shown are the electron-domains of the carbon atoms Is electrons. In Fig. 4, each valence-stroke, i.e. each valence-shell electron-pair of ethane, protonated ("C—H") or unprotonated ( C—C"), is represented by a van der Waals sphere. 

In the case of H2CO3, the single oxygen atom with a free valence is associated with a carbon atom with an incomplete octet on the carbon atom, four electrons from C and three electrons from three separate oxygen atoms, both of which can be resolved by the formation of a double bond between the central carbon atom and the terminal oxygen atom with the free valence ... 

To form organic compounds, the carbon atom shares electrons to give a stable full shell electron configuration of eight valence electrons. 

This image focuses our attention on the continuous system of p orbitals, which functions as a conduit, allowing the two it electrons to be associated with all three carbon atoms. Valence bond theory is inadequate for analysis of this system because it treats the electrons as if they were confined between only two atoms. A more appropriate analysis of the allyl cation requires the use of molecular orbital (MO) theory (Section 1.8), in which electrons are associated with the molecule as a whole, rather than individual atoms. Specifically, in MO theory, the entire molecule is treated as one entity, and all of the electrons in the entire molecule occupy regions of space called molecular orbitals. Two electrons are placed in each orbital, starting with the lowest energy orbital, until all electrons occupy orbitals. 

It also forms compounds known as carbonyls with many metals. The best known is nickel tetracarbonyl, Ni(CO)4, a volatile liquid, clearly covalent. Here, donation of two electrons by each carbon atom brings the nickel valency shell up to that of krypton (28 -E 4 x 2) the structure may be written Ni( <- 0=0)4. (The actual structure is more accurately represented as a resonance hybrid of Ni( <- 0=0)4 and Ni(=C=0)4 with the valency shell of nickel further expanded.) Nickel tetracarbonyl has a tetrahedral configuration,... 

This term is also called the row/coltimn sum (see Figure 2-19). In the example, carbon atom 2 has 1 + 2 -t- 1 = 4 valence electrons. 

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. 

A neutral carbon atom has four valence electrons Five electrons are assigned to the CH2OH carbon therefore it has an oxidation number of -1 Seven electrons are assigned to the CH3 carbon therefore it has an oxidation number of-3 As expected this method gives an oxidation number of -2 for oxygen and +1 for each hydrogen... 

With an atomic number of 28 nickel has the electron conflguration [Ar]4s 3c (ten valence electrons) The 18 electron rule is satisfied by adding to these ten the eight elec Irons from four carbon monoxide ligands A useful point to remember about the 18 electron rule when we discuss some reactions of transition metal complexes is that if the number is less than 18 the metal is considered coordinatively unsaturated and can accept additional ligands... 

In the sodium atom pairs of 3/2 states result from the promotion of the 3s valence electron to any np orbital with n > 2. It is convenient to label the states with this value of n, as n P 1/2 and n f 3/2, the n label being helpful for states that arise when only one electron is promoted and the unpromoted electrons are either in filled orbitals or in an x orbital. The n label can be used, therefore, for hydrogen, the alkali metals, helium and the alkaline earths. In other atoms it is usual to precede the state symbols by the configuration of the electrons in unfilled orbitals, as in the 2p3p state of carbon. 

The chemical shift is related to the part of the electron density contributed by the valence electrons, ft is a natural extension, therefore, to try to relate changes of chemical shift due to neighbouring atoms to the electronegativities of those atoms. A good illustration of this is provided by the X-ray photoelectron carbon Is spectmm of ethyltrifluoroacetate, CF3COOCH2CH3, in Figure 8.14, obtained with AlXa ionizing radiation which was narrowed with a monochromator. 

A second type of hybridisation of the valence electrons in the carbon atom can occur to form three 2sp hybrid orbitals leaving one unhybridised 2p orbital. 

In the third type of hybridisation of the valence electrons of carbon, two linear 2sp orbitals are formed leaving two unhybridised 2p orbitals. Linear a bonds are formed by overlap of the sp hybrid orbitals with orbitals of neighbouring atoms, as in the molecule ethyne (acetylene) C2H2, Fig. 1, A3. The unhybridised p orbitals of the carbon atoms overlap to form two n bonds the bonds formed between two C atoms in this way are represented as Csp Csp, or simply as C C. 

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

Octet rule (Section 1.3) When forming compounds, atoms gain, lose, or share electrons so that the number of their valence electrons is the same as that of the nearest noble gas. For the elements carbon, nitrogen, oxygen, and the halogens, this number is 8. 

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