Lewis structures of atoms

Periodic relationship of the first ionization energy for representative elements in the first four periods. 

The valence electrons in the outermost energy level of an atom are responsible for the electron activity that occurs to form chemical bonds. The Lewis structure of an atom is a representation that shows the valence electrons for that atom. American chemist Gilbert N. Lewis (1875-1946) proposed using the symbol for the element and dots for electrons. The number of dots placed around the symbol equals the number of s and p electrons in the outermost energy level of the atom. Paired dots represent paired electrons unpaired dots represent unpaired electrons. For example, H is the Lewis symbol for a hydrogen atom, Is B is the Lewis symbol for a boron atom, with valence electrons 2s 2p In the case of boron, the symbol B represents the boron nucleus and the Is electrons the dots represent only the 2s 2p electrons. 

Lewis structures of the first 20 elements. Dots represent electrons in the outermost s and p energy levels only. 

A quick way to determine the correct number of dots (eiectrons) for a Lewis structure is to use the Group number. For the A groups on the periodic tabie, the Group number is the same as the number of eiectrons in the Lewis structure. 

First establish the electron structure for a phosphorus atom, which is ls 2s 2p 3s 3p. Note that there are five electrons in the outermost energy level they are 3s 3p. Write the symbol for phosphorus and place the five electrons as dots around it. 

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Lewis Structures of Atoms Commonly Forming Covalent Bonds... 

Structural formula J is a Lewis structure of nitro methane K is not even though it has the same atomic positions and the same number of electrons... 

Electron Delocalization in the Conjugate Base With a of —1 4 nitnc acid is almost completely ionized m water If we look at the Lewis structure of nitric acid m light of what we have said about inductive effects we can see why The N atom m nitric acid IS not only electronegative m its own right but bears a formal charge of +1 which enhances its ability to attract electrons away from the —OH group... 

Since nucleophilic atoms have nonbonding electrons they can be identified by inspection of Lewis structures. Draw Lewis structures of triraethylamine, methyl fluoride, and phenol. Draw all nonbonding electron pairs and identify all nucleophilic atoms. 

Obtain the energies of the different possible carbanions alleyne-H+). Which one is most stable Does it correspond to removal of the most electron-poor proton Examine the geometry and atomic charges of the favored carbanion. Where is the negative charge Draw the Lewis structure of this ion. Predict the structure of the Sn2 product. 

Compare geometries, atomic charges and electrostatic potential maps of thionyl chloride and phosphorus trichloride. How are they similar How are they different Can you redraw the Lewis structure of SOCI2 so that it gives abetter description of the electrostatic potential map ... 

Sixteen electrons are required to give each atom an octet (four for S and six for each O). There is a deficiency of two electrons. This means that a single bond in the skeleton must be converted to a double bond. The Lewis structure of S02 is... 

The largest class of molecules to violate the octet rule consists of species in which the central atom is surrounded by more than four pairs of valence electrons. Typical molecules of this type are phosphorus pentachloride, PC15, and sulfur hexafluoride, SF6. The Lewis structures of these molecules are... 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

In many expanded-octet molecules, one or more of the electron pairs around the central atom are unshared. Recall, for example, the Lewis structure of xenon tetrafluoride, XeF4 (Example 7.4). 

The Lewis structures of the oxides of nitrogen are shown in Figure 21.6. Two of these species, NO and NO are paramagnetic, with one impaired electron. When nitrogen dioxide is cooled, it dimerizes the unpaired electrons combine to form a single bond between the two nitrogen atoms ... 

The Lewis structure of a molecule shows atoms by their chemical symbols, covalent bonds by lines, and lone pairs by pairs of dots. For example, the Lewis structure of HF is H - F . We shall see that Lewis structures are a great help in... 

The Lewis structure of a polyatomic species is obtained by using all the valence electrons to complete the octets (or duplets) of the atoms present by forming single or multiple bonds and leaving some electrons as lone pairs. 

Seif-Test 2.1 IB Calculate the formal charges for the three oxygen atoms in one of the Lewis structures of the ozone resonance structure (Example 2.5). 

The Lewis structure of the product, a white molecular solid, is shown in (32). In this reaction, the lone pair on the nitrogen atom of ammonia, H3N , can be regarded as completing boron s octet in BF3 by forming a coordinate covalent bond. 

Two contributions to the resonance structure are shown below for each species. Determine the formal charge on each atom and then, if possible, identify the Lewis structure of lower energy for each species. 

Quinone, C6H4On is an organic molecule with the structure shown below it can be reduced to the anion C(iI l4Or. (a) Draw the Lewis structure of the reduced product, (b) On the basis of formal charges derived from the Lewis structure, predict which atoms in the molecule are most negatively charged, (c) If two protons are added to the reduced product, where are they most likely to bond ... 

Now consider the alkynes, hydrocarbons with carbon-carbon triple bonds. The Lewis structure of the linear molecule ethyne (acetylene) is H—O C- H. To describe the bonding in a linear molecule, we need a hybridization scheme that produces two equivalent orbitals at 180° from each other this is sp hybridization. Each C atom has one electron in each of its two sp hybrid orbitals and one electron in each of its two perpendicular unhybridized 2p-orbitals (43). The electrons in the sp hybrid orbitals on the two carbon atoms pair and form a carbon—carbon tr-bond. The electrons in the remaining sp hybrid orbitals pair with hydrogen Ls-elec-trons to form two carbon—hydrogen o-bonds. The electrons in the two perpendicular sets of 2/z-orbitals pair with a side-by-side overlap, forming two ir-honds at 90° to each other. As in the N2 molecule, the electron density in the o-bonds forms a cylinder about the C—C bond axis. The resulting bonding pattern is shown in Fig. 3.23. 

Acrylonitrile, CH,CHCN, is used in the synthesis of acrylic fibers (polyacrylonitriles), such as Orion. Write the Lewis structure of acrylonitrile and describe the hybrid orbitals on each carbon atom. What are the approximate values of the bond angles ... 

The Lewis structure of caffeine, C8H 0N4O2, a common stimulant, is shown below, (a) Give the hybridization of each atom other than hydrogen and predict the bond angles about that atom, (b) On the basis of your answers in part (a), estimate the bond angles around each carbon and nitrogen atom. 

A student wrote the formula I IN instead of Nil, on in examination by mistake, (a) Write the name and Lewis structure of the compound corresponding to the formula the student wrote (the N atoms are connected in a chain and the... 

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