THE LEWIS ELECTRON-DOT FORMULAS

Since the dipoles are equal and opposite, the vectors of the dipoles cancel out. F. THE LEWIS ELECTRON-DOT FORMULAS 

Lewis Electron-Dot Formulas Lewis electron-dot formulas are diagrammatic representations of the atoms involved and their valence electrons. The valence electrons are usually represented as dots around the elemental symbol. It is a two-dimensional way of representing the structuralformula, showing the bonding electrons and the lone electrons that are in the valence shells. 

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In the water molecule, the central atom is O, and the Lewis electron dot formula predicts that there will be two pairs of nonbonding electrons. The oxygen atom will therefore be tetrahedrally coordinated, even though the number of atoms bound to it is only two. The two nonbonding orbitals are very much like the bonding ones, except that there are no other atoms at their far ends. 

For H2O, the Lewis electron-dot formula suggests the localized MOs to be a pair of equivalent bonding orbitals 6(OHj) and (OHj), an inner-shell Ij oxygen orbital i (0), and two lone-pair equivalent MOs /i(0) and 2(0) on oxygen. 

The Lewis electron-dot formula of a molecule is similar to the structural formula in that it shows how atoms are bonded. Bonding electron pairs are indicated eilher by two dots or by a dash. In addition to the bonding electrons, however, an electron-dot formula shows the positions of lone pairs of electrons, whereas the structural formula does not. Thus, the electron-dot formula is a simple two-dimensional representation of the positions of electrons in a molecule. In the next chapter we will see how to predict the three-dimensional shape of a molecule from the two-dimensional electron-dot formula. In this section we will discuss the steps for writing Ihe electron-dot formula for a molecule made from atoms of the main-group elements. ... 

The next several examples illustrate how to write the Lewis electron-dot formula for a small molecule, given the molecular formula. 

Writing Lewis formulas Given the molecular formula of a simple compound or ion, write the Lewis electron-dot formula. (EXAMPLES 9.6,9.7,93,9.10)... 

Molecular geometries other than trigonal bipyramidal are possible when one or more of the five electron pairs are lone pairs. Consider the sulfur tetrafluoride molecule, SF4. The Lewis electron-dot formula is... 

Step 1 Write the Lewis electron-dot formula of the molecule. 

Have you ever wondered how to draw the structures of compounds For example, compounds such as CCI4, PBr3 or ions such as SO. To draw the structural formulae we will use the Lewis (electron dot) notation. 

Lewis electron-dot structure The Lewis electron-dot structure is a structural formula that represents the element and its valence electrons. 

Le Chatelier s Principle principle that says when a system is at equilibrium and a change is imposed on the system that the system will shift to reduce the change Lewis Electron Dot Formula a diagram showing how the valence electrons are distributed around an atom or distributed in a molecule... 

Ethanol (ethyl alcohol or grain alcohol) has a molecular formula of C2H5OH. Represent the structure of ethanol using the Lewis electron dot approach. 

Lewis electron-dot formulas are simple representations of the valence-shell electrons of atoms in molecules and ions. You can apply simple rules to draw these formulas. In molecules with delocalized bonding, it is not possible to describe accurately the electron distribution with a single Lewis formula. For these molecules, you must use resonance. Although the atoms in Lewis formulas often satisfy the octet rule, exceptions to the octet rule are not uncommon. You can obtain the Lewis formulas for these exceptions by following the rales for writing Lewis formulas. The concept of formal charge will often help you decide which of several Lewis formulas gives the best description of a molecule or ion. 

Write the equations using Lewis electron-dot formulas. Then identify the electron-pair acceptor, or Lewis acid, and the electron-pair donor, or Lewis base. 

Boron trifluoride, BF3, and ammonia, NH3, react to produce BF3 NH3. A coordinate covalent bond is formed between the boron atom on BF3 and the nitrogen atom on NH3. Write the equation for this reaction, using Lewis electron-dot formulas. Label the Lewis acid and the Lewis base. Determine how many grams of BF3 NH3 are formed when 10.0 g BF3 and 10.0 g NH3 are placed in a reaction vessel, assuming that the reaction goes to completion. 

Count the electrons. Count the number of outermost electrons on each of the atoms in the formula before bonding, and add to obtain the total number. This is the number of dots that must be shown in the Lewis electron-dot structure. If the formula is that of a polyatomic ion, also add to this number the extra electrons that are represented by the charge on the ion. 

The same G N Lewis who gave us electron dot formulas also suggested a way of think mg about acids and bases that is more general than the Brpnsted-Lowry approach Where Brpnsted and Lowry viewed acids and bases as donors and acceptors of protons (positively charged) Lewis took the opposite view and focused on electron pairs (negatively charged) According to Lewis an acid is an electron pair acceptor and a base is an electron pair donor... 

Molecular formulas merely include the kinds of atoms and the number of each in a molecule (as C4H , for butane). Structural formulas show the arrangement of atoms in a molecule (see Fig. 1-1). When unshared electrons are included, the latter are called Lewis (electron-dot) structures [see Fig. 1-1(/)]. Covalences of the common elements—the numbers of covalent bonds they usually form—are given in Table 1-1 these help us to write Lewis structures. Multicovalent elements such as C, O. and N may have multiple bonds, as shown in Table 1-2. In condensed structural formulas all H s and branched groups are written immediately after the C atom to which they are attached. Thus the condensed formula for isobutane [Fig. l-l(f>)) is CH,CH(CH,)... 

Lewis structures (Lewis formulas or electron-dot formulas) are two-dimensional pictures of covalent species that show how the atoms are joined together with covalent bonds. A bond is shown as a pair of dots (2 dots = 2 electrons) or a dash (-), which represents a bonding or shared pair of electrons. A single dash represents two shared electrons two dashes (=) represent four shared electrons and so forth. In addition, Lewis structures also show the location of electron pairs not used in bonds, the nonbonding or unshared pairs of electrons. In a correct Lewis structure, all the valence electrons from every atom in the molecule or polyatomic ion must be accounted for, either in bonds or as nonbonding pairs (nb-pairs). 

Use condensed electron configurations and Lewis electron-dot symbols to depict the monatomic ions formed from each of the following atoms, and predict the formula of the compound the ions produce ... 

Most of the time, I use a slight modification of the eiectron-dot formula called the Lewis structural formula it s basically the same as the electron-dot formula, but the shared pair of electrons (the covalent bond) is represented by a dash. The Lewis structural formula is shown in Figure 7-l(c). (Check out the section, Structural formula Add the bonding pattern, for more about writing structural formulas of covalent compounds.)... 

To write a formula that stands for the exact compound you have in mind, you often must write the structural formula instead of the molecular formula. The structural formula shows the elements in the compound, the exact number of each atom in the compound, and the bonding pattern for the compound. The electron-dot formula and Lewis formula are examples of structural formulas. 

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