Lewis structures drawing rules

Using only Lewis structures that obey the octet rule, draw the Lewis structures and determine the formal charge on each atom in (a) CHsf (b) OCL (c) BF4". 

White phosphorus is composed of tetrahedral molecules of P4 in which each P atom is connected to three other P atoms. Draw the Lewis structure for this molecule. Does it obey the octet rule ... 

For each molecule, ion, or free radical that has only localized electrons, it is possible to draw an electronic formula, called a Lewis structure, that shows the location of these electrons. Only the valence electrons are shown. Valence electrons may be found in covalent bonds connecting two atoms or they may be unshared. The student must be able to draw these structures correctly, since the position of electrons changes in the course of a reaction, and it is necessary to know where the electrons are initially before one can follow where they are going. To this end, the following rules operate ... 

The rules used to draw Lewis structures are as follows ... 

Even though we have an exception, we can still complete the Lewis structure. We need to draw a bond from each of the fluorine atoms to the central xenon. This gives us 4 bonds and uses 8 electrons. Each fluorine atom needs to complete its octet. The bond accounts for 2 electrons, so we need 6 more electrons (3 pairs) for each. Therefore, we add 3 separate pairs to each of the fluorine atoms. Six electrons per fluorine times 4 fluorine atoms accounts for 24 electrons. Our Lewis structure now contains 8 + 24 = 32 electrons. The number of available electrons (A) is 36, so we still need to add 36 - 32 = 4 electrons. These 4 electrons will give us 2 pairs. The xenon atom will get these pairs and become an exception to the octet rule. The actual placement of the pairs is not important as long as it is obvious that they are with the central atoms and not one of the fluorine atoms. The final Lewis structure is ... 

The N - A = S rule can be used to help draw the Lewis structure of a molecule. 

You can use the procedure outlined below to draw the Lewis structures for molecules and ions that have a central atom, with other atoms around it. The Sample Problems and additional text that follow show how to apply these steps for several molecules and polyatomic ions that obey the octet rule. Afterwards, use Practice Problems 9 to 13 to practice drawing Lewis structures. 

Drawing Lewis structures to assign oxidation numbers can be a very time-consuming process for large molecules or large polyatomic ions. Instead, the results from Lewis structures have been summarized to produce a more convenient set of rules, which can be applied more quickly. Table 10.1 summarizes the rules used to assign oxidation numbers. You may have discovered some of these rules for yourself in the ThoughtLab you just completed. 

For a given formula, it is possible to have a number of reasonable Lewis structures where the atoms have different connectivities, which means that different atoms are bonded to each other. Compounds with the same formula but different connectivities are known as isomers. Hydrogen atoms in benzene can be substituted by different atoms such as the halogens. Draw Lewis structures that obey the octet rule but present different arrangements of atoms for the compound dichlorobenzene, QH4C12. 

Draw a single bond (one pair of electron dots or a line) between each pair of connected atoms. Place the remaining electrons around the atoms as unshared pairs. If every atom has an octet of electrons except H, He, Li, and Be, which are atoms with two electrons, the Lewis structure is complete. Shared electrons count towards both atoms. If there are too few electron pairs to do this, draw multiple bonds (two or three pairs of electron dots between the atoms) until an octet is around each atom (except H atoms with two). If there are two many electron pairs to complete the octets with single bonds then the octet rule Is broken for this compound. 

In drawing Lewis structures for covalently bonded molecules, the octet rule is used as a guide (remember that for hydrogen the octet is changed to a duet). Shared electrons count toward the electron total for both atoms in the bond. For example, the Lewis structure for SiH4 looks like this ... 

Lewis structures can be used to draw the structures of covalent compounds. You should learn the rules for drawing these structures. 

For many simple compounds having no more than one double bond, the modern picture may be quite adequately represented by the Lewis structures (although the Lewis rules are noncommittal about the shapes of molecules). For compounds such as butadiene, benzene, and nitrous oxide, where there is extensive delocalization of electron density, the Lewis structures are not as suitable as the x-electron structures or, better still, as the streamer structures. Both of the latter type, however, are more difficult to draw and, for more complex molecules, more difficult to visualize they become extremely unwieldy when one attempts to use them to represent the progress of a chemical reaction. 

Can you propose a general rule for the numbers of hydrogen atoms in stable hydrocarbons Draw complete Lewis structures, including lone pairs, for the following compounds. 

When writing the Lewis structure for a molecule, first draw single bonds between all bonded atoms, and then satisfy the octet rule for all the atoms. If electrons remain after the octet rule has been satisfied, place them on the elements having available d orbitals (elements in the third period or beyond). 

Draw a Lewis structure that obeys the octet rule for each of the following molecules and ions. In each case the first atom listed is the central atom. 

Draw Lewis structures that obey the octet rule for the fol-... 

Lewis structures are electron dot representations for molecules. There are three general rules for drawing Lewis structures. 

Do you always follow the octet rule when drawing a Lewis structure Explain. 

The formulas of the chemical compounds are no accident. There is an NaCl, but no NaCl2 there is a Cap2, but no CaF. On the other hand, certain pairs of elements form two, or even more, different compounds, e.g. C]u20, CuO N2O, NO, NO2. In the case of ionic compounds the relative number of positive and negative ions in a formula is governed simply by the rule of electrical neutrality. In covalent compounds, or within polyatomic ions (like NO ), structures are formed by covalent bonds (i.e., electron sharing). A hierarchy of covalent bonding theories exists, of which the simplest, the drawing of Lewis structures, is emphasized in this and in most elementary texts. 

Our drawing of the Lewis structure for ozone (O3) satisfied the octet rule for the central atom because we placed a double bond between it and one of the two end O atoms. In fact, we can put the double bond at either end of the molecule, as shown by these two equivalent Lewis structures ... 

A rule for drawing plausible Lewis structures is that the central atom is invariably less electronegative than the surrounding atoms. Explain why this is so. 

Drawing Lewis Structures of Covalently Bonded Compounds That Are Exceptions to the Octet Rule... 

Describe the three exceptions to the octet rule, draw Lewis structures for them, and use formal charges to select the most... 

These species do not obey the octet rule. Draw a Lewis structure for each, and state the type of octet-rule exception ... 

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