Covalent compounds Lewis structures

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... 

What Do We Need to Know Already It would be a good idea to review the information on periodic trends in Sections 1.15-1.22 and 14.1-14.2. Because the nonmetals form molecular compounds, it would also be helpful to review Lewis structures, electronegativity, and covalent bonding in Chapters 2 and 3. The bulk properties of nonmetallic materials are affected by intermolecular forces (Sections 5.1-5.5). 

Ca— 0 is improperly written as a covalent Lewis structure, although CaO is an ionic compound. In addition, there are only two electrons around the Ca atom. [Ca]2+[ 0 ]2" is a more plausible Lewis structure for CaO. 

Creating the Lewis structures of molecules is a method for determining the sequence of bonding within a molecule and its three-dimensional shape. This works best for covalently bonded molecules, but can also work for ionic compounds. For example, this method can be used to explain why the sequence of bonding in water is H-O-H, rather than H-H-O, and why it has a bent structure, rather than linear. 

A Lewis structure can show the bonding pattern in a covalent compound. In Lewis formulas, we show the valence electrons that are not involved in bonding as dots surrounding the element symbols. The valence electrons involved in bonding are present as dashes. There are several ways of deriving the Lewis structure, but here is one that works well for most compounds that obey the octet rule. 

This Lewis structure shows methane, the simplest organic compound. The carbon atom has four valence electrons, and it obtains four more electrons by forming four covalent bonds with the four hydrogen atoms. 

In this section, you have used Lewis structures to represent bonding in ionic and covalent compounds, and have applied the quantum mechanical theory of the atom to enhance your understanding of bonding. All chemical bonds—whether their predominant character is ionic, covalent, or between the two—result from the atomic structure and properties of the bonding atoms. In the next section, you will learn how the positions of atoms in a compound, and the arrangement of the bonding and lone pairs of electrons, produce molecules with characteristic shapes. These shapes, and the forces that arise from them, are intimately linked to the physical properties of substances, as you will see in the final section of the chapter. 

Almost simultaneous with the publication of Kossel s paper there appeared a rival electronic theory. The American chemist Lewis introduced the idea of the covalent electron-pair bond. Like Kossel, he was impressed by the apparent stability of the noble gas configuration. He was also impressed by the fact that, apart from many compounds of the transition elements, most compounds when rendered as molecules have even numbers of electrons, suggesting that electrons are usually found in pairs. Lewis devised the familiar representations of molecules and polyatomic ions (Lewis structures, or Lewis diagrams) in which electrons are shown as dots (or as noughts and crosses) to show how atoms can attain noble gas configurations by the sharing of electrons in pairs, as opposed to complete transfer as in Kossel s theory. It was soon apparent from the earliest X-ray studies that Kossel s theory was more appropriate... 

Explain whether the bonds in these compounds would be ionic or covalent and show Lewis structures for them ... 

In order to fully appreciate and understand molecular structure, you will need to be able to construct representations of various molecules. One of the easiest ways to do this is using Lewis structures. The procedure is a bit more complicated than for ionic compounds because of the increasing complexity of covalent compounds. The basic procedure for constructing Lewis diagrams of molecules consists of 4 steps ... 

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

Use Lewis structures to show the simplest way in which each pair of elements forms a covalent compound, according to the octet rule. 

You have used Lewis structures to demonstrate how ionic and covalent bonds form between atoms. When given two elements, you determined how many atoms of each element bond together to form a compound, according to the octet rule. For example, you used the periodic table and your understanding of the octet rule to determine how calcium and bromine bond to form an ionic compound. Using a Lewis structure, you determined that calcium and bromine form a compound that contains two bromine atoms for every calcium atom, as shown in Figure 3.39. 

You have seen how Lewis structures can help you draw models of ionic, covalent, and polar covalent compounds. When you draw a Lewis structure, you can count how many electrons are needed by each atom to achieve a stable octet. Thus, you can find out the ratio in which the atoms combine. Once you know the ratio of the atoms, you can write the chemical formula of the compound. Drawing Lewis structures can become overwhelming, however, when you are dealing with large molecules. Is there a faster and easier method for writing chemical formulas ... 

You can use valences to write chemical formulas. This method is faster than using Lewis structures to determine chemical formulas. As well, you can use this method for both ionic and covalent compounds. In order to write a chemical formula using valences, you need to know which elements (or polyatomic ions) are in the compound, and their valences. You also need to know how to use the zero sum rule For neutral chemical formulas containing ions, the sum of positive valences plus negative valences of the atoms in a compound must equal zero. 

Draw a Lewis structure to represent each covalent compound. 

Draw Lewis structures to represent the following covalent compounds. 

Describe a weakness of using Lewis structures to model covalent compounds. 

Use the following terms to create a concept map valence electrons, nonpolar, covalent compounds, polar, dipoles, and Lewis structures. 

Lewis Structure Covalent Compound with Single Bonds... 

The polyatomic ions you learned about in Chapter 8 are related to covalent compounds. Although the unit acts as an ion, the atoms within the ion itself are covalently bonded. The structures of these ions can also be represented by Lewis structures. 

Q.4. Predict the Lewis structure of the simple compound for both ionic and covalent structures, comment on a non-octet configuration and estimate the formal charge on each atom, where appropriate. 

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