Symbol Lewis

The octet rule doesn t always work, but for the representative elements, it works a majority of the time. 

as in most cases, hydrogen is an exception. Hydrogen achieves stability with a pair instead of an octet. 

In Sections 9-3 and 9-4, we will show you two types of chemical bonds ionic and covalent. It is important to be able to represent compounds in terms of the atoms and valence electrons that make up the chemical species (compounds or polyatomic ions). One of the best ways is to use Lewis symbols and structures. 

For the representative elements, the valence electrons are all electrons in the outer s and p orbitals of an atom. A quick way of determining the number of valence electrons is to locate the element on the periodic table. There are eight columns of representative elements. The first column, headed by H and Li, has one valence electron, the second column has two, skip the transition elements, the next column, headed by B and Al, has three. This continues to the last (eighth) column where there are eight valence electrons. The only exception to this procedure is helium, which only has two valence electrons. 

In Chapter 2, we saw molecular and empirical formulas. Recall that the molecular formula indicates the kind and actual number of atoms present. The empirical formula simply shows the kind of atoms present and their lowest whole number ratio. In this chapter, structural formulas are important. The Lewis formula of a compound is an example of a structural formula. A structural formula shows the number and type of atoms present, as well as the bonding pattern. The bonding pattern shows which atoms bond to each other. It usually 

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As will become apparent as this chapter progresses, many of our basic ideas on the chemical bond were proposed by Ci. N. Lewis, one of the greatest of all chemists, in the early years of the twentieth century. Lewis devised a simple way to keep track of valence electrons when atoms form ionic bonds. He represented each valence electron as a dot and arranged the dots around the symbol of the element. A single dot represents an electron alone in an orbital a pair of dots represents two paired electrons sharing an orbital. Examples of the Lewis symbols of atoms are... 

The Lewis symbol for nitrogen, for example, represents the valence electron configuration 2s22pA.12p>112p 1 (see 1), with two electrons paired in a 2s-orbital and three unpaired electrons in different 2p-orbitals. The Lewis symbol is a visual summary of the valence-shell electron configuration of an atom and allows us to see what happens to the electrons when an ion forms. 

We can extend the Lewis symbols introduced in Section 2.2 to describe covalent bonding by using a line (—) to represent a shared pair of electrons. For example, the hydrogen molecule formed when two H- atoms share an electron pair (H=H) is represented by the symbol H—H. A fluorine atom has seven valence electrons and needs one more to complete its octet. It can achieve an octet by accepting a share in an electron supplied by another atom, such as another fluorine atom ... 

Let s construct the Lewis structure for the simplest organic molecule, the hydrocarbon methane, CH4. First, we count the valence electrons available from all the atoms in the molecule. For methane, the Lewis symbols of the atoms are... 

A biradical is a molecule with two unpaired electrons. The unpaired electrons are usually on different atoms, as depicted in (20). In that biradical, one unpaired electron is on one carbon atom of the chain and the second is on another carbon atom several bonds away. In some cases, though, both electrons are on the same atom. One of the most important examples is the oxygen atom itself. Its electron configuration is He]2s22/ x.22py12pzl and its Lewis symbol is -O. The O atom has two unpaired electrons, and so it can be regarded as a special type of biradical. 

The oxygen atom, with valence electron configuration 2s12px12pv 12p J, has two electrons with unpaired spins (its Lewis symbol is -O-, which we abbreviate to -0-). Two radicals are also produced when the oxygen atom attacks a hydrogen molecule ... 

Lewis symbol (for atoms and ions) The chemical symbol of an element, with a dot for each valence electron. 

Lewis, G. N., 60, 64, 398 Lewis acid, 398, 473, 671 Lewis base, 398, 473 Lewis structure, 65 writing, 67 Lewis symbol, 60 Lewis theory, limitations of, 115... 

Lewis recognized that certain molecules such a PCI5 and SF6 are exceptions to the octet rule because their Lewis structures indicate that the central atom has more than eight electrons in its valence shell 10 for the P atom in PCI5 and the S atom in SF4, and 12 for the S atom in SFg (Figure 1.17). Such molecules are called hypervalent because the valence of the central atom is greater than its principal valence. To write a Lewis structure for such molecules, the Lewis symbol for the hypervalent atom must be modified to show the correct number of unpaired electrons. For the molecules in Figure 1.17 we would need to write the Lewis symbols as follows ... 

IB Sn is in Family 4A, and thus has 4 electrons and 4 dots in its Lewis symbol. Br is in Family 7 A with 7 valence electrons. Adding an electron produces an ion with 8 valence electrons. T1 is in Family 3A with 3 valence electrons. Removing an electron produces a cation with 2 valence electrons. 

This representation is also known as the Lewis symbol representation. In this representation valence electrons are shown as dots around the symbol of the element. 

Bond structure can also be represented by lines. Each electron pair is shown by a line. In other words two electrons are shown by a line So the line representation of the fluorine molecule is IF—FI. The line between the two fluorine atoms represents the bond. Sometimes both the Lewis symbol and line representation can be used in the same molecule. For example, the F2 molecule can also be represented as F— F ... 

Lewis structure The structural formula drawn with Lewis symbols that shows the valence electrons using dots. 

How many electrons should the Lewis symbols of each of the following elements indicate ... 

Using Lewis symbols, write a balanced chemical equation showing the formation of lithium fluoride, LiF, from isolated lithium and fluorine atoms. 

The Lewis electron-dot symbol is a way of representing the element and its valence electrons. The chemical symbol is written, which represents the atom s nucleus and all inner-shell electrons. The valence, or outer-shell, electrons are represented as dots surrounding the atom s symbol. Take the valence electrons, distribute them as dots one at a time around the four sides of the symbol and then pair them up until all the valence electrons are distributed Figure 11.1 shows the Lewis symbol for several different elements. 

The Lewis symbols will be used in the discussion of bonding, especially covalent bonding, and will form the basis of the discussion of molecular geometry. 

To work out the formula of an ionic compound using Lewis symbols, we first represent the cation by removing the dots from the symbol for the metal atom. Then we represent the anion by transferring those dots to the Lewis symbol for the nonmetal atom to complete its valence shell. We may need to adjust the numbers of atoms of each kind so that all the dots removed from the metal atom symbols are accommodated by the nonmetal atom symbols. Finally, we write the charge of each ion as a superscript in the normal way. A simple example is the formula of potassium chloride ... 

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