Main-group elements Lewis symbol

Lewis symbols are named after G. N. Lewis (1875-1946), an American chemist who contributed greatly to our understanding of chemical bonding. Lewis symbols, or electron-dot symbols, show the number of valence electrons possessed by an element. They are used only for the main-group elements. Here is how Lewis symbols are written ... 

It s easy to write the Lewis symbol for any main-group element ... 

The electron configurations and Lewis symbols for the main-group elements of periods 2 and 3 are shown in T TABLE 8.1. Notice that the number of valence electrons in any representative element is the same as the element s group number. For example, the Lewis symbols for oxygen and sulfur, members of group 6A, both show six dots. 

Lewis symbols for the main group elements are shown in Figure 7.6. 

As we discussed in Chapter 9, valence electrons are those in the outermost principal shell. Since valence electrons are most important in bonding, Lewis theory focuses on these. In Lewis theory, the valence electrons of main-group elements are represented as dots siuToimding the symbol of the element. The result is called a Lewis stmcture, or dot structure. For example, the electron configuration of O is ... 

The Lewis structure of any element is the symbol for the element with the valence electrons represented as dots drawn aroxmd the element. The number of valence electrons is equal to the group number of the element (for main-group elements). 

Given a metallic and a nonmetalUc main-group element, use Lewis symbols to represent the transfer of electrons to form ions of noble-gas configurations. (EXAMPLE 9.1)... 

Writing electron configurations of ions Given an ion, write the electron configuration. For an ion of a main-group element, give the Lewis symbol. (EXAMPLES 9.2,93)... 

Write the Lewis (electron-dot) symbol for an atom of any main group element. 

Another way to show valence electrons uses Lewis symbols, which are also called electron-dot symbols. The symbol of the element is surrounded by the number of dots that matches the number of valence electrons. Dot symbols for the main group elements in Period 3 are given in Table 11.1. Paired electrons, those that occupy the same orbital, are usually placed on the same side of the symbol, and single occupants of one orbital are by themselves. This is not a fixed rule exceptions are common if other positions better serve a particular purpose. 

COAL 13 Using n for the highest occupied energy level, write the configuration of the valence electrons of any main group element. COAL 14 Write the Lewis (electron-dot) symbol for an atom of any main group element. 

Figure 8.1 Lewis dot symbols of the main group elements.

When atoms interact to form compounds, it is their valence electrons that actually interact. Therefore, it is helpful to have a method for depicting the valence electrons of the atoms involved. This can be done using Lewis dot symbols. A Lewis dot symbol consists of the element s symbol surrounded by dots, where each dot represents a valence electron. For the main group elements, the number of dots in the Lewis dot symbol is the same as the group number, as shown in Figure 8.1. (Because they have incompletely filled inner shells, transition metals typically are not represented with Lewis dot symbols.)... 

A Lewis dot symbol depicts an atom or an atomic ion of a main group element with dots (representing the valence electrons) arranged around the element s symbol. Main group atoms lose or gain one or more electrons to become isoelectronic with noble gases. 

Electron spin had not yet been proposed when Lewis framed his theory, and so he did not show that two of the valence electrons (3s ) are paired and two (3p ) are unpaired. We will write Lewis symbols in the way Lewis did. We will place single dots on the sides of the symbol, up to a maximum of four. Then we will pair up dots until we reach an octet. Lewis symbols are commonly written for main-group elements but much less often for transition elements. Lewis symbols for several main-group elements are written in Example 10-1. 

The position of the element in the periodic table determines the number of valence electrons in the Lewis symbol. For main-group elements, the number of valence electrons, and hence the number of dots appearing in a Lewis symbol, is equal to the group number for the s-block elements and to the group number minus 10 for the p-block elements. 

In Section 3-2, we learned that the formula unit of an ionic compound is the simplest electrically neutral collection of cations and anions from which the chemical formula of the compound can be established. The Lewis structure of sodium chloride (equation 10.1) represents its formula unit. For an ionic compound of a main-group element, (1) the Lewis symbol of the metal ion has no dots if all the valence electrons are lost, and (2) the ionic charges of both cations and anions are shown. These ideas are further illustrated through Example 10-2. 

The starting point for the Lewis structure is a notation for an atom and its valence electrons. The element symbol represents the core, that is, the nucleus and all the inner-shell electrons. The core carries a number of positive charges equal to the number of valence electrons. This positive charge is called the corechanie. Valence electrons are shown explicitly. For elements in the third and later rows of the periodic table, the d electrons in atoms of Main Groups III, IV, V, VI, and VII are counted as part of the core. Thus ... 

The Lewis electron-dot symbol of a main-group atom shows valence electrons as dots surrounding the element symbol. 

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