Main group elements noble gases

Figure 7.3 Periodic table with color-coding of main group elements, noble gases, transition metals, group 2B metals, lanthanides, and actinides.

The pattern of ion formation by main-group elements can be summarized by a single rule for atoms toward the left or right of the periodic table, atoms lose or gain electrons until they have the same number of electrons as the nearest noble gas atom. Thus, magnesium loses two electrons and becomes Mg2+, which has the same number of electrons as an atom of neon. Selenium gains two electrons and becomes Se2, which has the same number of electrons as krypton. We shall discover the origin of this rule in Section 2.3. 

Recall from Chapter 7 that elements in the same group (vertical column) of the periodic table have the same number of valence electrons, and because of this, they have similar properties. But elements in a period (horizontal row) have properties different from one another. This is because the number of valence electrons increases from one to eight as you move from left to right in any row of the periodic table except the first. As a result, the character of the elements changes. Figure 8.1 illustrates the main group elements and shows that each period begins with two or more metallic elements, which are followed by one or two metalloids. The metalloids are followed by nonmetallic elements, and every period ends with a noble gas. 

The pattern metal-metalloid-nonmetal-noble gas is typical for the main group elements in each period. Period 2 begins with a metal, lithium, and ends with a noble gas, neon. In between are the metal beryllium the metalloid boron and the nonmetals carbon, nitrogen, oxygen, and fluorine. Remember that the most active metals. Groups 1 and 2, are in the s region of the periodic table. The metalloids, nonmetals, and less active metals are in the p region of the periodic table. 

Write the ground state configuration of the following main-group elements and their ions. Identify the noble gas configuration of each ion. 

The previous examples have involved only main-group elements since they form monatomic ions with noble gas configurations in agreement with the octet rule. This predictable behavior lets you figure out formulas of ionic products if you know the electronic configurations of the reactants. 

Answer In reactions involving main-group elements, atoms tend to gain, lose, or share the necessary number of electrons needed to achieve an octet of electrons in their valence shells. It does not apply to transition metals, nor does it apply to hydrogen or lithium. Realize, an octet of electrons implies a noble gas configuration. ... 

The central idea of the ionic bonding model is the transfer of electrons from meted atoms to nonmetal atoms to form ions that come together in a solid ionic compound. For nearly every monatomic ion of a main-group element, the electron configuration has a filled outer level either two or eight electrons, the same number as in the nearest noble gas (octet rule). 

Octet rule For the remainder of the main-group elements, the octet rule dictates the number of valence electrons an atom wants. The eight electrons are directly related to the s p noble gas electronic configuration. With two electrons in the s orbital and sbt electrons in the p orbitals, the noble gas is full with eight electrons (hence the term octet rule). 

Look now at the next noble gas, neon (Ne). Its place in family 8A means that its valence shell has already eight electrons.Ne is electronically satisfied and will therefore not form covalent electron-pair bonds. The other atoms in the same period will form electron-pair bonds until they fill eight electrons around them— chemists use the term octet for the figure 8. Thus, the Octet Rule states that the connectivity of such an atom will be the number of electrons it lacks to reach an octet in its valence shell. The same applies to all other periods of main group elements the connectivity of the atoms in these periods will be equal to the number of electrons they lack to reach octet in their valence shells. 

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