Period 3 elements bond types

Finally, a special type of primary bond known as a metallic bond is found in an assembly of homonuclear atoms, such as copper or sodium. Here the bonding electrons become decentralized and are shared by the core of positive nuclei. Metallic bonds occur when elements of low electronegativity (usually found in the lower left region of the periodic table) bond with each other to form a class of materials we call metals. Metals tend to have common characteristics such as ductility, luster, and high thermal and electrical conductivity. All of these characteristics can to some degree be accounted for by the nature of the metallic bond. The model of a metallic bond, first proposed by Lorentz, consists of an assembly of positively charged ion cores surrounded by free electrons or an electron gas. We will see later on, when we... 

Electron sharing results in the type of bonding that usually occurs between two nonmetals (that is, two elements that are both on the far right of the periodic table). This type of bonding is termed covalent bonding. As we ve seen, the valence electrons are those electrons in the outermost shell of an atom. For instance, carbon, in the fourth position on the second row, has six total electrons (being the sixth element listed on the periodic table), but only four of these are valence electrons, that is, electrons in the outer shell. Covalent means that electrons are being shared cooperatively and act as valence electrons for both the elements in the bond. 

In a covalent bond both atoms attract electrons and share electrons between them. A metallic bond is favored between metals. In a metallic bond, atoms lose electrons to a matrix of free electrons surrounding them. Many bonds have some characteristics of more than one of the above basic bond types. Electronegativity and the location of metallic and nonmetallic elements on the periodic table are described in Skill 1.1c and 12.11. 

A metal and a nonmetal—elements from opposite sides of the periodic table— have a relatively large AEN and typically interact by electron transfer to form an ionic compound. Two nonmetals—elements from the same side of the table— have a small AEN and interact by electron sharing to form a covalent compound. When we combine the nonmetal chlorine with each of the other elements in Period 3, starting with sodium, we should observe a steady decrease in AEN and a gradation in bond type from ionic through polar covalent to nonpolar covalent. 

Figure 9.23 Properties of the Period 3 chlorides. Samples of the compounds formed from each of the Period 3 elements with chlorine are shown in periodic table sequence in the photo. Note the trend in properties displayed in the bar graphs as AEN decreases, both melting point and electrical conductivity (at the melting point) decrease. These trends are consistent with a change in bond type from ionic through polar covalent to nonpolar covalent.

Only a few examples of o-bonded metal-carbon porphyrins are now known, but it is theoretically possible to prepare and characterize representative complexes with almost all elements in the periodic table. These types of syntheses could lead to the related synthesis of numerous novel bimetallic or dimeric derivatives. 

Semiconductors can be divided into two classes, elemental semiconductors, which contain only one type of atom, and compound semiconductors, which contain two or more elements. The elemental semiconductors all come from group 4A. As we move down the periodic table, bond distances increase, which decreases orbital overlap. This decrease in overlap reduces the energy difference between the top of the valence band and the bottom of the conduction band. As a result, the band gap decreases on going from diamond (5.5 eV, an insulator) to silicon (1.11 eV) to germanium (0.67 eV) to gray tin (0.08 eV). In the heaviest group 4A element, lead, the band gap collapses altogether. As a result, lead has the structure and properties of a metal. 

Figure 9.3 Gradations in bond type among Period 3 (black type)and Group 4A (red type elements.

Anions of the type (MO ) , such as sulfate, S04, and nitrate, NO ", are called OXYANiONS. Their structures are of particular interest because they reveal the role played by tt bonding as influenced by the size of the central atom. The oxyanions of the second period elements, B, C, and N,... 

The augmented MM2 force field implemented in CAChe covers all elements of the periodic table up to Lr. It is based on Allinger s MM2, but has been extended for the elements and bond types (e.g, weak, ionic, coordinate) not included in the original program. All mechanics parameters are adjustable, thus enabling the user to calibrate the results against experimental data (e.g., X-ray structures) on the particular family of compounds of interest. It can... 

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