Metallic elements electronegativity

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

Two types of chemical bonds, ionic and covalent, are found in chemical compounds. An ionic bond results from the transfer of valence electrons from the atom of an electropositive element (M) to the atom(s) of an electronegative element (X). It is due to coulombic (electrostatic) attraction between the oppositely charged ions, M (cation) and X (anion). Such ionic bonds are typical of the stable salts formed by combination of the metallic elements (Na, K, Li, Mg, etc.) with the nonmetallic elements (F, Cl, Br, etc.). As an example, the formation of the magnesium chloride molecule from its elemental atoms is shown by the following sequence ... 

The electronegativity of C is 2.54, as compared with 1.92 for Si. Carbon is strictly nonmetallic whereas Si is essentially a non-metallic element with some metalloid properties. 

Electronegativity measures the ability of an atom to attract electrons in a chemical bond. The most metallic elements have the lowest electronegativity. The most nonmetallic have the highest electronegativity. 

Polar Covalent Nonmetals and non-metals Electrons are not shared evenly. Electrons spend more time with more electronegative element. Electronegativity differences are 0.5 to 1.7. Yes Weaker. Have low melting points. Ex. water, ice... 

An atom that has a small electronegativity is said to be electropositive. As the diagram shows, the metallic elements are generally electropositive. The position of hydrogen in this regard is worth noting although physically a nonmetal, much of its chemisry is metal-like. 

Figure 3 The standard reduction potential (E°) ofthe most common cation of each metallic element versus its Pauling electronegativity. (Ref. 3. Reproduced by permission of University Science Books)...

On the other hand, in Hume-Rothery s classification of the elements boron is one of two placed in its own box as neither metal, intermediate element, or nonmetal (12). Indeed, there are properties of boron and features of boron chemistry that are similar to those of transition metals. The electronegativity of boron is less than that of hydrogen as is the electronegativity of most transition metals. This property is also common to other nonmetals past the first row (e.g., silicon). There is, however, one crucial difference between boron and other elements such as silicon. Because it lies to the left of carbon, boron has fewer valence electrons than valence orbitals. Elements with this electronic feature are usually found to exhibit metallic bonding in the elemental state but... 

The unfavorable electronegativity issue refers specifically to the early transition metal elements, especially the group III (Sc, Y, actinides, and lanthinides) elements. The more electropositive elements form an equilibrium with Grignard reagents, giving the other alternative reactions a chance to occur, resulting in poor yields of the desired product. 

The chemical elements provide examples of three of the four classes of crystalline solids described in this section. Only ionic solids are excluded, because a single element cannot have the two types of atoms of different electronegativities needed to form an ionic material. We have already discussed some of the structures formed by metallic elements, which are sufficiently electropositive that their atoms readily give up electrons to form the electron sea of metallic bonding. The nonmetallic elements are more complex in their structures, reflecting a competition between intermolecular and intramolecular bonding and producing molecular or covalent solids with varied properties. 

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