Silicon aluminum-phosphorus bonds

Different elective affinity of elements as compared to carbon. Electropositive elements (Si, B, AI, P) have a considerably larger affinity to electronegative elements than carbon. In other words, silicon, boron, aluminum, phosphorus and other elements form weaker bonds with electropositive elements (H, Si, B, Al, As, Sb, Bi, etc.), and stronger bonds with electronegative elements (O, N, Cl, Br, F, etc.) than carbon. 

Unlike the interstitial nitrides, the covalent nitrides are not metallic compounds. The differences in electronegativity and atomic size between the nitrogen and the other element are small and their electronic bonding is essentially covalent. In this respect, they are similar to the covalent carbides. They include the nitrides of Group mb (B, Al, Ga, In, Tl) and those of silicon and phosphorus. Of these, only three are considered refractory boron nitride, silicon nitride, and aluminum nitride. These are reviewed in Chs. 12 and 13. 

Across a period. The decrease in metallic behavior across a period is consistent with a decrease in size, an increase in IE, and a more favorable (more negative) EA. Consider Period 3 elements at the left tend to form cations, and those at the right tend to form anions. Sodium and magnesium are metals that occur as Na and Mg - in seawater, minerals, and organisms. Aluminum is a metallic element and occurs as Al + in some compounds, but it bonds covalently in most others. Silicon (Si) is a shiny metalloid that does not occur as a monatomic ion. Phosphorus is a white, waxy nonmetal that occurs rarely as P, whereas crumbly, yellow sulfur forms S in many compounds, and gaseous, yeUow-green chlorine occurs in nature almost always as Cl . 

X-ray diffraction analysis of this cement system gives only those peaks attributable to wollastonite. It is suggested that an acid-crystal surface interaction occurs, reducing the apparent wollastonite surface area and freeing the bonding constituents for matrix development. Microprobe analysis shows that the matrix binding wollastonite grains contains phosphorus, calcium, silicon, and some aluminum and zinc. 

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