Magnesium atomic properties

The special properties of ethers (polarity, lone pairs, but relatively unreactive) enhance the formation and use of many reagents. For example, Grignard reagents cannot form unless an ether is present, possibly to share its lone pairs of electrons with the magnesium atom. This sharing of electrons stabilizes the reagent and helps keep it in solution (Figure 14-4). 

The aggregation properties of chlorophyll, which are responsible for the formation of the "photosynthetic dimer" are due to the interaction of the central magnesium atom... 

This stmcture has a negative lattice charge for every magnesium atom that has replaced an aluminum atom, and the mineral has base exchange properties. Iron also replaces some of the aluminum atoms in the lattice. 

The side chains of the 20 different amino acids listed in Panel 1.1 (pp. 6-7) have very different chemical properties and are utilized for a wide variety of biological functions. However, their chemical versatility is not unlimited, and for some functions metal atoms are more suitable and more efficient. Electron-transfer reactions are an important example. Fortunately the side chains of histidine, cysteine, aspartic acid, and glutamic acid are excellent metal ligands, and a fairly large number of proteins have recruited metal atoms as intrinsic parts of their structures among the frequently used metals are iron, zinc, magnesium, and calcium. Several metallo proteins are discussed in detail in later chapters and it suffices here to mention briefly a few examples of iron and zinc proteins. 

Table 6-VI11 presents some properties of the elements we are considering. The first three, sodium, magnesium, and aluminum, are metallic. The melting points and boiling points are high and increase as we go from element to element. This trend reflects stronger and stronger bonding and it is paralleled by a decrease in the atomic volume.

The lobes of electron density outside the C-O vector thus offer cr-donor lone-pair character. Surprisingly, carbon monoxide does not form particularly stable complexes with BF3 or with main group metals such as potassium or magnesium. Yet transition-metal complexes with carbon monoxide are known by the thousand. In all cases, the CO ligands are bound to the metal through the carbon atom and the complexes are called carbonyls. Furthermore, the metals occur most usually in low formal oxidation states. Dewar, Chatt and Duncanson have described a bonding scheme for the metal - CO interaction that successfully accounts for the formation and properties of these transition-metal carbonyls. 

Some physical and chemical properties of the alkaline earth metals are shown in Table II. It can be seen that beryllium is significantly different from the elements below it in the periodic table in most respects. The fact that the density of beryllium is greater than that of magnesium is perhaps surprising, but can be understood by noting that magnesium is both a more massive and a larger atom. The density of beryllium is to be compared to that of iron (7.9 g cm-3), titanium (4.5 g cm-3), and aluminum (2.7 g cm-3). 

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