Hydrogen A Unique Element

Group 16 The Oxygen Family 22-5 Group 15 The Nitrogen Family 22-6 Hydrogen A Unique Element... 

Hydrogen is a unique element in many respects. Its scarcity on Earth is partially due to the low density of hydrogen gas. The low density permits hydrogen molecules to escape Earth s gravitational pull and drift into space. 

Hydrogen is a unique element in the sense that its isotopes differ in their physical and chemical properties. At one time this difference prompted some scientists to consider... 

Although we do not really understand completely how petroleum deposits were formed, they most likely came from the remains of marine organisms living over 500 million years ago. Petroleum is composed of hydrocarbon compounds (which contain only carbon and hydrogen). Carbon is a unique element in that it can produce chains of atoms in a molecule of different lengths. Table 4.4 gives the names and formulas of some simple hydrocarbons. Natural gas is associated with petroleum deposits and consists mainly of methane with some ethane, propane, and butane mixed in. 

Most elements are classified as metals (see Figure 11.1). Metals are found on the left side of the stair-step line, while the nonmetals are located toward the upper right of the table. Note that hydrogen does not fit into the division of metals and non-metals. It displays nonmetallic properties under normal conditions, even though it has only one outermost electron like the alkali metals. Hydrogen is considered to be a unique element. 

In the case of boron, the hydroxo ligands in B(OH) i bear a negative partial charge. However, boric acid does not condense because the partial charge on the cation is too small. The monomeric form B(OH)3 is stable in solution. The solid phase, obtained after drying, is made of monomeric units connected by hydrogen bonds [15,21]. Boron appears to be a unique element in the respeet that the coordination 3 in boric acid is stabilized by the strong tt character of the B-OH bonds. After alkalinization, borates.are in tetrahedral coordination and are able to form polyanions with boric acid (see Chapter 4). 

Figure 5.13 shows the way in which the molecules are visualised, their chemical symbol, and the names of the first three members of the series. The carbon atom has four bonds that can join with either one or more carbon atoms (a unique-property) or with atoms of other elements, such as hydrogen. Hydrogen has only one bond, and can therefore join with only one other atom. 

Each element is represented by a unique one- or two-letter symbol. For example, the symbol for hydrogen is H, oxygen s symbol is O, and nitrogen s symbol is N. When two or more elements have names that begin with the same English letter, all but one of the elemental symbols has a second letter. The second letter is always lower case. For example, carbon is C, chlorine is Cl, cobalt is Co, and chromium is Cr. Chemists understand that the symbol for an element represents more than one or two letters. Instead, a chemist sees the symbol Ni and immediately thinks of nickel atoms. 

Hydrogen bound covalently to nitrogen, oxygen or fluorine may bond with another atom of one of these elements by a unique linkage known as the hydrogen bond . Since the hydrogen nucleus cannot control more than two electrons this is not a covalent bond but a powerful dipole-dipole interaction, traditionally indicated by dotted lines. It occurs in water, hydrofluoric acid, undissociated ammonium hydroxide and many hydrates, e.g. ... 

First and foremost among these was the atomic theory. Throughout the century, chemists were divided about the validity of so-called physical atomism, namely, that there exists a unique indivisible particle specific to each chemical element and characterized by an atomic weight that some chemists sought to prove was a multiple of the standard weight of hydrogen (or its subweight). 

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