Group 2 elements physical properties

Most hafnium compounds have been of slight commercial interest aside from intermediates in the production of hafnium metal. However, hafnium oxide, hafnium carbide, and hafnium nitride are quite refractory and have received considerable study as the most refractory compounds of the Group 4 (IVB) elements. Physical properties of some of the hafnium compounds are shown in Table 4. 

Compared with the lanthanides or the transition metals, the actinide elements introduce a striking array of novel chemical features, displayed most clearly in the chemistry of uranium. There is the variety of oxidation state, and to some extent the chemical diversity, typical of transition metals in the same periodic group, but physical properties which show that the valence electrons occupy /-orbitals in the manner of the lanthanides. This raises the question of the nature of the chemical bond in the compounds of these elements. The configuration of the uranium atom in the gas phase is f3ds2, so it is natural to ask whether there are special characteristics of the bonding that reflect the presence of both/and d valence orbitals. 

Within a periodic group the physical properties vary more predictably, especially if the elements are in the same physical state. For example, the melting points of argon and xenon are 189.2°C and 111.9°C, respectively. We can estimate the melting point of the intermediate element krypton by taking the average of these two values as follows ... 

These elements form two groups, often called the alkali (Group I) and alkaline earth (Group II) metals. Some of the physical properties usually associated with metals—hardness, high m.p. and b.p.—are noticeably lacking in these metals, but they all have a metallic appearance and are good electrical conductors. Table 6.1 gives some of the physical properties. 

All Group VI elements form a hydride HjX. With the notable exception of water, they are all poisonous gases with very unpleasant smells. Table 10.2 gives some of their important physical properties. 

Pure Elements. AH of the hehum-group elements are colorless, odorless, and tasteless gases at ambient temperature and atmospheric pressure. Chemically, they are nearly inert. A few stable chemical compounds are formed by radon, xenon, and krypton, but none has been reported for neon and belium (see Helium GROUP, compounds). The hehum-group elements are monoatomic and are considered to have perfect spherical symmetry. Because of the theoretical interest generated by this atomic simplicity, the physical properties of ah. the hehum-group elements except radon have been weU studied. 

Some of the physical properties of the hehum-group elements are summarized in Table 3. The values are those for the naturally occurring isotopic... 

Table 3. Physical Properties of the Helium-Group Elements...

Radon is the heaviest of the hehum-group elements and the heaviest of the normal gaseous elements. It is strongly radioactive. The most common isotope, Rn, has a half-life of 3.825 days (49). Radon s scarcity and radioactivity have severely limited the examination of its physical properties, and the values given ki Table 3 are much more uncertain than are the values Hsted for the other elements. 

Mixtures. A number of mixtures of the hehum-group elements have been studied and their physical properties are found to show Httle deviation from ideal solution models. Data for mixtures of the hehum-group elements with each other and with other low molecular weight materials are available (68). A similar collection of gas—soHd data is also available (69). 

Nickel occurs in the first transition row in Group 10 (VIIIB) of the Periodic Table. Some physical properties are given in Table 1 (1 4). Nickel is a high melting point element having a ductile crystal stmcture. Its chemical properties allow it to be combined with other elements to form many alloys. 

Rubidium [7440-17-7] Rb, is an alkali metal, ie, ia Group 1 (lA) of the Periodic Table. Its chemical and physical properties generally He between those of potassium (qv) and cesium (see Cesiumand cesium compounds Potassium compounds). Rubidium is the sixteenth most prevalent element ia the earth s cmst (1). Despite its abundance, it is usually widely dispersed and not found as a principal constituent ia any mineral. Rather it is usually associated with cesium. Most mbidium is obtained from lepidoHte [1317-64-2] an ore containing 2—4% mbidium oxide [18088-11-4]. LepidoHte is found ia Zimbabwe and at Bernic Lake, Canada. 

Barium is a member of the aLkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely aUied series in which the chemical and physical properties of the elements and thek compounds vary systematically with increa sing size, the ionic and electropositive nature being greatest for barium (see Calcium AND CALCIUM ALLOYS Calcium compounds Strontium and STRONTIUM compounds). As size increases, hydration tendencies of the crystalline salts increase solubiUties of sulfates, nitrates, chlorides, etc, decrease (except duorides) solubiUties of haUdes in ethanol decrease thermal stabiUties of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

These, though more difficult to describe quantitatively than the trends in atomic and physical properties described in the preceding subsection, also become apparent when the elements are compared in each group and along each period. Such trends will be discussed in detail in later chapters and it is only necessary here to enumerate briefly the various types of behaviour that frequently recur. 

The Group 1 elements are soft, low-melting metals which crystallize with bee lattices. All are silvery-white except caesium which is golden yellow "- in fact, caesium is one of only three metallic elements which are intensely coloured, the other two being copper and gold (see also pp. 112, 1177, 1232). Lithium is harder than sodium but softer than lead. Atomic properties are summarized in Table 4.1 and general physical properties are in Table 4.2. Further physical properties of the alkali metals, together with a review of the chemical properties and industrial applications of the metals in the molten state are in ref. 11. 

Chemical reactivity and group trends Table 10.2 Some physical properties of Group 14 elements... 

Arsenic, Antimony and Bismuth Table 13.4 Some physical properties of Group 15 elements... 

All the elements in a main group have in common a characteristic valence electron configuration. The electron configuration controls the valence of the element (the number of bonds that it can form) and affects its chemical and physical properties. Five atomic properties are principally responsible for the characteristic properties of each element atomic radius, ionization energy, electron affinity, electronegativity, and polarizability. All five properties are related to trends in the effective nuclear charge experienced by the valence electrons and their distance from the nucleus. 

Explain why lithium differs from the other Group 1 elements in its chemical and physical properties. Give two examples to support your explanation. 

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