Non-metallic elements

As in the case of metals, non-metallic constituents such as halogens, nitrogen and sulphur can occur in polymers in amounts ranging from a few parts per million (eg. traces of chlorine catalyst remnants in polyolefins) up to tens of percent (eg. chlorine in PVC, nitrogen in polyamides). 

It is advisable when starting polymer analysis to determine the content of various non-metallic and metallic elements first. Initially, these tests could be qualitative, simply to indicate the presence or absence of the element. All that is required is that the test is of sufficient sensitivity such that elements of importance are not missed. If an element is found in these tests, it may be necessary to determine it quantitatively. The analytical methods used to determine elements should be sufficiently sensitive to determine about 10 ppm of an element in the polymer. That is, in a polymer, the method must detect a substance present at 0.01% and containing down to 10% of the element in question. 

This requirement is met for almost all the important elements by using optical emission spectroscopy and X-ray fluorescence spectrometry (XRFS). The latter is applicable to all elements with an atomic number 12. Using these two techniques, all metals and non-metals down to an atomic number of 15 (phosphorus) can be determined in polymers at the required concentrations [1 ]. 

Nitrogen can be determined by micro Kjeldahl digestion techniques. 

Commercial instrumentation available for the determination of halogens sulfur halogens and sulfur nitrogen nitrogen, carbon, and sulfur carbon, hydrogen, and nitrogen and total organic carbon (TOC) is the subject of this chapter. 

---

Essentially the same processes occur when chlorides (for example) of non-metallic elements dissolve in water. Thus, the enthalpy changes for hydration chloride can be represented ... 

This is an exothermic process, due largely to the large hydration enthalpy of the proton. However, unlike the metallic elements, non-metallic elements do not usually form hydrated cations when their compounds dissolve in water the process of hydrolysis occurs instead. The reason is probably to be found in the difference in ionisation energies. Compare boron and aluminium in Group III ... 

In this group the outer quantum level has a full s level and two electrons in the corresponding p level. As the size of the atom increases the ionisation energy changes (see Table 8.1) and these changes are reflected in the gradual change from a typical non-metallic element, carbon, to the weakly metallic element, lead. Hence the oxides of carbon and silicon are acidic whilst those of tin and lead are amphoteric. 

Nitrogen is unusual in forming so many oxides. The acidity of the Group V oxides falls from phosphorus, whose oxides are acidic, through arsenic and antimony whose oxides are amphoteric, to the basic oxide ofbismuth. This change is in accordance with the change from the non-metallic element, phosphorus, to the essentially metallic element, bismuth. The +5 oxides are found, in each case, to be more acidic than the corresponding + 3 oxides. 

These elements are generally unaffected by non-oxidising acids (behaviour expected for non-metallic elements) but they do react when heated with concentrated sulphuric and nitric acids, both powerful oxidising agents. Sulphur is oxidised to sulphur dioxide by hot concentrated sulphuric acid,... 

Sulphur is less reactive than oxygen but still quite a reactive element and when heated it combines directly with the non-metallic elements, oxygen, hydrogen, the halogens (except iodine), carbon and phosphorus, and also with many metals to give sulphides. Selenium and tellurium are less reactive than sulphur but when heated combine directly with many metals and non-metals. 

For the majority of metals, the evaporation coefficient is found to be unity, but, as mentioned before, the coefficient of many non-metallic elements with a complex vaporization mechanism such as... 

Fig. 2.29. Formation of surface compounds on Fe-15%Cr alloys by cosegregation of chromium and a non-metallic element [2.160]. (a) nitride, (b) carbide, (c) sulfide.

The Group 13 metals differ sharply from the non-metallic element boron both in their greater chemical reactivity at moderate temperatures and in their well-defined cationic chemistry for aqueous solutions. The absence of a range of... 

The analysis of non-metallic elements and anionic species may present a problem since many do not readily form suitable derivatives for fluorimetric... 

Thin layer and filter paper chromatography of metal complexes and some non-metal elements. R. L. Dutta, R. K. Ray and G. B. Kauffman, Coord. Chem. Rev., 1979, 28, 23-45 (93). 

The second part is a review of the materials deposited by CVD, i.e., metals, non-metallic elements, ceramics and semiconductors, and the reactions used in their deposition. 

This chapter is a review of the CVD of non-metallic elements and covers boron, silicon, and germanium. Silicon and germanium are borderline elements with metalloid characteristics. Both are important semiconductor materials, particularly silicon, which forms the backbone of the largest business in the world the electronic industry. All three materials are deposited by CVD on an industrial scale and a wide variety of CVD reactions are available. 

The transition elements comprise groups 3 to 12 and are found in the central region of the standard periodic table, an example of which is reproduced on the endpaper. This group is further subdivided into those of the first row (the elements scandium to zinc), the second row (the elements yttrium to cadmium) and the third row (the elements lanthanum to mercury). The term transition arises from the elements supposed transitional positions between the metallic elements of groups 1 and 2 and the predominantly non-metallic elements of groups 13 to 18. Nevertheless, the transition elements are also, and interchangeably, known as the transition metals in view of their typical metallic properties. 

Apart from the three broad categories of student conceptions discussed above, students displayed several inappropriate conceptions relating to the stractural properties of substances. For example, 14% of students suggested that Mg + ions were present in magnesium ribbon. A second example involved the chemical reaction between copper(II) oxide powder and dilute sulphuric acid. In this instance, 25% of students suggested that Cu + ions were present only in aqueous solution but not in the solid and liquid states. This view was rather unexpected because students had earlier been introdnced to ionic and covalent compounds. It is likely that students had merely rote-learned the general rale without sufficient understanding that ionic solids are formed between metallic and non-metallic elements. 

Ceramics are compounds of non-metallic elements and include the following materials used for chemical plant ... 

Although they are much more common than was at one time believed, molecules of the non-metallic elements with an LLP coordination number of greater than four are nevertheless relatively rare. They are very largely limited to the halides, particularly the fluorides, chlorides,... 

The yellow a-form is a powerful oxidant, reacting violently when heated with a variety of metallic and non-metallic elements. 

Non-metal element Compound with other elements... 

Fig. 1.15. The estimated non-metal element content of the primitive (X) and the modem (O) sea.

---