English for chemists

Scction II
Упр. 1. Прочтите заглавие текста 12В. Скажите, чем, по вашему мнению, он б>дет отличаться от текста 12А.
Упр. 2. Назовите значения следующих интернациональных слов:
act, constant, composition, formula, experimentally, empirical, inorganic, crystalline, equivalent, sum, proportion, real, alternatively
Упр. 3. Определите значения выделенных слов по контексту. Сино­ нимы в скобках помогут вам.

1. 
   An empirical formula should be written with brackets (HgO)x.
   

2. 
   Mendeleyev assumed (supposed) the existence of yet undiscovered elements. 3. Originally (at first) oxygen was callcd “inflammable air”.
   

4. 
   The symbol for mercury is Hg. 5. The law of constant composition was known, therefore (that is why) it was possible to use a formula for a compound. 6. The formula for ammonia is NH}. 7. A molcculc of a
   

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compound is defined (is dcscribcd) as the smallest part of a compound that can exist as a free and separate substance.
Слова к тексту:
the very — сам no ссбс; equal — равный; determine — определять; relative — относительный; strictly — строго; it makes no claim — не пре­ тендует; perfectly — совершенно; entity — нечто реально существующее
Text 12 В
Прочтите текст про себя (контрольное время чтения — 4 минуты).
Chemical Symbols for Representing Compounds
It is a short step from using a symbol for an element to using a formula for a compound. However, it is often forgotten that the very act of writing the formula for a compound assumes the law of constant composition. HgO originally meant “some of a compound containing equal numbers of mercury and oxygen atoms”. A formula used in this way is referred to as an empirical formula, for it contains only the cxpcrimantally determined ratio of the relative numbers of atoms of different elements in the compound, but makes no statement about how many atoms there are in one molecule. An empirical formula should be written with brackets (HgO); to show that it makes no claim to represent one molecule of the substance; but for inorganic solids where there is seldom a method of determining *, the brackets are never used.
A molecule of a compound is defined as the smallest part of a compound that can exist as a free and separate substance. For crystalline solids in which one atom is surrounded by several equivalent neighbours, the word “molecule” has no well-defined meaning. Thus, the formula HgO refers to a gram-molccular weight of mercuric oxide, whereas the gram-molecular weight is the sum of gram-atomic weights of the elements in the proportions in which they occur in the compound. For example, zinc has a gram-atomic weight of 65 g and chlorinc a gram atomic weight of 35.5 g, so the gram-molecular weight of zinc chloride (ZnCb) is 135 g.
For gases, the molecule is a perfectly real entity, and the molecular weight of any volatile substance defined as
weight of 1 molecule
weight of V|2 atom of carbon 12
can be measured experimentally. Therefore the formula NHj can either refer to one molecule of ammonia, containing one atom of nitrogen, and three atoms of hydrogen, or, alternatively, to one gram-molccular weight of ammonia.

Though the terms “gram-molccular weight” and “gram-atomic weight” arc no longer used by chemists, it is interesting to know how the idea

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developed. At present, (he term “mole” (mot) is usually used to name the quantity of a substancc.
Упр. 4. Оправдались ли ваши предположения насчет отличия по содержанию текста 12 В от текста 12 Л?
Упр. 5. Разделите текст на тематические части и озаглавьте их.
Упр. 6. Скажите, что говорится в тексте:
1) о том, что необходимо было знать, чтобы написать формулу со­ единения символами; 2) о значении эмпирической формулы; 3) об упот­ реблении скобок при написании эмпирической формулы; 4) как опре­ деляется молекулярный вес летучих веществ; 5) что обозначает формула аммиака.
Упр. 7. Найдите в тексте отрывок, где дается определение молеку­ лы и описываются особенности употребления формул для обозначения твердых веществ. Переведите этот отрывок на русский язык.