15. Read and translate the text

Inorganic molecules and compounds

Simple diatomic molecules of a single element are designated by the symbol the element with a subscript 2. That indicates that the element contains 2 atoms. Thus the hydrogen molecule is H₂; the nitrogen molecule, N₂; and the oxygen molecule, O₂. Polyatomic molecules of a single element are designated by the symbol for the element with a numerical subscript corresponding to the number of atoms in the molecule. Examples are the phosphorus molecule, P₄, and the sulphur molecule, S₈.

Diatomic covalent molecules, containing unlike elements, have a similar designation. The formula for hydrogen chloride is HCL. The more electropositive element is always designated first in the formula.

For polyatomic covalent molecules containing unlike elements, numerical subscriptions are used to designate the number of atoms of each element present in the molecule, for example, water, H₂. Again, as in diatomic molecules, the more electropositive element is placed first in the formula.

Notes to the text:

numerical – числовой

corresponding – соответствующий

unlike – различный

16. Find the pairs of the words with the opposite meaning:

single-atomic, first, less, unlike, absent, simple, compound, similar, more, polyatomic, present, last.

17. Match the words and word-combinations in a with their Russian equivalents in b

1. simple diatomic molecules	a. двухатомные ковалентные молекулы
2. diatomic covalent molecules	b. более электрополжительный элемент
3. molecules containing unlike elements	c. простые двухатомные молекулы
4. the number of atoms of each element	d. количество атомов каждого элемента
5. the more elektro- positive element.	e. молекулы, содержащие различные элементы

18. Form the antonyms with the help of the prefixes “de-“, “in-“, “dis-“, “un-“, “im-“, “ex-“:

cover, increased, organic, charge, possible, include, reversible.

UNIT II CHEMISTRY LABORATORY AND EXPERIMENTS

Grammar: There be, Modals

The Indefinite Pronouns

Text: Laboratory

1. Translate and memorize the following words.

escape	flask	funnel
pour	balance	glassware
ignite	crucible	odour
weigh	drawer	measure
provide	device	light
evaporate	burette	heat
serve	beaker	employ

2. Define the parts of speech and translate them without a dictionary.

to weigh – weighing – its weight – weightless – weightlessness – weighty; to measure – measure – measurement; define – definition – definite – indefinite – definitely; evaporate – evaporation – vapour(vapor); simple – simply – simplicity – simplify – simplification; to vary – variation – variety – various – variable; ignite – ignition.