Revision exercises

Ex.1. Answer the following questions:

1. In what physical states do halogens occur? 2. Why are halogens never found in nature in their native form? 3. What are the elements of the halogen family? 4. Where are organic compounds containing halogens used? 5. How are halogen derivatives classified? 6. Why are aryl halides insoluble in water? 7. What do physical and chemical properties of alkynyl halides depend on?

Ex.2. Match the words with their definitions:

1. halogens	a. the lightest halogen which exists as a highly toxic, pale yellow diatomic gas;
2. nonmetal	b. a compound added to manufactured materials that inhibit, suppress or delay the production of flame;
3. electronegativity	c. a chemical element that mostly lacks metallic attributes;
4. fluorine	d. a group in the periodic table consisting of five chemically related elements (chlorine, bromine, etc.);
5. propellant	e. a binary compound of which one part is a halogen atom and the other part is an element or radical;
6. flame retardant	f. a pressurized gas that is used to create movement of a fluid;
7. halide	g. a measure of the ability of an atom of one element to remove an electron from an atom of another element.

Ex.3. Say whether the following statements are true or false:

1. Iodine is the most reactive halogen. 2. The halogens are poor thermal and electrical conductors in all phases. 3. Halogens require one additional electron to form a full octet. 4. Elemental halogens are diatomic molecules with non-polar covalent triple bonds. 5. Fluorine is the least electronegative element in the Periodic Table. 6. Astatine is widely distributed in nature. 7. Compounds containing more than one kind of halogen are possible.

Ex.4. Insert the necessary word:

1. Halogens have relatively low melting and boiling points that ... steadily down the group. 2. The halogens have distinctive, unpleasant ... , and are toxic. 3. Halogens are so ... that all the elements except helium and neon react with at least one of the halogens. 4. Bromine consists of bromide ... which have been found in the sea. 5. The ... of iodine may increase if particular iodides are mixed in the solution. 6. Medicinal products containing ... are used to treat infections, allergies, and diabetes. 7. ... which contain chlorine, bromine, and iodine are a threat to the ozone layer. (solubility, odours, chlorine, salts, haloalkanes, increase, reactive)

Unit VIII nitro compounds

A wide variety of organic compounds contain nitrogen. In fact, the types of nitrogen compounds are so numerous and diverse that we shall be unable to consider them all.

Nitro compound is any of a family of chemical compounds in which the nitro group (−O−N=O) forms part of the molecular structure. The most common examples are organic substances in which a carbon atom is linked by a covalent bond to the nitrogen atom of the nitro group. The structure of a nitro group can be represented as a resonance hybrid of two equivalent zwitter ionic polar structures. The hybrid structure has a positively charged nitrogen and two equivalent negatively charged oxygens.