Importance of Carbon Chemistry

By Lester E. Showalter

It is well known that the element carbon plays an important 1) r_le in the life on Earth. If all the carbon and carbon compounds were suddenly 2) rem_ved from the earth it would look like the 3) s_rface of the 4) mo_n. Many of the little every-day things would be 5) qu_te impossible without the element carbon. The importance of carbon chemistry for man is great. Every month 6) s_veral hundred new organic compounds are 7) prepa_ed.

In an ordinary pencil, for 1) _______, the inside of the pencil is made from 2) _______, which is an elementary form of carbon, the wood and the paint on the 3) _______ of the pencil are all carbon or 4) ________compounds. If carbon compounds were removed from the human 5) _______, there would be nothing left except 6) _______ and a small residue of minerals and the same is true for all 7) ______ of living matter.

There are nearly two 1) (millions, million) different carbon compounds to have been studied and 2) (describes, described) in the chemical literature with 3) (thousand, thousands) of new ones, which are reported every year. Although 4) ( there are, there is) 89 other naturally occurring elements, the number of known carbon compounds is many times greater than that of the known compounds which contain no carbon. The very large and important branch of chemistry, which studies and investigates carbon compounds, 5) (call, is called) organic chemistry. The name "organic" comes from the past when chemical compounds 6) (produced, produce) from ones-living matter were called "organic" and all other compounds were called inorganic.

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From The Nature Friends

27.05. 2008

Periodic Law

By Marilyn Senterfitt

Periodic law is a statement of a periodic recurrence of chemical and physical properties of the elements when the elements are ar­ranged in the order of increasing atomic number. The atomic number is the number of positive charges, or 1) p_otons, contained in the atomic 2) nucle_s or, 3) equ__valently, the number of negative charges, or 4) ele__­trons, outside the nucleus in a 5) ne__tral atom. Such an arrangement in the form of a table in which the groupings of elements having 6) simil__r properties are easily 7) identif__ed is called the periodic system or the periodic table.

The periodic law can be explained on the 1) ______of the electronic structure of the atom, which is believed to be the main 2) _______ underlying the chemical 3) ________ and many of the 4) ______ properties of the elements. In turn, the electronic structures of 5) _____ have been successfully accounted for by the quantum theory. D.I. Mendeleyev was the 6) ______ to state the periodic law 7) _______its present form.

D.I. Mendeleyev 1) (will propose, proposed) in 1869 that the properties of elements are periodic functions of the atomic weight and 2) (grouped, is grouped) the ele­ments accordingly in a periodic system. Before the work of Mende­leyev, however, a number of chemists had noticed certain relation­ships between the properties of elements and 3) (its, their) atomic weight. In 1829 J.W. Dobereiner 4) (states, stated) that there existed some three-ele­ment groups, or triads, in which the atomic weight of the middle element 5) (was, were) the average of the other two and the properties of this element lay between those of the other two. For example, calcium, strontium, and barium 6) (is forming, form) a triad.

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From The Nature Friends

27.05. 2008

Ester

By Peter S. Brubaker

It has already been explained, that an ester is the 1) prod_ct formed by the reversible reaction between an acid and an alcohol. If an acid and an alcohol are 2) mi_ed a condition of equilibrium will 3) eventuall_ be set up when the rates of the 4) dire_t reaction (esterification) and reverse reaction 5) (h_drolysis) are 6) equ_l. Any excess of water will diminish the 7) propor_ion of ester present at equilibrium.

An ester may be almost 1) _____ hydrolyzed if it is heated with water, provided that a large enough proportion of water is 2) _____. The hydrolysis is usually slow, but is catalyzed 3) _____ acids. It becomes complete if a dilute solution of an alkali is used instead of 4) _____, for the acid produced by hydrolysis is neutralized by the alkali as 5) __________ as it is formed, and so can take no further part in the reaction. 6) _______esters of organic acids are pleasant-smelling, volatile liquids and many of them are used in 7) ______ and in the production of artificial flavouring agents.

Ethyl acatale 1) (is, are) a typical example of an ester of an organic acid. It is 2) (form, formed) when acetyl chloride or acetic anhydride acts on ethyl alcohol. Ethyl acetate is prepared 3) (by, at) the interaction of alcohol and glacial acid in the presence of 4) (concentrating, concentrated) sulphuric acid. Ethyl acetate is a colorless, mobile liquid with a pleasant fruity odour. It is soluble in water and is miscible with alcohol, ether and chloroform, forming neutral solutions. When ethyl acetate 5) (is, have to) boiled with water under reflux condensation, it slowly 6) (undergoes, undergo) hydrolysis.

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From The Nature Friends

05.07. 2003