Central High School - Centralian Yearbook (Kansas City, MO)

 - Class of 1902

Page 80 of 126

 

Central High School - Centralian Yearbook (Kansas City, MO) online yearbook collection, 1902 Edition, Page 80 of 126
Page 80 of 126



Central High School - Centralian Yearbook (Kansas City, MO) online yearbook collection, 1902 Edition, Page 79
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Page 80 text:

Department of Chemistry. The Ionic Theory and Some of Its Agzpl-ications. UST a century ago John Dalton was striving to prove his famous atomic theory, which he gave to XX the scientific world in 1807. To-day Dr. Loeb, of Chicago University, is rv working hard, with success X mf? ' - 'ff ' " ' A seemingly not far distant, proving his theory of the ion's relation to life. Dalton believed that the atom fthe smallest conceivable division of any elemcntj has a definite relative weight as compared with that' of hydrogen, which he assumes to be 1, and that the composition of a chemical compound is constant, that is, that the elements of which it is composed, always unite in a definite proportion. To be able to see clearly the difference between a compound and an element, a definition of the terms becomes necessary. An element is "one of the ultimate, homo- geneous substances of which anything is composed," or to make it clearer, any substance which cannot be divided into two or- more simpler substances. A compound is a substance composed of two or more elements, chemically united. Now, as Dalton said, the composi- tion of a chemical compound is con- stant. Taking water, HZO, for exam- ple, which we know is composed of two parts of hydrogen to one of oxygen, we find that the smallest conceivable division of this compound, the mole- cule, still contains two parts of hydro- gen to one of ojtygen. These parts which compose the molecule are atoms. It has been found that Dalton did not go quite far enough in his theory of the atoni-tliat an atom of one element docs not always replace onek atom of another element, as he believed, but may replace several, according to their respective atomicities or valence. Va- lence is measured by the power of an atom to combine with hydrogen. By hydrochloric acid, HCI, we see that the valence of the chlorine atom is oneg in the case of water, HZO, the hydrogen atom is shown to have a valence of two, and by carbon dioxide, CO2, the valence of the carbon atom is proved to be four, since it combines with two atoms of oxygen, and we have just shown the valence of the oxygen atom to be two. Valence is sometimes repre- sented by arms or bondsg an atom of carbon has four arms, an atom of oxy- gen two, hydrogen 0110, etc. This va- lence bears a close relation to the ion, which I shall consider next. If two salts are mixed together, a re- action seldom takes place immediate- ly, or if it does, the action is weak, but if one or both the salts be in the form of an aqueous solution, a reaction -30- two are ed, phyt at t cess fami the comy wher pass in tl

Page 79 text:

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Page 81 text:

nr rle Q- 0- ts is. ot of nt of ut Dir 3- an By he in en of he ed -svo st: JIT1 :re- of y- a- Jn, re- te- k 3 he on takes. plaee at once. When a salt or 2111 aeid is dissolved in water, the atoms are dissociated or torn apart, Then when another salt is added the dissociated atoms are free to 4-Ombiug with others and forin a new eompound. Although sonicwliat dissociated in the form ot a dry salt, tl1e atoms are not enough so to react to any great extent, Now, WllCll a solution is t.U!'Illt'ti and the atoms are dissociated, the violence of tl1e tearing apart electrifies them, one set heeoining charged with posi- tive electricity, the otl1er with negative. These electrified atoms are called "ions,'1 a11d the process hy wl1icl1 they become electrified f'ionization." Suppose tl1at we have a solution of co1nn1on salt, sodium chloride, NaCl. In forming the solution, the sodium atoms become charged witl1 positive electricity a11d the chlorine atoms with negative electricity. lf we place tl1e two ends of a copper wire into the solu- tion, a. current of electricity is started, just as in the case of a voltaie cell, ex- cept that in this case the current is many times smaller. Metallic atoms are always charged positively, and non- mctallie atoms negatively. Surround- ed, as the ionic theory is, in a meta- physical fog, o11e is naturally surprised at the simplicity of its proof-a pro- cess with wl1iel1 many ot' us are very familiar-electrolysis. When we used the eleetrolytie apparatus to prove the composition of water, we noticed that when the current of electricity was passed tlirougrh the 0lCl.'tI'Ul.YtO, which in this ease was water, the oxygen col- leeted i11 ttltlt side ot the 'U-sliaped tulle at wl1icl1 the eurrent entered- -the teriniiial lCl1OWI1 as the anodeg and that the llAVtll'0Q'U11 passed to the terminal where the current passed out-the eatliode. Now tl1e eathode is the neg- ative pole Zllld the anode the positive pole. llydrogen, altliough a gas, is sometiines regarded as a metal, and we saw that it collected at the cathode or negative pole. All metallic ions do, and for this reason are called cathions. The oxygen collected at the anode or positive pole, as non-metallic ions al- ways do, hence are known as anions. Every one is tlilllllliill' with the fact that bodies oppositely electrified at- tract each otl1er Illld those electrified alike repel. Then since the oxygen ions were attracted hy the positive pole, they must he negatively charged and since the hydrogen ions collect at the negative pole, we k11ow that they are positively electrified. Had we used a solution ot' any salt or acid the results would have lieen the same. lls- ing a solution of sodium chloride, for example, the sodium would have col- leeted at tl1e negative pole and the chlorine at tl1e positive one. But if after electrolysis l1ad been completed, the current were turned off and the solution allowed to evaporate, the so- dium and chlorine ions would have re-eo111hi11ed to form the original salt. 'l'he ionic theory aids the student of eliemistry much in interpreting lllillli' of the phenoiiiena with which he meets from time to time. For in- stance, he knows that concentrated sul- ,.31-

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