1 6 POPULAR SCIENCE MONTHLY. 



+ 

 form the molecules of hydrogen which may be represented by (H, H) 



similarly for other gases. Certain neutral atoms such as those of 

 argon are monatomic and non-valent and these appear to be unable 

 to enter into combination either with each other or with other atoms. 

 Accordingly, in a mass of free hydrogen there are no free electrons and 

 all the positively charged and negatively charged H atoms are in union. 

 Hence the gas is a non-conductor of electricity. But we can make it 

 a conductor by heating it to a high temperature. The explanation of 

 this is that a high temperature dissociates some of the molecules into 

 atoms and these under the action of electric force move in opposite 

 directions, thus creating an electric current. Thus air at ordinary tem- 

 peratures is an almost perfect non-conductor, but at a white heat it con- 

 ducts electricity freely. 



The monovalent elements like hydrogen are those neutral atomic 

 structures which can lose one electron or take up one electron, becoming 

 respectively positive atomic ions and negative atomic ions. In the 

 same way the divalent elements such as oxygen are those neutral 

 atomic structures which can part with two electrons and take up two 

 and so on for trivalent, quadrivalent, etc., atoms. The work required 

 to remove the second electron probably is very much greater than that 

 required to remove the first. Hence in polyvalent atoms the valencies 

 have unequal energy values. 



Consider now a mass of intermingled oxygen and hydrogen con- 

 sisting of neutral molecules. The state is a stable one as long as all the 

 molecules are neutral. If, however, we dissociate a few of the hydrogen 

 and oxygen molecules by an electric spark or by heat then there is a 

 recombination. A positive oxygen ion unites with two negative hydro- 

 gen ions and a negative oxygen ion with two positive hydrogen ions 

 and the result is two neutral molecules of water. This combination 

 takes place because the union of oxygen ions with hydrogen ions to 

 form water evolves more heat and exhausts more potential energy than 

 the combination of oxygen with oxygen and hydrogen with hydrogen 

 ions in equivalent quantity. The energy set free by the union of the 

 and H is sufficient to continue the dissociation of further gaseous 

 molecules so the action is explosive and is propagated throughout the 

 mass. 



There is however a broad distinction between the elements in this 

 respect, viz. : that some atoms are prevalently electropositive and others 

 electronegative. A metallic atom for instance is electropositive, but the 

 atoms of non-metals are mostly electronegative. Moreover metals in 

 the mass are electrically good conductors, whereas non-metals in the 

 mass are non-conductors or bad conductors. This may be explained by 

 the varying degree of force required to detach electrons from neutral 

 atoms and conversely the varying degree of attachment of electrons 



