TH E ATOM 83 



A singly charged atom is an atom that has gained 

 or lost one electron; a double charge means the gain 

 or loss of two electrons, and so on. Through the loss 

 of electrons the atom acquires its positive charges; 

 and through the gain of electrons its negative charges. 

 The electropositive elements are the atoms with a 

 tendency to lose electrons; the electronegative elements 

 those with a tendency to gain electrons. 



Enormous energies are locked up in the atom, as 

 shown in the emission "with explosive violence" of 

 the alpha particle and the beta particle in radio- 

 activity. 



Some elements are simple, thus hydrogen, helium, 

 carbon, oxygen, and others; some elements (isotopes) 

 consist of atoms that, having the same physical and 

 chemical properties, differ in atomic weight. Thus 

 chlorine, atomic weight 35.46, is an isotope that 

 consists of chlorine atomic weight 35.0 and chlorine 

 atomic weight 37. (Aston.) Ordinary lead has 

 atomic weight 207.2; lead derived from radium, 206.0; 

 and lead derived from thorium, 207.9. 



All atoms are built on the same general plan. 



The atom is not an impenetrable structure. The 

 thermal agitation of molecules does not supply 

 sufficient energy to permit the interpenetration of 

 atoms. But an atom endowed with sufficient kinetic 

 energy, readily can enter another atom. Thus an 



