ARTICLES 53 



arranged in the ideal positions about the nucleus, which is the 

 reason for their stability and inactivity. 



With Hydrogen (N = i) the first element in the next 

 group, the conditions are very different. It has a single positive 

 charge and a single electron. Its positive and negative poles 

 form an electric doublet of high moment which tends to attract 

 all other bodies something like a small magnet. Thus atomic 

 hydrogen is very strongly adsorbed on surfaces. By sharing 

 their electrons, two hydrogen atoms can hold a stable pair, 

 and therefore the atoms form diatomic molecules. These 

 have an unusually weak external field, so that hydrogen is a 

 gas with a very low boihng-point. For Lithium (N = 3) the 

 nucleus has 3 positive charges surrounded b}^ 3 electrons. 

 Two of these electrons complete the first shell, forming 

 a kernel similar to the Helium atom, but with an extra 

 positive charge, which can hold an additional electron in 

 the second shell. This extra electron tends to make the 

 atom very active chemically. Like those of hydrogen, the 

 lithium atoms are electric doublets and attract one another. 

 However, owing to the greater size of the kernel compared 

 with the hydrogen nucleus, there is still a strong electric 

 field around a pair of atoms, so that they can attract a third, 

 and so on. Thus, lithium is a solid ; its atoms do not form 

 molecules, but the positive kernels and single outside electrons 

 arrange themselves in a space lattice in a manner quite similar 

 to the sodium and chlorine in a crystal of sodium chloride. 

 The single electrons, being surrounded on all sides by positive 

 charges, are free to move under an electric force, and metallic 

 lithium is a conductor of electricity. 



The chemical properties of lithium, beryllium, and boron, 

 are determined largely by their tendency to revert to the stable 

 form corresponding to helium. They are said to give up their 

 extra electrons to form stable arrangements with the electrons 

 of other atoms ; thus they have respectively unit, double, and 

 treble valencies. 



With Carbon (N = 6), Nitrogen (N = 7), and Oxygen 

 (N = 8), which have respectively 4, 5, and 6 electrons 

 in the outside shell, a tendency becomes manifest to take up 

 electrons to form stable octets. This opens up new possibilities 

 for the formation of compounds, and explains the remarkable 

 differences in the properties of these elementsl from those of 

 lithium and beryllium. 



With Fluorine (N = 9)''there are 7 so-called '' free " electrons 

 in the outer shell, and the octet is nearly complete. The 

 properties of fluorine are determined by its intense desire to 

 attain to these stable groupings. When brought into contact 

 with an atom having a single free electron, e.g. lithium, the 



