- Anomalies in the second period Even if we talk of alkalii metals, we can see that between them, there are rather significant differences. For example: two molecules of lithium hydroxide decompose at high temperature to form lithium oxide and water, while sodium hydroxide doesn't decompose. In the same manner two molecules of sodium hydride decompose to form two atoms of sodium and one molecule of hydrogen, whereas lithium hydroxide doesn't. Thanks to the small atomic volume of lithium and of its high electronegativity (in comparison to sodium), its salts are unstable for example: two molecules of lithium acid sulfide decompose at high temperatures in order to form lithium sulfide plus hydrogen sulfide. In the same way, at high temperature, lithium carbonate decomposes resulting from the reaction lithium oxide and carbon dioxide. To sum up, lithium resembles more to magnesium than to sodium. As a final example I shall say that lithium, at room temperature and normal pressure (standard conditions), reacts with nitrogen forming lithium azide. In the same way magnesium reacts in the same conditions with nitrogen forming magnesium azide. We can observe that not only lithium resembles on diagonal with magnesium, but also Berrilium has certain similarities to aluminium, Bohr to sillicium, carbon to phosphorus, nitrogen to sulfide and oxygen to chlorine.
- Anomalies in the first period I left this concept at the end because hydrogen (the only active nonmetal in the first group) resembles equally to alkalii and to halogens. The positive ion of hydrogen (which actually is the proton) takes the electronic configuration of alkalii and it forms a kind of hydroxide: water (H-OH), but it doesn't exist in this state, set free, in nature. Another argument against the resemblancy of the proton with alkalii is that the positive hydrogen ion is 100,000 times smaller than the lithium ion. The negative ion of hydrogen has the configuration of halogens and also a polarization tendency. As halogens do, H- forms salts with alkalii, but the ionic radii of H- is almost equal to the ionic radii of iodine. The explanation of this phenomena is that only one proton can't control at the same time two electrons which are repulsing each other. Therefore, the ionic volume of H- increases.
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