SILICON, TITANIUM, BORON
| SYMBOL | ATOMIC WEIGHT | DENSITY | CHLORIDES | OXIDES | |
| Silicon | Si | 28.4 | 2.35 | SiCl4 | SiO |
| Titanium | Ti | 48.1 | 3.5 | TiCl4 | TiO |
| Boron | B | 11.0 | 2.45 | BCl3 | B2O3 |
General. Each of the three elements, silicon, titanium, and boron, belongs to a separate periodic family, but they occur near together in the periodic grouping and are very similar in both physical and chemical properties. Since the other elements in their families are either so rare that they cannot be studied in detail, or are best understood in connection with other elements, it is convenient to consider these three together at this point.
The three elements are very difficult to obtain in the free state, owing to their strong attraction for other elements. They can be prepared by the action of aluminium or magnesium on their oxides and in impure state by reduction with carbon in an electric furnace. They are very hard and melt only at the highest temperatures. At ordinary temperatures they are not attacked by oxygen, but when strongly heated they burn with great brilliancy. Silicon and boron are not attacked by acids under ordinary conditions; titanium is easily dissolved by them.