That means selenium has 2, 8, 18 and 6 electrons in its first, second, third and fourth atomic orbital, respectively. When Mendeleev first published the original periodic table in 1869 ...
A constraint is an SQL object that helps define the set of valid values in the table in various ways. There are two ways to define constraints: table constraints and column constraints. A column ...
The alkaline earth metals represent the second column on the periodic table. Its six elements extend from beryllium (Be) to radium (Ra). These metals are named for forming basic solutions when put ...