Answer:
Step-by-step explanation:
But when it comes to the word atom, we have to go to ancient Greece of 400 B.C. And there was a brilliant philosopher named Democritus, and he proposed the Greek word atomos, which means uncuttable. And so as he explained, all matter was eventually reducible to discrete, small particles or atomos. Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table. Electrons that have full outer shells have more in common with each other than those with partially full outer shells. The more full the outer shell is, the more stable the element.By having the periodic table laid out in the shape of a castle, scientists can easily observe each element and its properties. Heavier elements have more shells that can hold larger numbers of electrons. What really matters for each element's behaviour, however, is how many electrons it has in its outer shell. That number tends to fit nicely with the way the table is arranged, namely to place elements with similar properties in the same group.