Mendeleev's table needed one important modification before it became the modern periodic table – the use of atomic number to order the elements. All atoms of the same element contain the same number of particles called protons, and this is called the element's atomic number. read more
The elements of period one will have only one shell, elements of period two will have two shells and so on. The first period of the modern periodic table is the shortest period as it contains only two elements. read more
The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties, whose structure shows periodic trends. read more