History of the Periodic Table
Scientists hypothesized that element qualities are periodic functions of their atomic masses, thus Mendeleev arranged 63 elements in a vertical column called groups and horizontal rows called periods. However, this classification technique was unable to explain the positions of some elements, rare earth metals, and isotopes. As a result, it was rejected. So, in 1923, Henry Mosley introduced a new attribute of elements called “Atomic number.” He believed an element’s atomic number to be a more fundamental feature than its atomic mass.
According to Dobereiner’s Triads, when atoms are grouped in increasing atomic mass order, the atomic mass of the middle element is almost equal to the arithmetic mean of the other two, and its properties are intermediate between those of the other two, according to this law.
Mendeleev investigated the properties of all 63 elements known at the time, as well as their compounds. When he arranged the elements in increasing order of atomic mass, he discovered that elements with comparable qualities appear on a regular basis. He made this finding in the form of the following statement in 1869, which is known as Mendeleev’s Periodic Law.
Atomic Number
Atomic number of an element refers to the number of protons present in its nucleus. It’s also called the nuclear charge number and is symbolized by Z. In a nonionized atom, the atomic number equals the number of orbiting electrons.
The atomic number defines the identity of an element. For instance, carbon, with six protons, remains a carbon atom irrespective of how many neutrons it has neutron. The atomic number serves as the unique identifier for each element.