Modern periodic law

Definition of the modern periodic law

This modern law explains how the set of physicochemical properties of elements is a function of periodic atomic numbers. The atomic mass represents the mass contained in the total number of protons and neutrons in an atom. The atomic number represents the number of positive particles, i.e. protons, in a nucleus. It is also important to know that in neutral elements, the number of protons is equal to the number of electrons outside the nucleus. Concerning structure, the nucleus is inside an atom, while electrons orbit outside the nucleus. Electrons moving in an outermost shell have more freedom of movement, as they are less affected by the attraction to the nucleus. Since electrons are involved in chemical reactions, the properties of an element depend on the atomic number but not on the atomic mass. As mentioned above, the atomic number defines the number of electrons and/or protons present in a neutral atom (an un-ionised atom). Once scientists were able to explain the basic unit of the elements, quantum numbers and the way the elements are electronically configured, they defined the modern periodic law in the periodic table. Thanks to the periodic law, chemistry scientists found that there was a similarity between the 94 chemical elements found in nature. This allowed science to advance even further, as people became more curious about chemistry. Then, with the help of science, new chemical elements of artificial origin were created. This led to a new periodic table, which has its origins in Mendeleev’s periodic table but using the modern periodic law.

Modern Periodic Law

The globally used periodic table is the one that comes horizontal, in a long-form. Elements are sorted from left to right, having an increasing atomic number. In this type of periodic table, there are periods and groups. The groups are given by the vertical columns. Each group is made up of elements with a similar electronic configuration of their atoms. In the past these groups were called IA, up to VIIIA, then changing to IB…VIIB and 0. Nowadays, to simplify the terminology, the groups are denoted by integers from 1 to 18. On the other hand, horizontal rows represent the periods. These are seven horizontal rows in the periodic table. In this case, the periods are ordered by the principal quantum number ‘n’. This number is one of the four quantum numbers denoted n, l, m and s. The principal quantum number indicates which is the main electron shell. For example, if n= 2, this implies that the main shell of the atom is number 2. In a specific period, the electronic configuration of the valence shell varies from element to element. This is why elements can change their chemical properties over time. This is a result of the periodic gradation of their physical properties. This is a periodic property, which varies drastically within the periodic table from the elements on the right to those on the left. Classification of the elements in the periodic table: Having as a departure point the law of the modern periodic table, it will be sorted by the electron configuration. Taking into account the different electronic configurations, the elements in the periodic table can be classified into four: Noble gases: elements belonging to a group (column) 18 of the modern periodic table. They are known as noble gases because they do not interact or react with other elements. Within this group are neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). The first element is helium and has an electronic configuration of 1s². The other noble gases have a different configuration to helium but are common to each other. For these, the outer shell is configured as ns²np⁶. Their stability is because in these elements the octet is complete.

Representative Elements

These elements fall into the category of representative elements. In the case of the first and second group elements, they belong to the s-block. This means that these elements have an outer configuration of 1s²and 2s². For the other elements, i.e. in groups 13 to 17, it is known that they belong to the p-block. For this block, the external configuration has variations between ns²np¹ and ns²np⁵.

Transition Elements

Those known as transition elements are part of groups 3-12. For these, the outer shell is electronically configured as (n-1)d^1-10 ns^1-2. These elements are known as transition elements, which also belong to the d-block elements.

Inner Transition Elements

For this case, we have the lanthanides and actinides. These elements can be found at the bottom of the periodic table. They are known as inner transition elements. Within these elements, it is known that the electrons are partially occupying the 4f and 5f orbitals. Because of this, these elements often have several special properties.