Difference Between Mendeleev and Modern Periodic Table

Main Difference – Mendeleev vs Modern Periodic Table

The periodic table is the arrangement of chemical elements according to their chemical and physical properties. The modern periodic table was created after a series of different versions of the periodic table. The Russian Chemist/Professor Dmitri Mendeleev was the first to come up with a structure for the periodic table with columns and rows. This feature is the main building block for the modern periodic table as well. Mendeleev was able to identify that chemical properties of the elements began repeating each time after a certain number of elements. Hence, the term ‘periods’ came into use, resembling this character of repetition. The columns in the periodic table are called groups, and they group together elements with similar properties. The rows in the periodic table are called periods, and they represent sets of elements that get repeated due the possession of similar properties. The main difference between Mendeleev and Modern Periodic Table is that Mendeleev’s periodic table orders the elements based on their atomic mass whereas Modern periodic table orders the elements based on their atomic number.

What is Mendeleev Periodic Table

The basis of Mendeleev’s periodic table was categorizing the elements according to their physical and chemical characteristics with regard to their atomic weights. There were other scientists who have worked on tabulating information of the elements even before Mendeleev, however, he was the first scientist to come up with a periodic trend to predict the properties of elements which were not discovered at that time. Therefore, Mendeleev’s periodic table had empty spaces/gaps, so that these elements, once found can be then included. Gallium and Geranium were two such elements.

Also in some cases, Mendeleev didn’t strictly follow the rule of ordering the atoms according to their atomic weights; he placed the elements giving priority to their chemical properties, so they can be grouped accurately. The elements Tellurium and Iodine is a good example for this. Mendeleev’s first periodic table had the elements with similar properties grouped in rows. He then released a second version of his periodic table where the elements were grouped in columns numbered l-Vlll, depending on element’s oxidation state. However, Mendeleev’s periodic table didn’t support the existence of the isotopes. They are the atoms of the same element with differing weights.

Mendeleev Periodic Table

What is Modern Periodic Table

The basis of the modern periodic table is the atomic number of elements; the physical and chemical properties of the elements are treated as periodic functions of their atomic numbers. Therefore, it gives meaning to the electronic configuration of each element. The modern periodic table consists of 18 columns called groups and 7 rows called periods. The Lanthanides and the Actinides are arranged into different blocks. Therefore, the modern periodic table can also be viewed as blocks. It is built of four different blocks. The first two columns belong to the S block; columns 3-12 are in the d block, 13-18 are the elements of the p block, and finally the Lanthanides and the Actinides belong to the f block. The division into blocks is based on the orbital where the final electron gets filled up.

The periodic table has special trends and can be labelled for further differentiation. For instance, group 17 is called the halogens, and the group 18 is the noble gases. The first group is the alkali metals; the second is called the alkali earth metals, the d block of elements are known as the transition series. Around 4/5ths of the periodic table elements are metals. All the elements in the transition series and the f block, as well as the elements of the first two groups, are metals. The metallic character decreases when going from the left to right along a period of the periodic table. The atomic radius decreases, and the electronegativity increases when going from the left to the right along a period. The size of the atoms increases when going down any column of the periodic table.

Modern Periodic Table

Difference Between Mendeleev and Modern Periodic Table

Definition

Mendeleev’s periodic table was created on the basis of periodic functions of the elements, leaving room for future findings of the missing elements at that time.

The modern periodic table is the one used at the moment, as a collective improvement of the works of so many chemists and scientists in an effort to order the chemical elements to resemble the similarities in their properties.

Basis of Ordering

Mendeleev’s periodic table orders the elements based on their atomic weight.

Modern periodic table orders the elements based on their atomic number.

Gaps for Missing Elements

Mendeleev’s periodic table had gaps for the missing elements at that time.

Modern periodic table has no concept as such.

Number of Columns and Rows

Mendeleev’s periodic table has 8 vertical columns called groups and 12 horizontal rows called periods.

Modern periodic table has 18 columns called groups and 7 rows called periods.

Characteristics of Grouped Elements

Mendeleev’s periodic table has elements with dissimilar properties in the same group sometimes.

Modern periodic table’s elements have similar properties repeated at regular intervals.

Existence of Isotopes

Mendeleev periodic table doesn’t support the fact of the existence of isotopes.

Modern periodic table supports this fact as the classification is based upon the atomic number, rather than the atomic weight of the element.

Defining Atomic Structure

Mendeleev periodic table doesn’t support the concept of the atomic structure.

Modern periodic table supports this fact by grouping the elements in such a manner that their electronic configuration can be deduced easily.

Image Courtesy:

“Mendelejevs periodiska system 1871” by Original uploader was Den fjättrade ankan at sv.wikipedia – Källa:Dmitrij Ivanovitj Mendelejev (1834 – 1907). (Public Domain) via Commons 

“Periodic table (polyatomic)” by DePiep – Own work — “inspired by” free versions on Wikipedia/Commons.(CC BY-SA 3.0) via Commons