Developing the Periodic Table

By the 19th century scientists had discovered over 50 elements, many attempts had been made to put these elements into a logical order to reflect the similarities in their chemical properties.

Table of Contents

The early periodic tables were arranged strictly by atomic weight as protons, neutrons and electrons had not been discovered yet. Below is a summary of how the periodic table has changed over time to form the periodic table we use today.

Newlands Octaves

• Newton’s Law of Octaves . In 1864, an English scientist, John Newland proposed his ‘ law of octaves ’ where he arranged the elements in order of their atomic mass. Newland noticed that every 8th element had similar chemical properties.
• Newland’s Octaves. Newland arranged the discovered elements in order of atomic weight with H (Hydrogen) as the lowest then Li (Lithium) then Be (beryllium) and so on. Newland proposed that properties of every 8th element were similar for example Li (lithium) and Na (sodium).
• Problems with the Law of Octaves. However, many scientists did not accept Newland’s law of octaves because many new elements were still being discovered and did not fit in the table. Furthermore, all elements in his octaves did not have similar properties for example in the 7th octave O (Oxygen a non-metal) and Fe (Iron a metal).

Mendeleev’s Periodic Table

In 1869 Dimitri Mendeleev categorised the elements into ‘ Periodic System ’. This was a table of elements arranged according to atomic mass however there were many differences between Newland’s octaves and the Mendeleev’s periodic system.

Mendeleev’s main focus was arranging the elements based on similarities of chemical and physical properties . So he arranged the elements in a table, with vertical columns known as groups and these groups had elements with similar properties.

Mendeleev acknowledged that all elements had not been discovered yet, therefore left gaps to be filled in once they had been discovered. The gaps existed in certain groups with particular characteristics, therefore Mendeleev was able to predict the properties of these undiscovered elements. When these elements were discovered, his predictions were right and Mendeleev’s table was accepted by other scientists.

Rearranging the Position of Elements

• He did not stick to the strict order of arranging elements in order of increasing atomic mass. When Mendeleev organised elements in order of atomic mass, some elements did not fit the pattern of the group of increasing atomic mass. He rearranged these elements so that they would be placed in a group with similar properties.
• Iodine and Tellurium swapped positions. Iodine has a lower atomic mass than Tellurium , therefore it should be placed before Tellurium in the periodic table. However, Mendeleev saw that Iodine has similar properties to the elements in Tellurium’s group (7) such as fluorine, chlorine and bromine. Therefore, Mendeleev swapped around these two elements to ensure elements were in groups with similar properties.
• Explanation of Tellurium and Iodine order. We now know that the explanation of isotopes is the reason why iodine has a lower mass number than tellurium, even though it has a higher proton number.

The periodic table is a table that arranges all of the known elements in order of increasing atomic number. The purpose of the periodic table is to provide a way to organize and understand the properties of different elements.

The periodic table was developed by the Russian chemist Dmitri Mendeleev in 1869. Mendeleev’s periodic table was first published in a Russian scientific journal, and it quickly gained widespread recognition as a useful tool for organizing and understanding the elements.

Mendeleev developed the periodic table by organizing the elements based on their atomic mass and chemical properties. He arranged the elements in rows and columns, and he noticed patterns in the properties of elements that were in the same column. He used these patterns to predict the properties of elements that had not yet been discovered.

The key features of the periodic table include the arrangement of elements in order of increasing atomic number, the use of rows and columns to organize elements with similar properties, and the use of symbols and atomic numbers to identify each element. The periodic table also includes information about the elements’ atomic mass, electron configuration, and chemical properties.

The periodic table has changed since its development by Mendeleev, as new elements have been discovered and the properties of existing elements have been more thoroughly studied. The periodic table has also been modified to reflect our increasing understanding of atomic structure and electron configuration.

Students can use the periodic table to understand the properties of different elements, to make predictions about the properties of unknown elements, and to understand how elements react with each other to form compounds. By studying the periodic table, students can gain a deeper understanding of chemical concepts and be better prepared for questions related to this topic on their GCSE chemistry exams.

These questions and answers provide a comprehensive overview of the development of the periodic table, making it easier for 15-16 year old students to understand this concept as they prepare for their GCSE chemistry exams.