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The history of the periodic table

The history of the periodic table

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Explainer Video

Tutor: Aimee LeBrun

Summary

The history of the periodic table

​​In a nutshell

The periodic table is arranged in order of increasing atomic number. A scientist named Mendeleev organised the periodic table in this way.



Mendeleev's periodic table 

How did Mendeleev organise the periodic table?

  • ​Placed elements in order of increasing atomic mass 
  • Swapped the places of some of the elements depending on their properties 
  • Left gaps where he predicted other elements should go based on predicted properties 
  • Once elements were discovered they were placed into the gaps


​​Note: Mendeleev came up with an order for the periodic table before all of the elements had been discovered, hence why some gaps were left. 


Pair reversals

Mendeleev did not know about isotopes. The discovery of isotopes allowed for pair reversals. 

​

Example

The relative atomic mass of tellurium (TeTeTe) and iodine (III) are 128128128 and 127127127 respectively. ​However, Mendeleev placed TeTeTe​ before III in the periodic table (due to their properties). The most abundant isotopes of TeTeTe​ are Te−128Te-128Te−128 and Te−130Te-130Te−130​. The high abundance results in a higher relative atomic mass. But the atomic number of tellurium is 525252​ and iodine is 535353​, which supports the reverse order of elements in the periodic table. 



Atomic number

The periodic table is organised in order of increasing atomic number. The atomic number is the number of protons in the nucleus of an atom. The mass number is the number of protons and neutrons in the nucleus of an atom.



The periodic table


Chemistry; Key concepts; KS4 Year 10; The history of the periodic table

​

  • The periodic table is filled with elements 
  • Periods are the horizontal rows in the periodic table
  • Groups are vertical columns in the periodic table 
  • Metals are located to the left and in the middle of the periodic table
  • Non-metals are located to the right of the periodic table 
  • Elements with similar properties are placed in the same group


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Learn with Basics

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Naming chemical compounds

Unit 1

Naming chemical compounds

The modern periodic table

Unit 2

The modern periodic table

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The history of the periodic table

Unit 3

The history of the periodic table

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FAQs - Frequently Asked Questions

Where are metals on the periodic table?

Metals are located to the left and in the middle of the periodic table.

Who organised the periodic table?

Mendeleev organised the periodic table.

How is the periodic table arranged?

The periodic table is arranged in order of increasing atomic number.

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