Happy 150th birthday, periodic table
The periodic table is an icon of science. Its rows and columns provide a tidy way of showcasing the elements that make up the universe.
It seems obvious today, but it wasn’t to early chemists. That changed when Dmitri Mendeleev pondered ways to group the elements.
The Russian chemist spotted an elegant and powerful pattern: certain elements exhibited similar traits, and these traits varied regularly – or periodically – with increasing atomic weight.
So on February 17, 1869, Mendeleev published a chart of the 60-odd elements known at the time, sorted by their weights and properties. It is one of the greatest scientific contributions ever.
The journal Science is marking the 150th anniversary with a special issue about the table. Contributor Michael Gordin, a science historian at Princeton, answered questions.
Why has the periodic table endured for 150 years?
It’s an amazing tool that compresses a huge amount of information into one format. It’s one of the first things people learn about chemistry. It’s in every textbook.
How did it work?
The table is organised by increasing atomic weight, but broken into rows. When Mendeleev did that, he saw that certain elements have similar properties – they form acids that have similar strength, they form crystals that look the same.
So, in addition to increasing atomic weight, he saw that there is some other pattern that repeats.
What sets his table apart from other tables of the 1860s?
Mendeleev did all the elements known at the time. Previous people hadn’t done all of them because they weren’t sure about the atomic weights. Mendeleev guessed their weights.
Secondly, he predicted the existence of new elements. When those elements were discovered, his table stood out.
How did Mendeleev predict undiscovered elements?
When Mendeleev started lining up elements with similar properties into columns, he noticed that, in some places, an element seemed to be in the wrong place and should be one column over. When he moved it over, everything worked out. But then there’s a gap. And he’s like, ‘‘OK, how do I explain the gap?’’
He said, ‘‘Well, its atomic weight should be about this, because I can average from the elements around it and guess it.’’
Within 15 years, three of the elements he predicted were discovered. They had the properties he guessed.
What kind of guy was Mendeleev?
He was born in Siberia. He taught at the University of St Petersburg but travelled widely.
He was boisterous, funny, quick to lose his temper, but also charismatic and engaging. He was politically active. He was in the papers a lot.
After he finished the table, he kept all of his mail because he knew he would be famous.
Scientists didn’t understand atoms until after Mendeleev died. How did that change the table?
We now organise the table based on quantum theory – on the positions the electrons in the outer shell of an atom have. That explains their chemical properties because the electrons determine how they bind with other elements.
Mendeleev didn’t know that. The electron was discovered in 1897. When people discovered new things he couldn’t put in the table, he got frustrated.
Later, Niels Bohr, the Danish physicist, published a version of the periodic table that incorporates the quantum vision of the atom.
It silenced those who thought the table was a lucky guess.
– Los Angeles Times