Dmitri Mendeleev
Definition and meaning of Dmitri Mendeleev in chemistry.
Dmitri Mendeleev was a Russian chemist who lived from 1834 to 1907. In 1869 he published the periodic table of the elements. He arranged the known elements so that ones with similar behavior lined up in the same column.
In more detail
By the 1860s chemists knew of about 63 elements but had no good way to organize them. Mendeleev wrote each element on a card along with its atomic weight and properties, then sorted the cards until a pattern appeared. He ordered the elements by increasing atomic weight.
Each time he reached an element that behaved like an earlier one, he started a new row. Similar elements then stacked up into columns. His real breakthrough was leaving gaps.
Where no known element fit the pattern, he left an empty space and predicted what would fill it. He even estimated the missing elements' weights and densities, calling them eka-aluminium, eka-boron, and eka-silicon. He turned out to be right.
Gallium was found in 1875, scandium in 1879, and germanium in 1886. Each one closely matched his predictions, which convinced other chemists that the table described something real about matter. Mendeleev was not working alone in this.
Lothar Meyer reached a similar arrangement at about the same time. Mendeleev is the name people remember because he used his table to make predictions that later came true. The modern table differs in one important way.
It orders elements by atomic number, the number of protons in the nucleus, rather than by atomic weight. Henry Moseley showed in 1913 that atomic number is the property that really sets the order. That change fixed a few pairs Mendeleev had placed out of sequence.
Key facts
| Lived | 1834 to 1907 |
|---|---|
| Nationality | Russian |
| Known For | The 1869 periodic table of the elements |
| Key Insight | Left gaps and predicted undiscovered elements |
| Predictions Confirmed | Gallium 1875, scandium 1879, germanium 1886 |
| Ordering He Used | Atomic weight, not atomic number |
| Named After Him | Mendelevium, element 101 |
| Field | General Chemistry |
Mendeleev left a gap below silicon and predicted an element he called eka-silicon. He estimated its atomic weight at about 72 and its density at about 5.5 grams per cubic centimeter. In 1886 Clemens Winkler discovered germanium, which has an atomic weight of 72.6 and a density of about 5.3 grams per cubic centimeter. The match was close enough to settle any remaining argument about the table.
Frequently asked questions
Did Mendeleev discover any elements himself?
No, he did not discover an element. His contribution was organizing the elements that were already known and predicting ones that had not been found yet. Three of those predicted elements were discovered within about 20 years.
How is Mendeleev's table different from the one used today?
He ordered the elements by atomic weight. The modern table orders them by atomic number, which is the number of protons in an atom. Henry Moseley established that change in 1913, and it corrected a few pairs Mendeleev had to place out of order.
Why were the gaps in his table so important?
The gaps turned the table into a testable prediction rather than just a list. Mendeleev said exactly what the missing elements should weigh and how they should behave. When gallium, scandium, and germanium matched, it proved the pattern was real.
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Sources & references
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