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Atomic weights were not always known to the same precision that they are today. There were small errors of measurement associated with their determination, and larger errors -- a factor of 1.5 or 2 -- associated with an incorrect attribution of valence.
Mendeleev first formulated the Periodic Law, and then arranged the elements in a table according to the known values of atomic weight.
In doing this he first came across beryllium -- an element with chemical properties very similar to aluminium. This element had been assumed to have a valence of 3 (like aluminium) and an atomic weight of 13.5 g/mol. Mendeleev realised that this could not be the case, but that if he assigned it a valence of 2 and an atomic weight of 9 g/mol, it fitted into the same group as magnesium and calcium. In some ways this was not appropriate, because chemically beryllium had a much closer resemblance to aluminium than to magnesium. However some of the compounds of beryllium had crystal structures isomorphous with the corresponding magnesium compounds, and this convinced Mendeleev that he was right to make this change in the molecular weight (and valence) assignement. Today we know that he was quite correct in making this change.
The modern basis of the periodic law expresses it in terms of atomic number rather than atomic weight. There are just three cases among the elements where the atomic number order does not follow the atomic weight.
(1) element 18 is argon, atomic weight 40.0 g/mol; element 19 is potassium, atomic weight 39.1 g/mol. But fortunately for Mendeleev's peace of mind and the general recognition of the periodic law among chemists argon had not yet been discovered!
(2) element 27 is cobalt, modern atomic weight 58.9 g/mol; element 28 is nickel, modern atomic weight 58.7 g/mol. These two elements are very similar, and their atomic weights were at that time within experimental error of each other, so Mendeleev assigned both of the elements the same atomic weight, and correctly placed cobalt before nickel in his 1871 table.
(3) element 52 is tellurium, modern atomic weight 127.6 g/mol; element 53 is iodine, modern atomic weight 126.9 g/mol. This was a real problem for Mendeleev. Iodine was a very common material, but tellurium was rather rare and infrequently encountered.
It was very clear that iodine was closely related in chemistry to bromine and chlorine, while tellurium obviously fitted in with sulfur and selenium. But the then accepted values of atomic weight had Te at 128 g/mol while I was at 127 g/mol.
Mendeleev was deeply convinced that the atomic weight of Te should be less than that of I. Scraping the bottom of the barrel, he was able to come up with a determination by a Czech(?) mining engineer that put the atomic weight of Te at 125 g/mol. A heated debate ensued with several carefully carried out determinations suggesting values between 127.5 and 128.0 g/mol , and Mendeleev insisting that such a value could not be correct because "the Periodic Law is a Law of Nature".
What else can I help you with?
Did Mendeleev fix the problem of predicted where new elements would fit into the periodic table?
Yes, Dimitri Mendeleev did (accurately, I might add) predict where elements would appear in his table. He also correctly predicted some of the missing elements' properties, based on where they were positioned in his table.
The usefulness of Mendeleev's periodic table was comfirmed by?
Mendeleev's periodic table was confirmed to be useful because it accurately predicted the properties of elements that had not been discovered at the time. When new elements were discovered and found to fit into the gaps Mendeleev had left, it provided strong evidence for the effectiveness of his periodic table in organizing elements based on their properties. This confirmed the periodicity of elements and highlighted the power of the periodic table as a tool for understanding and predicting the behavior of elements.
Who recognized a pattern in the properties of the elements and made the first periodic table?
In 1869, a Russian scientist named Dmitri Mendeleev arranged the elements in a table according to their atomic mass, this was the first periodic table. However, a few elements didn't fit the pattern in Mendeleev's table, so a new table had to be made, and that table is today's periodic table which is arranged by atomic number, and not atomic mass.
What led Mendeleev to predict that some elements had not yet been discovered?
Mendeleev discovered gaps in his periodic table where elements should logically fit based on their properties and atomic weights. He predicted that these missing elements would eventually be discovered because there were clear patterns in the properties of known elements that suggested the existence of undiscovered elements to complete the table.
Mendeleev's pattern repeated after how many elements?
The properties were repeated after 8 elements.
What do elements fit into?
what did Mendeleev see that elements it into
Why were the elements important to Mendeleev?
Chemical elements arrangement was the object of study for Mendeleev.
Did Mendeleev fix the problem of predicted where new elements would fit into the periodic table?
Yes, Dimitri Mendeleev did (accurately, I might add) predict where elements would appear in his table. He also correctly predicted some of the missing elements' properties, based on where they were positioned in his table.
What evidence would have refuted Mendeleev's predictions?
A clear refutation of Mendeleev's predictions would have been discovering elements that did not fit into his periodic table based on atomic weight and properties. If the properties of elements did not repeat in a periodic manner when arranged by atomic weight, this would have refuted his periodic law.
The usefulness of Mendeleev's periodic table was comfirmed by?
Mendeleev's periodic table was confirmed to be useful because it accurately predicted the properties of elements that had not been discovered at the time. When new elements were discovered and found to fit into the gaps Mendeleev had left, it provided strong evidence for the effectiveness of his periodic table in organizing elements based on their properties. This confirmed the periodicity of elements and highlighted the power of the periodic table as a tool for understanding and predicting the behavior of elements.
Who recognized a pattern in the properties of the elements and made the first periodic table?
In 1869, a Russian scientist named Dmitri Mendeleev arranged the elements in a table according to their atomic mass, this was the first periodic table. However, a few elements didn't fit the pattern in Mendeleev's table, so a new table had to be made, and that table is today's periodic table which is arranged by atomic number, and not atomic mass.
What led Mendeleev to predict that some elements had not yet been discovered?
Mendeleev discovered gaps in his periodic table where elements should logically fit based on their properties and atomic weights. He predicted that these missing elements would eventually be discovered because there were clear patterns in the properties of known elements that suggested the existence of undiscovered elements to complete the table.
Why was mendeleev unable to inculde the elements of helium and neon or argon in his tabble?
Mendeleev was unable to include helium, neon, and argon in his table because they were discovered after his periodic table was published in 1869. These noble gases were isolated much later in the late 19th and early 20th centuries and did not fit into Mendeleev's original classification of elements based on their properties.
Mendeleev's pattern repeated after how many elements?
The properties were repeated after 8 elements.
Who arranged the elements by atomic mass and used it to predict properties of missing elements?
Independently by Dmitri Mendeleev and Lothar Meyer in 1869
Why did mendeleev leave gaps in the table?
Scientists suggest Mendeleev left gaps in the periodic table because Mendeleev knew the elements existed; however, was unable to prove it.
Mendeleev's name for a column of elements?
mendeleev's name for a column of elements was groups.
