Topic 1 Development Of The Periodic Table Flashcards
Until recently what were the two obvious ways to categorise elements
Physical and chemical properties
atomic weight
When was it realise the elements were best arranged in order of atomic number
Only in the 20th century after protons and electrons were discovered
Why was atomic weight used to arrange the periodic table
Because it was the only thing they could measure
Why was it given the name periodic table
Because when the elements were ordered in atomic weight there was a periodic pattern noticed in the properties of the element
Why did the early periodic table not work
Some elements were missing or placed in the wrong group because they were placed an order of atomic weight not taking their properties into account
Who overcame the problems of the early periodic table by taking the 50 known elements and arranging them with various gaps
Dmitri Mendeleev in 1869
What did Mendeleev put the elements in order of
Atomic weight but did switch the order if the properties meant that it should be changed
E.g. this can be seen as iodine actually has a smaller atomic weight but is placed after tellurium as it has a similar properties of the elements in that group
Why were gaps left in Mendeleev table
To make sure the elements with similar properties stayed in the same group
 What did some of the gaps in the periodic table indicate
The existence of undiscovered elements an alarm for Mendeleev predict what their properties might be
What helps confirm Mendeleev’s ideas
When new elements were found they fitted the pattern for example Mendeleev made really good predictions about the chemical and physical properties of an element he called ekasilicon which is known as germanium
How did the discovery of isotopes in the early 20th century confirmed that Mendeleev was correct to not place the elements in a strict order but to also take into account their properties
Isotopes of the same element have different matters at the same chemical properties to occupy the same position on the periodic table
What were the dobereiner triads
He placed sets of three elements with similar chemical properties in the order of increasing atomic weight
Why did the Dobereiner triads not work
He fell to arrange all of the then known elements in a form of triads of chemicals having similar properties and he could only identify three triads
