C1 Development of the Periodic Table (page 105) Flashcards
In the early 1800’s Elements were arranged by what?
Atomic Weight
Until quite recently, what was the two obvious ways to catergorise elements?
1) Their Physcial and chemical properties
2) Their Atomic weight
why did scientists have no idea of atomic structure, or of protons neutrons or electrons before 20th century?
Scientists had no idea of atomic structure, as it wasn’t discovered, so there was no such thing as atomic number to them. It was only in the 20th century after protons and elecrons were discovered that it was realised the elements were best arranged in order of atomic number
Before the 20th century what was the only thing scientist could measure regarding the periodic pattern?
they could only measure atomic weight, and so the known elements were arranged in order of atomic weight.
Where did the name ‘Periodic Table’ come from?
When scientists could only measure atomic weight, the known elements were arranged in order of atomic weight, this formed a periodic pattern, in the properties of the elements. this is where the name ‘periodic table’ comes from
Back in the early 1800’s early periodic tables were not complete, and some elements were placed in the wrong group. why is this?
This is because elements were placed in the order of atomic weight and did not take into account their properties.
in 1869, who overcame some of the problems of the early periodic tables by taking 50 known elements and arranging them into his Table of Elements (with various gaps in the table (see diagram on page 105 in book)
Dmitri Mendeleev
How did Dmitri Mendeleev arrange the elements on the periodic table, back in 1869?
He put the elements mainly in order of atomic weight, but did switch that order if the properties means it should be changed.
an example of this can be seen with Te and I - Iodine actually has a smaller atomic weight but is placed afer tellurium as it has similar properties to the elements in that group (see page 105 of book)
Why was gaps left in the periodic table when Mendeleev done the table?
Gaps were left in the table tomake sure that elements with similar properties stayed in the same groups.
some of the gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be.
When theywere found and they fitted the pattern, it helped confirm Mendeleev’s ideas.
For example, Mendeleev made really good predictions about the chemical and physical properties of an element he called ‘Ekasilicon’, which we know today as germanium
Was Dmitri Mendeleev correct to leave gaps in the periodic table in 1869? and why?
In the early 20th century, the discovery of isotopes was confirmed. that meant Mendeleev was correct not to place elements in a strict order of atomic weight, but to also take account of their properties. Isotopes of the same element have different masses, but have the same chemical properties, so occupy the same position on the periodic table
How were elements classified in the early 1800’s? (1 mark)
By Atomic Weight (1 Mark)
Describe two changes that Mendeleev made to early periodic tabes? (2 marks)
Eg; he left gaps in order to keep elements with similar properties in the same group (1 mark).
He switched the order of elements based on their properties, even if their atomic weights were no longer in order (1 mark)
