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development of a periodic table ((5) elements with similar properties form…
development of a periodic table
in the 1800s elements where arraned by atomic mass
Remember, scientists had no idea of atomic structure or of protons, neutrons or electrons, so there was no such thing as atomic number to them. (It was only in the 20th century after protons and electrons were discovered that it was realised the elements were best arranged in order of atomic number.)
Back then, the only thing they could measure was relative atomic mass, and so the known elements were arranged in order of atomic mass. When this was done, a periodic pattern was noticed in the properties of the elements. This is where the name 'periodic table' comes from..
until quite recently, there were two obvious ways to categorise elements: 1, Their physical and chemical properties 2, their relative atomic mass
Early periodic tables were not complete and some elements were places in the wrong group. This is because elemetns were placed in the order of relative atomic mass and did not take into account their properties.
Dmitri Mendeleev left gaps and
predicted new elements
Mendeleev put the elements mainly in order of atomic mass but did switch that order if the properties meant it should be changed. An example of this can been seen with Te and I- iodine actually has a smaller relative atomic mass but is placed after tellurium as it has similar properties to the elements in that group.
Gaps were left in the table to make sure that elements with similar properties stayed in the same groups. Some of these gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be. When they were found and they fitted the pattern it helped confirm Mendeleev's ideas. For example, Mendeleev made really good predictions
In 1869, Dmitri Mendeleev overcame some of the problems of early periodic tables by taking 50 known elements and arranging them into his table of elements- with various gaps as shown
5) elements with similar properties form columns
6) these vertical columns are called groups
4) metals are found to the left and non metals to the right
7)group number tells you how many electrons in the otter shell
3) if it wasn't for the periodic table organising everything.
8) if you know the properties of ne element you can predict properties of the rest in that column
2) in the periodic table the elements are laid out in order of increasing atomic protons numbers arranged the elements like this means there are repeating patterns in the properties of the element.
9) can predict the trends in reactivity eg group 1 elements get more reactive as you go down.
1) there are 100 ish elements which all materials are made up of
10)the rows are called periods each new period represents another fell shell of electrons