C1 - Development Of The Periodic Table

Question 1

In the early 1800s how was the periodic table structured?

Answer 1

In order of the atomic weight.

(Early periodic table werent complete and some elements were placed in the wrong group.This is because elements were placed in the order of atomic weight and not accounted their properties)

Question 2

What did Dmitri Mendeleev do in 1869?

Answer 2

He took 50 known elements and arranged them into his ‘table of elements’ - with various gaps.

(Mendeleev put the elements mainly in order of atomic weight but did switch that order if the propeties meant it should be changed.An example of this can be seen with Te and I - iodine actually has a similar atomic weight after tellurium as it has similar properties in that group)

Question 3

Why were gaps left in Dmitri Mendeleevs table in 1869?

Answer 3

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 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 ekasilican,which we know today as germanium

Question 4

What did the discovery of isotopes prove about Mendeleev leaving gaps in his ‘Table of Elements’

Answer 4

He was correct not to place elements in a strict order of atomic weight but to also to take account of their properties.Isotopes of the same element have different masses but the same chemical so occupy the same position on the periodic table