.Scientists who have contributed to the development of the modern periodic table.
John Newlands eighteen sixty four
- He arranged elements in order of atomic mass.
- Discovered the 'law of octaves' (every eight elements were similar. eg the first and the eighth and the second and ninth.)
- Noble gases had not been discovered because they are so unreactive.
- his ideas were rejected by the scientific community.
Main Problems with his work:
- he assumed all elements had been discovered. Left no gaps for new elements.
- grouped elements together which were unrelated.
Dimeetree Mendeleev eighteen sixty nine
- also arranged his table according to atomic mass
- put elements of similar reactivity in the same vertical group.
-left gaps for elements
-switched elements around if they did not fit the chemical patterns.
-called the horizontal rows periods
-left gaps in the periodic table and predicted the properties of the elements. he has been proven to be accurate.
-the modern periodic table has evolved from his table
Changes from Mendeleev's table and the modern periodic table
-the modern periodic table is arranged according to atomic number, not mass number.
-elements are arranged in order of ascending atomic number.
-generally, metals are on the left of the staircase with non-metals to the right.
-elements around the staircase show a mixture of properties and are called semi-metals or metalloids.
- the family of noble gases have now been discovered and added. they are very unreactive.
-the transition metals have been removed and placed between group 1 and 2.
-made up of over 100 elements. 11 are gases, two are liquids and 90 are solids.
-graphite is another exception of the classification of metals and non-metals. it is an allotrope of carbon. it is a giant molecular non-metal which exists in layers with a free electron between the layers which means graphite can conduct electricity which is a property usually only associated with metals. an allotrope is existence of an element in the same state but in a different form. sulphur is an alootrope.
Relationship between group number and number of outer shell electrons:
Outer shell electrons are used in bonding. the elements in the same group show similar reactivity. all the elements in the same group have the same number of outer shell electrons and hence similar reactivities.
the relative reactivity of some of…