1.3 Mendeleev's Table Flashcards
Mendeleev’s table
In 1869, Mendeleev arranged all the elements known at the time into a table:
He put the elements in order of the relative atomic masses
He checked the properties of the elements and their compounds
He swapped the places of some elements so that elements with similar properties lined up
He left gaps where he thought there were other elements, and predicted their properties
When these elements were discovered, Mendeleev’s predictions fitted the properties very well
Pair reversals
Mendeleev thought he had arranged elements in order of increasing relative atomic mass. It wasn’t always true because some of the positions of elements in some pairs were reversed. For example, he put tellurium in group 6 and iodine in group 7. This matched the properties of the elements and their compounds.
Iodine should have been first because its Ar is less.
Group 6 and 7 elements
Group 6 elements:
do not react with water
all react with oxygen (except oxygen itself)
All form compounds with hydrogen with the general formula: H2X
6 electrons in their atom’s outer shell
Group 7 elements:
all react with water
do not react with oxygen
all form compounds with hydrogen with the general formula: HX
7 electrons in their atom’s outer shell
Atomic number
The number of protons in the nucleus determines the atomic number of an element, which in turn determines its position in the periodic table since elements are arranged in order of increasing atomic number.
Groups and periods
Elements are arranged in order of increasing atomic number in horizontal rows called “periods” and elements with similar properties are placed in the same vertical columns called “groups”.
For example, elements in Group 0 are inert, meaning that they do not react with other elements.
Metals and non-metals
Metals are on the left hand side and in the centre, whereas non-metals are on the right hand side. Metals always give their electrons in a reaction with a non-metal, and non-metals always receive electrons.
