Topic 1.13-1.20 - The periodic table

-He arranged the elements in order of increasing relative atomic mass. -He put elements with similar properties below each other into groups -He left gaps for yet to be discovered elements. -He switched the order of a few elements to keep the groups consistent

By looking at the chemical and physical properties of the elements next to the gap, he could also predict the properties of these undiscovered elements

Mendeleev thought he had arranged elements in order of increasing relative atomic mass but this was not always true because of the relative abundance of isotopes of some pairs of elements in the periodic table

The atomic number of an element is the same as the number of protons in its nucleus. In the modern periodic table the elements are arranged according to their atomic number - not their relative atomic mass.

-Elements are arranged in order of increasing atomic number, in rows called periods -Elements with similar properties are placed in the same vertical columns called groups

Metals are elements that react to form positive ions. They are found to the left and towards the bottom of the periodic table because they lose electrons in order to form these positive ions, forming an electronic structure that is stable. Non-metals are elements that do not form positive ions. They are found towards the right and top of the periodic table because they gain electrons in order to form negative ions, forming an electronic structure that is stable.

-The group an electron is in tells you how many electrons are in its outermost shell. e.g. group 1 elements have 1 electron in their outer shell. -the period an electron is in tells you which number shell an element’s outermost electron is in