john newlands- 1863, every 8 elements similar (law of octaves). ordered due to by atomic mass. similar properties recur and intervals. not believed because some elements were in the same place. some were clearly in the wrong places (no similar chemical or physical properties).
dimitri mendeleev- 1869, a russian scientist.arranged by atomic mass but left gaps for the undiscovered due to similar properties. he ignored some atomic weights where they didnt fit. initially doubted but when new elements were discovered the properties he predicted were correct.
alexander emile beguyer de chancourtois- 1862, came up with a better idea but when his work was published his diagrams were left out.
john dalton-arranged elements in order of mass (table of elements).
modern periodic table- accepted but has limitations. with discovery of protons, neutrons and electrons we understand how the periodic table relates to the structure of the atom. ordered by atomic number, this gets rid of the problem of argon and potassium and iodine. the group- tells us how many electrons in outer shell. period- the amount of shells.
group 1 (alkali metals). this is a group of very reactive metals which increase going down the groups as the atom gets bigger the single electron is attatched to the neutron. they have low melting/ boiling point (decreases down the group). they are soft (get softer down the group). they are low density (first three float on water). they react to form 1+ ions and a white compound.silvery at first but tarnish with oxygen. react vigourously with water.react with hologens to form white chlorides that dissolve in water.