Chem revision y9 t2

Reactivity increases down the group 

unstable outer shells with only one electron 

hydrogen, lithium, sodium, potassium, rubidium caesieum, francium 

alkali metals 

react best with group 7

1808 - john dalton - table of elements   

1869 - dimitri mendaleev - periodic table with gaps left - a lot less elements were know at this time. At this point, the table criteria only really worked up untill calcium. the fact that not all atoms  did fit is now explained (partialy) by isotopes.

modern table

groups are the colums  and increase in electron shell number

periods are the rows and increase in electron outer shell number

low melting and boiling points

fluorine, chlorine, bromine, iodine, astatine

name comes from the greek for 'salt - forming'.

reactivity increases up the group

least rective elements 

these atoms havea fullouter shell and so have no tendency to gain or lose electrons.