Development of the periodic table
The modern periodic table was developed by many people in different times to become what is it today.
- JOHN DALTON- Arranged according to atomic mass that he found out by testing the known elements' reactions.
- JOHN NEWLANDS- Made a lot of mistakes as he was rushing. Brought about 'Law of Octaves' but this law was not accepted as all the elements did not follow the pattern. This was because many elements were not discovered.
- DIMITRI MENDELEEV- Left gaps on the periodic table for undiscovered elements and arranged elements according to atomic mass.
Scientists now use ATOMIC NUMBER to arrange the elements.
Group 1- Alkali metals
- More reactive as you go down as atoms get bigger
- Boiling and melting points decrease as you go down
- All have low density, and lithium and potassium float on water
- Can only form ionic bonds
- React with water to form hydrogen. The bottom three elements react more vigorously.
REMEMBER: The bigger the atoms the MORE reactive. This is because there are more shells, and the electrons on the outer shell are less attracted to the nucleus. They are, therefore, easily lost.
Group 7- Halogens
- Less reactive as you go down
- Can do both covalent and ionic bonds
- Poor conductors
- Melting and boiling points increase as you go down