= (a) The table shows data about the physical properties of some elements.
Appearance at Melting point Boiling point
room temperature
in °C
in °C
green gas
red-brown liquid
dark grey solid
shiny solid
shiny solid
shiny solid
Element
Chlorine
Bromine
lodine
Lithium
Sodium
Potassium
-101
-7
114
180
97.8
63.5
-34
59
184
1342
883
759
Does the element
conduct electricity?
no
no
no
yes
yes
yes
Mendeleev put these elements into two groups in the Periodic Table.
He used their similarities and differences to put lithium, sodium and potassium in one group.
He put chlorine, bromine and iodine into another group.
Discuss which data in the table support, and which data do not support, Mendeleev's idea
of organising these elements into the two groups.