Why are the elements sodium and chlorine in the same period of the Periodic table?

10 (a) Name an alkali metal other than lithium, sodium and potassium.
(b) Name an alkaline earth metals other than calcium, strontium and barium.
(c) Name one halogen other than chlorine, bromine and iodine.
(d) Name a non-metal having properties similar to carbon.
(e) Name a rare gas other than neon, krypton and xenon. 11 Explain why the following statements are not correct?
i)  All groups contain both metals and non-metals
ii) In group I, reactivity decreases with increases in atomic number
iii) Elements in a period become more metallic with increasing atomic number
iv) Atoms of elements in the same group have the same number of electrons.  2

What were the limitations of Dobereiner's classification of elements ?

3

What were the criteria used by Mendeleev in creating his periodic table ?