We cannot group metals and non-metals on the basis of their physical properties only because there are many exceptions both in metals and non-metals. For example,
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(i) All metals except mercury are solids.
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(ii) Metals have generally high melting points but gallium and caesium have very low melting points.
(iii) Metals are hard but alkali metals like lithium, sodium and potassium are so soft that they can be cut with a knife.
(iv) Non-metals are dull but iodine is lustrous.
(v) Non-metals are bad conductor of electricity but carbon in the form of graphite is a conductor of electricity.
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(vi) Most solid non-metals are soft but carbon in the form of diamond is the hardest natural substance.