Mendeleev left gaps, where none of the known elements could fit. His
prediction was that these gaps would be filled at a later stage when new
elements were discovered. Today more than 100 elements are listed in the
In the periodic table, elements lying to the left of the
zigzag line are metals and those lying to the right are non-metals. The elements
lying close to the zigzag line exhibit properties of both metals and non-metals.
Metals are hard, malleable, ductile, lustrous, and good conductors of heat
Non-metals are dull, non-malleable, and non-ductile elements. They can exist
in all three states, solids, liquids, and gases. Non-metals are bad conductors
of heat and electricity except graphite.
So far, about 114 elements are known to us, out of which 80 percent are
metals and the rest are non-metals.