Mendeleev arranged the elements in his periodic table in order of what?
Mendeleev's decision to leave gaps in his periodic table was supported by the discovery of what?
In the modern periodic table, elements are arranged in order of what?
How many periods does the periodic table have?
An atomic mass unit is what?
the twelfth the mass of a carbon -12
An element that is shiny and conducts electric currents is likely to be a what?
Copper is an example of what?
Elements that have the same number of valence electrons are what?
in the same group
The most reactive metals are the what group?
Which group are all gases at room temp.?
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