How do we know this? Because the Periodic Table gives us THE MASS of a molar quantity, i.e. N_ANA or "Avogadro's number"Avogadro's number of ALL the elements. You got a Periodic Table beside you? You should have one because you are doing your chemistry homework.
And thus to get the number of copper atoms, we just find the molar quantity........
(3.4*g)/(63.55*g*mol^-1)xxN_A3.4⋅g63.55⋅g⋅mol−1×NA, where N_A="Avocado number"NA=Avocado number,
=6.022xx10^23*mol^-1=6.022×1023⋅mol−1.
And thus "number of copper atoms....."number of copper atoms.....
(3.4*g)/(63.55*g*mol^-1)xx6.022xx10^23*mol^-1-=3.22xx10^22*"copper atoms"3.4⋅g63.55⋅g⋅mol−1×6.022×1023⋅mol−1≡3.22×1022⋅copper atoms.
Now "Avogadro's number"Avogadro's number is admittedly a large number. We use it because N_ANA ""^1H1H atoms have a mass of 1*g1⋅g; alternatively, N_ANA ""^12C12C atoms have a mass of 12.00*g12.00⋅g. It is thus the link between atoms and molecules, what chemists theorize about and of which they conceive, with the macro world of grams, kilograms, and litres, what chemists measure out in the laboratory.
It will be worth your while getting your head around this "principle of equivalent mass"principle of equivalent mass, of how a given mass of elements or molecules constitutes a SPECIFIC NUMBER of elements or molecules. So please get it right!
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