Visualize a carbon with its four bonds being two methyl (CH3) groups and a double-bonded oxygen (called a keto group.) This is urea. Replace the oxygen with a sulfur (which is right under oxygen on the periodic table, and it is thiourea. The “thio” term means sulfur.
Just being simple.
So as we know from our basic organic knowledge.
“This" word means sulphur.
So the main difference between the urea and thiourea is that thiourea contains sulphur atoms, whereas urea didn't.
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Urea NH2CONH2 and thio urea is NH2CSNH2
If the oxygen atom in the urea molecule replaced by sulfur atom (thio) then it is thiourea