Question

# Uranium has at. no 92 and atomic weight $238.089$. Calculate the number of protons, neutrons and electrons in uranium atoms.

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Hint:Atomic number is the number of protons in the nucleus of an atom. Identity of an element is defined by the number of protons it has. Atomic weight is the total weight of an atom that is the total number of neutrons and protons. We can calculate the number of protons, neutrons and electrons if we know atomic number and atomic weight.

Proton is the particle with positive charge. It is found in an atom’s nucleus. The total number of protons in an atom is indicative of its atomic number. The property of atomic numbers is that it uniquely identifies chemical elements. In an uncharged atom, the number of electrons is also equal to atomic number. The atomic number of uranium is 92. Hence the number of protons in uranium is 92.
In an uncharged uranium atom, the number of protons and number of electrons are the same. Hence the total number of electrons in the uranium atom is 92. Atomic mass is the total number of protons and neutrons in an atom. Here while calculating atomic mass, electrons are not counted as their weight is negligible. So, the atomic weight of uranium is 238. The atomic weight that is 238 is equal to the sum of protons and neutrons. Protons in uranium are 92, hence the number of neutrons in uranium atoms is 238 minus 92 which is equal to 146.

In an uranium atom, there are 92 protons, 92 electrons and 146 neutrons.
Note:
Protons as positively charged particles were discovered by Goldstein, neutrons as neutral particles were discovered by James Chadwick and electrons were discovered by Thomson.