Here's the question you clicked on:
dandillilion
"Give the nuclear symbol for the isotope of gallium, Ga, that contains 40 neutrons per atom." If you want to tell me the answer that's great, but I'd much rather know the process to finding the answer.
nuclear symbols (also called isotopic notation) has 3 parts: \[^A_ZX\] Do you know that A, Z, and X stand for, and how to find them on the periodic table?
X is the symbol: in this problem, it's Ga Z is the atomic number. Gallium's atomic number is 31. Every element has a unique symbol and unique atomic number. If you know one of these 2, you can easily find both.
Thank you! What does A stand for?
A is the mass #, made up of the number of protons plus the number of neutrons in the nucleus. The mass # of an individual atom is always a whole number, but the average of all the isotopes of a particular kind of atom may be a decimal. The weights on the periodic table are a weighted average so they're (almost) all decimals. In this problem you're told there are 40 neutrons, and it's a gallium atom. Gallium has to have 31 protons, so the mass number (A) for this particular atom has to be 71. The answer in proper format looks like\[_{31}^{71}Ga\]31 protons for Z, (31protons + 40neutrons) for A, and Ga is the symbol
\[_{31}^{71}{\text{Ga}}_{40}\]