Isotopes and Nuclear Symbols

Sample Problem #3

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Problem

One of the harmful species from nuclear fallout is the radioactive isotope of strontium, ⁹⁰₃₈Sr (assume the super and subscripts line up). How many protons and neutrons are there in the nucleus of strontium-90?

Solution

The nuclear symbol indicates the composition of the nucleus. The atomic number (number of protons) is a subscript at the lower left of the symbol of the element. The mass number (sum of the protons and neutrons) is a superscript to the upper left of the element symbol. For example, the nuclear symbols of the element hydrogen are:

¹₁H, ²₁H, ³₁H

Pretend that the superscipts and subscripts line up on top of each other - they should do so in your homework problems, even though they don't in my computer example ;-)

Answer

The number of protons is given in the nuclear symbol as the atomic number, 38. Obtain the number of neutrons by subtracting that number of protons from the mass number:

number of neutrons = 90 - 38 = 52

38 protons, 52 neutrons

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