Question #09e19

1 Answer
Dec 4, 2016

Answer:

#""_15^31"P"#

Explanation:

Isotope notation, which is used to describe isotopes of various elements, requires

  • the atomic number of the element, #color(blue)(Z)#
  • the mass number of the isotope, #color(red)(A)#
  • the chemical symbol of the element

http://chemkjj.blogspot.ro/2015/06/c1-12-proton-number-mass-number-ions.html

So, the first thing to do here is figure out the chemical symbol of the element. Grab a periodic table and look for the element that has

#color(blue)(Z) = 15#

This element is phosphorus, #"P"#, located in period 3, group 15.

Now, you know that its atomic number is equal to #15# and that its mass number is equal to #31#, so set up your symbol and add the two values as shown in the above image

#""_(color(Blue)(15))^color(red)(31)"P " -># this is the phosphorus-31 isotope

This particular isotope of phosphorus has #15# protons, just like all isotopes of phosphorus, and

#31 - 15 = "16 neutrons"#

inside its nucleus. The number of neutrons is given by the difference between the mass number and the atomic number.