A neutral isotope has a mass number of 65 and 36 neutrons. Identify the element symbol of this isotope and determine the number of protons and electrons.

Answer 1

Hi Audrey Y.!

The mass number (A) of an atom is equal to the sum of the number of protons (the atomic number, Z) and neutrons in the nucleus of the atom.

A = Z + n

In our problem, we are given that:

1. The mass number, A, is 65
2. There are 36 neutrons

Let's take our equation above, rearrange it and solve for the number of protons.

A = Z + n => Z = A - n

<=> 65 - 36

Z = 29

Because the fingerprint for every element is its atomic number, we can identify which element we are dealing with. In other words, the number of protons is a unique property for each element. While we see different isobars (isotopes) for elements and we can ionize them yielding a charged species, still, the atomic number is like an "atomic DNA" that identifies the element uniquely.

An atomic number equal to 29 identifies copper as our element.

Moreover, we are given that the species we are dealing with is a neutral isobar. Which means the number of positive charges and negative ones cancel out. Because protons confer positive charge and electrons negative charge, we can deduce the number of electrons is equal to the number of protons. Therefore, there are 29 electrons present.

Hope this helps!

Cheers

Answer 2

Hi Audrey,

Every discovered (and undiscovered) element on the periodic table is uniquely defined by the number of protons that it has in its atom.

In atomic notation, the mass number is:

mass number = # protons + # neutrons

You are told that the mass number of this atom is 65 and has 36 neutrons, so

mass number = # protons + 36 = 65

# protons = 65 - 36 = 29

Looking at the periodic table, 29 protons is unique to the element Copper (Cu).

A neutral atom must have an equal number of negative charges (electrons) and positive charges (protons), so this Copper atom has 29 protons and 29 electrons.

So the complete notation for this atom is: ⁶⁵₂₉ Cu (nuclear notation) or Cu-65 (hyphen notation). The lack of a charge in this notation implies that the atom is neutral.