What is the complete chemical symbol for the ion with 42 neutrons, a mass number of 79, and 36 electrons?

Answer 1

^A_ZX^C

For the above:

1. X=chemical symbol (H, He, etc.)
2. Determine this by looking at the atomic number (Z), which is the number of protons.
3. A=mass number. This is a whole number, and the mass number is equal to the protons+neutrons
4. Mass=(# of protons)+(# of neutrons)
5. Z=atomic number = the number of protons
6. C=Charge
7. Charge = (# of protons) - (# of electrons)

Mass (A) = 79

Neutrons = 42

Find the number of protons

Mass = protons+neutrons

79=protons+42

79-42=37 protons

Z=atomic number = 37, so it's Rb

Find the charge of the ion:

Charge=protons-electrons

Charge=37-36

Charge=+1

So,

A=79

Z=37

X=Rb

C=+1

⁷⁹₃₇Rb¹⁺

Answer 2

Hi, Brooks,

To determine any element's chemical symbol, one MUST know how many protons are in the nucleus. That is the atomic number, and that is what differentiates individual elements from one another. Of course, this is a "tricky" question - if they told you the atomic number, you could have just looked that up on a periodic table, and be done here! - so here is what they've provided you:

What is the complete chemical symbol for the ion with 42 neutrons, a mass number of 79, and 36 electrons?

The next most important part of this answer comes from the recognition that atomic mass number is ALWAYS to sum of an atom's protons and neutrons in the nucleus. Ah HA!! So, now you have both the mass number (79) and the number of neutrons (42), so the total number of protons - the atomic number - is simply 79-42 or 37 protons. A quick look at the periodic table indicates that the element with an atomic number of 37 is Rubidium ... but we're not done yet! Neutral rubidium (or Rb) has 37 electrons (as to be expected with 37 protons in the nucleus), but the ion described above has only 36 electrons. Therefore, with one proton more than the number of electrons, the complete chemical symbol for this ion would be: Rb⁺ to indicate that it is a singly positively charged ion (or cation, to be precise).

'Hope that helps,

Chris