Question

One isotope of a metallic element has the mass number 65 and 35 neutrons in the nucleus. the cation derived from the isotope has 28 electrons.

a. what is the symbol for the element?
b. what is the charge?

Answer 1

a. You determine element by the number of protons the element has. Let's first find that:
What do you know?
Mass number : 65
Neutron number: 35
If mass number is Protons + Neutrons, we can find # of protons through subtracting:
65 - 35 = 30 Protons.
Look on your periodic table. Which element has 30 protons? (30 is also the atomic number if that helps).

b. Charge is the difference between negative electrons and positive protons, right?
Because we know the numbers for both, this is easy:
28 electrons compared to 30 protons
30 - 28 = 2 difference
Since there are more protons, you would have a positive charge of 2. :)