Particles in the atom and atomic radius — practice questions

For $^{35}_{17}Cl$:

• Protons = Atomic Number (Z) = 17
• Electrons = Number of protons (as it's a neutral atom) = 17
• Neutrons = Mass Number (A) - Atomic Number (Z) = 35 - 17 = 18

For $^{37}_{17}Cl$:

• Protons = Atomic Number (Z) = 17 (It's still chlorine)
• Electrons = Number of protons = 17
• Neutrons = Mass Number (A) - Atomic Number (Z) = 37 - 17 = 20

Note that both are isotopes of chlorine as they have the same number of protons but a different number of neutrons.

1. Symbol: Losing two electrons results in a 2+ charge. The symbol is $Mg^{2+}$.
2. Protons: The number of protons does not change when an ion is formed. Protons = Z = 12.
3. Neutrons: Neutrons = A - Z = 24 - 12 = 12.
4. Electrons: The neutral atom had 12 electrons. It lost 2, so the ion has 12 - 2 = 10 electrons.

So, the $Mg^{2+}$ ion has 12 protons, 12 neutrons, and 10 electrons.