Complete the following table, showing the number of protons, neutrons, and electrons for the two most common isotopes of mercury (200^Hg and 202^Hg) in both the elemental and ion forms.

Question

In this compound, mercury forms an ion with a charge of +2, and sulfur forms an ion with a charge of −2. Complete the following table, showing the number of protons, neutrons, and electrons for the two most common isotopes of mercury (200^Hg and 202^Hg) in both the elemental and ion forms.

Isotopes Form Protons Neutrons Electrons

200^Hg Atom (charge=0)

Ion (charge=+2)

202^Hg Atom (charge=0)

Ion (charge=+2)

1. 202^ Hg (atom; charge=0): ?protons
2. 202^ Hg (atom; charge=0): ?neutrons
3. 202^ Hg (atom; charge=0): ?electrons
4. 202^ Hg (ion; charge=+2): ?protons
5. 202^ Hg (ion; charge=+2): ? neutrons
6. 202^ Hg (ion; charge=+2): ?electrons

Answer 1

Let's start off with defining what is an isotope. Sometime's due to natural decay or certain reactions an atom may either lose or gain neutrons. As a result the mass of the atom may increase or decrease. The mass of protons and neutron are close to 1 atomic unit (au) each while an electron is about 1/2000 au. Because the mass of an electron is so small we can neglect it when calculating the mass number of an isotope. So we can use the following equation establish some relationships between mass number, number of protons in an isotope (p), and number of neutrons in an isotope (n): mass number = p + n.

So with your problem we can determine the number of protons, neutrons, and electrons using this equation. We know that when the isotope in question has a neutral charge that the number of protons (p) and electrons (e) are the same. We will use the net charge equation (p - e = charge) to prove this. We can rearrange it to get p = e + charge. When the charge is 0 we get p = e + (0) = e. But when the charge is not neutral (0) we can rearrange the equation again to determine the number of electrons to get e = p - charge. By looking on the periodic table, Hg has 80 protons and we are told that the Hg isotope has a +2 charge. We can substitute our values into the equation to get e = 80 - 2 = 78. So the Hg and Hg²⁺ isotopes will have both have 80 protons while Hg has 80 electrons and Hg²⁺ has 78 electrons.

Now that we have established this we can move onto the mass number equation. According to the periodic table, the Hg atom has 80 protons. With this in mind we can rearrange the mass number equation to calculate the number of neutrons: n = mass number - p. Substituting our values for ²⁰⁰Hg we get n = 200 - 80 = 120. For ²⁰²Hg we get n = 202 - 80 = 122. So we now know that ²⁰⁰Hg has 120 neutrons and ²⁰²Hg has 202 neutrons.

You can use the explanations provided above to answer all of your questions completely and remember to use these two equations for future reference: p + e = charge and p + n = mass number.