Problem 72 - Introductory Chemistry Atoms First

Question

What would the charge on a ion be if, starting from the neutral atom: (a) You add three electrons. (b) You remove four electrons. (c) You add two neutrons to the nucleus.

Step-by-Step Solution

Answer

(a) The charge of the ion will be -3. (b) The charge of the ion will be +4. (c) The charge of the ion will be 0 (neutral).

Step 1: Case (a): Adding three electrons

If we add three electrons to a neutral atom, the number of electrons will be three more than the number of protons. Since electrons have a charge of -1, and protons have a charge of +1, the overall charge of the ion will be: Charge = (Number of protons) - (Number of electrons) For this case: Charge = (Number of protons) - (Number of protons + 3) = -3 The charge of this ion will be -3.

Step 2: Case (b): Removing four electrons

If we remove four electrons from a neutral atom, the number of electrons will be four less than the number of protons. Continuing with the same charge calculation as the previous case: Charge = (Number of protons) - (Number of electrons) For this case: Charge = (Number of protons) - (Number of protons - 4) = 4 The charge of this ion will be +4.

Step 3: Case (c): Adding two neutrons

In this case, we are adding neutrons to the nucleus of the atom. Neutrons are electrically neutral, meaning they do not have a charge. Thus, adding neutrons will not affect the charge of the atom. Consequently, the charge remains the same as that of the neutral atom: Charge = (Number of protons) - (Number of electrons) For a neutral atom, the number of protons and electrons are equal. Therefore: Charge = (Number of protons) - (Number of protons) = 0 The charge of this ion will be 0 (neutral).

Key Concepts

Understanding Electron Addition

Electron addition occurs when extra electrons are introduced to a neutral atom. Typically, a neutral atom has equal numbers of protons and electrons. This balance results in no charge on the atom. When electrons are added, the balance shifts.
Extra electrons provide additional negative charges. For example, adding three electrons will result in the ion having more negative charges than positive charges. Given that each electron carries a -1 charge, adding them leads the ion to achieve an overall negative charge.

• The formula for calculating the charge after electron addition is simple:
  \[ \text{Charge} = (\text{Number of protons}) - (\text{Number of protons} + \text{Added electrons}) \]
• Therefore, in the scenario of adding three electrons, the charge becomes \(-3\).

Exploring Electron Removal

Electron removal is the process of removing electrons from a neutral atom. Since electrons carry a negative charge of -1, taking them away increases the net positive charge of the ion.
In a neutral atom, the number of protons and electrons is the same, making the atom uncharged. When electrons are taken away, there are more protons than electrons.
For instance, removing four electrons increases the positive charge by four. This results in a positively charged ion.

• The charge can again be calculated using the formula:
  \[ \text{Charge} = (\text{Number of protons}) - (\text{Number of protons} - \text{Removed electrons})\]
• Following this for the scenario presented, the charge becomes \(+4\).

Effect of Neutron Addition

Unlike electrons and protons, neutrons are neutral. They do not carry any electrical charge. As such, adding neutrons does not alter the charge of an atom.
When neutrons are added to the nucleus, the mass of the atom increases, but its electrical charge remains unaffected.
Neutron addition is relevant for changing the isotope of an element but not for affecting its charge.

• For a neutral atom, the formula remains:\[ \text{Charge} = (\text{Number of protons}) - (\text{Number of electrons})\]
• Since neutrons don't affect the number of protons or electrons, the ion remains at a zero charge, indicating it's neutral.