Question

How many electrons are contained in each of the following ions? a. \(\mathrm{Fe}^{2+}\) b. \(C a^{2+}\) c. \(C O^{2+}\) d. \(C O^{3+}\) e. \(S^{2-}\) f. \(C I^{-}\) g. \(\mathrm{Cr}^{3+}\) h. \(\mathrm{K}^{+}\)

Short answer

The number of electrons in each ion is as follows: a. Fe²⁺: \(24\) b. Ca²⁺: \(18\) c. Co²⁺: \(25\) d. Co³⁺: \(24\) e. S²⁻: \(18\) f. Cl⁻: \(18\) g. Cr³⁺: \(21\) h. K⁺: \(18\)

Step-by-step solution

Finding the atomic number

For each ion, look up the atomic number in the periodic table or any reference material. The atomic number is equal to the number of protons in the neutral state of the element.

Finding the number of electrons in the ion

For each ion, add or subtract the number of extra electrons from the atomic number (number of protons) depending on the ion's charge. For positive ions, subtract the charge from the atomic number. For negative ions, add the charge to the atomic number. a. Fe²⁺: - Atomic number of Fe = 26 (26 protons) - Charge = +2 (Lost 2 electrons) - No. of electrons in Fe²⁺ = 26 - 2 = \(24\) b. Ca²⁺: - Atomic number of Ca = 20 (20 protons) - Charge = +2 (Lost 2 electrons) - No. of electrons in Ca²⁺ = 20 - 2 = \(18\) c. Co²⁺: - Atomic number of Co = 27 (27 protons) - Charge = +2 (Lost 2 electrons) - No. of electrons in Co²⁺ = 27 - 2 = \(25\) d. Co³⁺: - Atomic number of Co = 27 (27 protons) - Charge = +3 (Lost 3 electrons) - No. of electrons in Co³⁺ = 27 - 3 = \(24\) e. S²⁻: - Atomic number of S = 16 (16 protons) - Charge = -2 (Gained 2 electrons) - No. of electrons in S²⁻ = 16 + 2 = \(18\) f. Cl⁻: - Atomic number of Cl = 17 (17 protons) - Charge = -1 (Gained 1 electron) - No. of electrons in Cl⁻ = 17 + 1 = \(18\) g. Cr³⁺: - Atomic number of Cr = 24 (24 protons) - Charge = +3 (Lost 3 electrons) - No. of electrons in Cr³⁺ = 24 - 3 = \(21\) h. K⁺: - Atomic number of K = 19 (19 protons) - Charge = +1 (Lost 1 electron) - No. of electrons in K⁺ = 19 - 1 = \(18\)

Key concepts

Atomic Number

The atomic number is a fundamental concept in chemistry. It tells you how many protons are in an element's nucleus. Each element on the periodic table has its own unique atomic number. For example, oxygen always has an atomic number of 8, meaning it has 8 protons. This number not only identifies the element but also gives a glimpse into its properties. If you look at iron (\(\mathrm{Fe}\), its atomic number is 26, indicating it has 26 protons. The atomic number is crucial for determining the electron configuration in neutral atoms, as a neutral atom will have the same number of electrons as protons.

Ion Charge

Ion charge occurs when an atom gains or loses electrons. When electrons are lost, a positive ion, or cation, is formed. Conversely, when electrons are gained, a negative ion, or anion, forms. The charge of an ion is expressed with a plus (\(+\)) or minus (\(-\)) sign along with a number indicating how many electrons have been lost or gained.

• An ion like \(\mathrm{Fe}^{2+}\) is positive because it has lost two electrons, resulting in a \(+2\) charge.
• On the other side, \(\mathrm{S}^{2-}\) has a \(-2\) charge because it has gained two electrons.

Understanding ion charge is essential for predicting how ions will interact in chemical reactions and compounds.

Electron Counting

Counting electrons in ions involves a straightforward process. The goal is to find the total number of electrons after accounting for the ion's charge. Here’s how you approach it:1. Start by identifying the atomic number of the element, which tells you how many protons—and thus electrons in a neutral state—the atom has.2. Adjust this number based on the ion's charge: - For a positive ion (cation), subtract the charge from the atomic number. - For a negative ion (anion), add the charge to the atomic number.Let's consider \(\mathrm{Ca}^{2+}\):- The atomic number of calcium is 20.- Since it's a \(+2\)ion, we remove two electrons from the neutral state: \(20 - 2 = 18\).This method enables you to determine an ion's electron count by considering its charge and atomic number.

Protons in Ions

While the number of electrons can change in the formation of ions, the number of protons remains constant. Protons define the element and are not affected by chemical reactions. The stable number of protons means that ion formation does not affect an element's fundamental identity. - If you consider \(\mathrm{K}^{+}\), potassium will always have 19 protons, even if it loses an electron to become a cation.- Similarly, for \(\mathrm{Cl}^{-}\), chlorine maintains its 17 protons, regardless of the electron gain.The constancy of protons ensures that while ions have varied electron numbers, they retain the core characteristics of their elemental form.