Question

Give the number of protons and electrons in each of the following common ions: \(\mathrm{Na}^{+}, \mathrm{Ca}^{2+}, \mathrm{Al}^{3+}, \mathrm{Fe}^{2+}, \mathrm{I}^{-}, \mathrm{F}\), \(\mathrm{S}^{2-}, \mathrm{O}^{2-}, \mathrm{N}^{3-}\)

Short answer

Protons and electrons for each ion are determined by atomic number and charge adjustment.

Step-by-step solution

Understand the concept of ions

Ions are atoms that have gained or lost electrons, resulting in a net charge. Positively charged ions are called cations and they have lost electrons. Negatively charged ions are called anions and they have gained electrons.

Determine the number of protons

To find the number of protons, look at the atomic number of each element on the periodic table. It corresponds to the number of protons for the elemental form. This number does not change when the element forms an ion.

Calculate the number of electrons lost or gained

For a cation (positive charge), subtract the charge from the atomic number to find the number of electrons (since electrons are lost). For an anion (negative charge), add the charge to the atomic number (because electrons are gained).

Apply the concepts to each ion

Let's apply the above steps to each ion:- \(\mathrm{Na}^{+}\) (Sodium ion): Atomic number 11, so 11 protons and 10 electrons (because it lost 1 electron).- \(\mathrm{Ca}^{2+}\) (Calcium ion): Atomic number 20, so 20 protons and 18 electrons (because it lost 2 electrons).- \(\mathrm{Al}^{3+}\) (Aluminum ion): Atomic number 13, so 13 protons and 10 electrons (because it lost 3 electrons).- \(\mathrm{Fe}^{2+}\) (Iron ion): Atomic number 26, so 26 protons and 24 electrons (because it lost 2 electrons).- \(\mathrm{I}^{-}\) (Iodide ion): Atomic number 53, so 53 protons and 54 electrons (because it gained 1 electron).- \(\mathrm{F}\) (Fluorine atom): Atomic number 9, so 9 protons and 9 electrons (neutral atom).- \(\mathrm{S}^{2-}\) (Sulfide ion): Atomic number 16, so 16 protons and 18 electrons (because it gained 2 electrons).- \(\mathrm{O}^{2-}\) (Oxide ion): Atomic number 8, so 8 protons and 10 electrons (because it gained 2 electrons).- \(\mathrm{N}^{3-}\) (Nitride ion): Atomic number 7, so 7 protons and 10 electrons (because it gained 3 electrons).

Key concepts

Cations

Cations are positively charged ions. This positive charge occurs because the atom has lost one or more electrons. Unlike electrons, protons are not affected during the formation of cations, so the number of protons in the atom remains constant. Here's how it works:

• When an atom loses an electron, it becomes positively charged because there are more protons than electrons.
• This imbalance results in a net positive charge, creating a cation.

For example, the cation \((\text{Na}^{+})\) loses one electron, resulting in 11 protons and 10 electrons. Keep in mind that the cation's charge is shown as a superscript with a plus sign, indicating how many electrons have been lost.

Anions

Anions are negatively charged ions. They form when an atom gains extra electrons. Remembering that an electron is negatively charged will help you understand this concept:

• Extra electrons result in more negative charges than positive ones in the atom.
• This surplus of negative charge leads to the formation of an anion.

Take the \( \text{I}^{-} \) ion as an example. It has gained one more electron than the number of its protons, leading to 53 protons and 54 electrons. Anions carry a negative charge, shown as a superscript with a minus sign, indicating those additional electrons compared to protons.

Atomic Number

The atomic number is crucial in understanding chemical elements. It is the number of protons in the nucleus of an atom and remains unchanged, whether the element is in a neutral state or an ion:

• The atomic number is unique to each element and can be found on the periodic table.
• This number defines what the element actually is, like 11 for sodium or 26 for iron.

While electrons can be added or removed to form ions, the atomic number is the key to determining the base identity of an element.

Electrons

Electrons are the negatively charged particles in an atom, placed around the nucleus in various energy levels or shells. Their number can change when ions form:

• In cations, electrons are lost, reducing the overall negative charge.
• In anions, electrons are gained, increasing the negative charge as compared to protons.

Knowing the atomic number helps in calculating the electron count in ions: subtract the charge for cations or add the charge for anions. For example, calcium has the atomic number 20, and as \(\mathrm{Ca}^{2+}\), it has 18 electrons because two are lost in forming the ion.

Protons

Protons are positively charged particles found in the nucleus of an atom. Their count is fixed and equals the atomic number:

• Protons define the element, staying constant whether the atom is neutral or forms an ion.
• The number of protons equals the atomic number, making it a pivotal factor in identifying the element.

Even as electrons are added or removed in the formation of ions, the proton count, and hence the atomic identity, of the element remains unchanged. For instance, iron has an atomic number of 26, and thus every iron atom or ion will always have 26 protons.