Question

How many protons and electrons are in each of the following ions? (a) \(\mathrm{Be}^{2+}\) (b) \(\mathrm{Rb}^{+}\) (c) \(\mathrm{Se}^{2-}\) (d) \(\mathrm{Au}^{3+}\)

Short answer

(a) 4 protons, 2 electrons; (b) 37 protons, 36 electrons; (c) 34 protons, 36 electrons; (d) 79 protons, 76 electrons.

Step-by-step solution

Identify Element and Atomic Number

For each ion, determine the element symbol and find its atomic number from the periodic table. This atomic number will give you the number of protons in the atom. For example, Beryllium (Be) has an atomic number of 4; hence it has 4 protons.

Calculate Electrons for Neutral Atoms

For a neutral atom, the number of electrons equals the number of protons. For example, neutral Beryllium (Be) has 4 electrons.

Adjust for Ionic Charge

Add or subtract electrons based on the ion's charge: - For positive ions ( extsuperscript{+} charge), subtract the charge number from the number of electrons. - For negative ions ( extsuperscript{-} charge), add the charge number to the number of electrons. For example, Be²⁺ loses 2 electrons, so it has 2 electrons (4 - 2 = 2).

Apply Steps to Each Ion

Apply the above steps for each ion: (a) - Beryllium (Be), Atomic Number = 4. - Protons = 4, Neutral electrons = 4. Be²⁺, so Electrons = 4 - 2 = 2. (b) - Rubidium (Rb), Atomic Number = 37. - Protons = 37, Neutral electrons = 37. Rb⁺, so Electrons = 37 - 1 = 36. (c) - Selenium (Se), Atomic Number = 34. - Protons = 34, Neutral electrons = 34. Se²⁻, so Electrons = 34 + 2 = 36. (d) - Gold (Au), Atomic Number = 79. - Protons = 79, Neutral electrons = 79. Au³⁺, so Electrons = 79 - 3 = 76.

Key concepts

Protons

In every atom, the number of protons determines the identity of the element. Protons are positively charged particles found in the nucleus of an atom. The number of protons is unique for each element and is referred to as the "atomic number." For instance, Beryllium has an atomic number of 4, meaning it possesses 4 protons.

• Protons have a positive charge.
• The number of protons is equal to the atomic number of the element.
• They reside in the nucleus, along with neutrons.

Understanding the role of protons is vital as their number remains constant in all ions of the same element, despite changes in electron numbers.

Electrons

Electrons are negatively charged particles that orbit the nucleus of an atom. In a neutral atom, the number of electrons equals the number of protons, balancing the electrical charges. However, for ions, the electron count varies, reflecting the ionic charge of the atom.

• Electrons have a negative charge.
• In a neutral state, electron count equals proton count.
• Ions can gain or lose electrons, altering their total count.

For example, a neutral Rubidium atom has 37 electrons. However, when it becomes a Rb⁺ ion, it loses one electron, having 36 electrons instead.

Atomic Number

The atomic number is a fundamental characteristic of an element, showing the total number of protons within its atoms. It's key in characterizing and identifying elements in the periodic table.

• It is unique to each element.
• Equal to the number of protons.
• Denotes the position of an element in the periodic table.

For example, Selenium has an atomic number of 34, indicating it contains 34 protons in its nucleus. This number not only determines its identity but also reflects its position among other elements.

Ionic Charge

Ionic charge arises when an atom gains or loses electrons, transforming it into an ion. This charge can be positive if electrons are lost, or negative if they are gained. The magnitude of the charge indicates how many electrons are gained or lost.

• Ions with positive charge are called cations.
• Ions with negative charge are called anions.
• The charge impacts the electron count.

For instance, the Se²⁻ ion means it has gained 2 extra electrons compared to its neutral atom state, leading to an excess of negative charge.