Question

Determine the number of valence electrons present in each of the following metal ions: (a) \(\mathrm{Co}^{2+}\); (b) \(\mathrm{Mo}^{4+}\); (c) \(\mathrm{Ru}^{4+}\); (d) \(\mathrm{Pt}^{2+} ;\) (e) \(\mathrm{Os}^{3+}\); (f) \(\mathrm{V}^{3+}\).

Short answer

The number of valence electrons for the ions are: (a) Co^{2+}: 1, (b) Mo^{4+}: 10, (c) Ru^{4+}: 12, (d) Pt^{2+}: 16, (e) Os^{3+}: 13, (f) V^{3+}: 2.

Step-by-step solution

- Covalent Electrons for Cobalt (Co)

Cobalt (Co) is in the 9th group of the periodic table and has an atomic number of 27. It therefore has 27 electrons. The neutral Co atom has 2 electrons in the inner shell, 8 in the second, 14 in the third, and 3 in the valence (fourth) shell. As a Co^{2+} ion, it has lost 2 electrons from its valence shell. Thus, it has 27 - 2 = 25 electrons in total. The valence shell now has only 1 electron.

- Covalent Electrons for Molybdenum (Mo)

Molybdenum (Mo) has an atomic number of 42, which corresponds to 42 electrons in a neutral atom. The Mo atom has 2 electrons in the inner shell, 8 in the second shell, 18 in the third shell, and 14 in its fourth shell which includes valence electrons. As a Mo^{4+} ion, it has lost 4 electrons. So, it has 42 - 4 = 38 electrons in total. The valence shell now has 10 electrons.

- Covalent Electrons for Ruthenium (Ru)

Ruthenium (Ru) is in the 8th group and has an atomic number of 44, meaning a neutral atom has 44 electrons. The Ru atom has 2 electrons in the first shell, 8 in the second shell, 18 in the third shell, and 16 in its valence shell. As a Ru^{4+} ion, it has lost 4 electrons and thus has 44 - 4 = 40 electrons in total. The valence shell has 12 electrons.

- Covalent Electrons for Platinum (Pt)

Platinum (Pt) features an atomic number of 78, equating to 78 electrons for a neutral atom. The arrangement of electrons is 2 in the inner shell, 8 in the second shell, 18 in the third shell, 32 in the fourth shell, and 18 in the valence shell. As a Pt^{2+} ion, it loses 2 electrons, hence it has 78 - 2 = 76 electrons. Consequently, the valence shell contains 16 electrons.

- Covalent Electrons for Osmium (Os)

Osmium (Os) has an atomic number of 76, which means 76 electrons are present in a neutral atom. The electron distribution includes 2 in the innermost shell, 8 in the second shell, 18 in the third shell, 32 in the fourth shell, and 16 in the valence shell. In its Os^{3+} ion form, it has lost 3 electrons, giving it a total of 76 - 3 = 73 electrons. Therefore, the valence shell now has 13 electrons.

- Covalent Electrons for Vanadium (V)

Vanadium (V) with an atomic number of 23 has 23 electrons. In a neutral atom, the electrons are distributed as follows: 2 in the first shell, 8 in the second shell, 11 in the third shell which includes valence electrons. As a V^{3+} ion, it has lost 3 electrons. This results in a total of 23 - 3 = 20 electrons for the V^{3+} ion. The valence shell has 2 electrons after the loss.

Key concepts

Understanding Electronic Configuration

Electronic configuration represents the distribution of electrons in the orbitals of an atom or ion. By comprehending electronic configuration, we can predict an element's chemical properties, including reactivity and bonding behavior.

Consider the electronic configuration of cobalt (Co), which has an atomic number of 27. In its neutral form, cobalt's electrons are arranged as 1s² 2s²2p⁶ 3s²3p⁶d⁷ 4s². When Co loses two electrons to become Co²⁺, it loses them from the 4s orbital. This changes its valence shell's configuration and affects its chemical properties.

For ions, the electronic configuration details how many electrons are present after the loss or gain associated with the ion's charge, which is crucial for comprehending the ion's reactivity and interactions with other elements.

Periodic Table Groups and Valence Electrons

Elements in the periodic table are organized into groups based on their valence electron configurations, which influence the group's characteristics. For example, group 9, which includes cobalt (Co), is characterized by elements having similar electronic configurations in their outermost shell.

Metals often form cations by losing electrons from their valence shell, directly impacting their oxidation states and chemical behavior. The periodic table groups provide a visual representation to quickly determine how many electrons are in an element's outermost shell and predict the possible charges of ions they can form.

For instance, vanadium (V), from group 5, typically forms a V³⁺ ion by losing three electrons. This emphasizes the periodic table's importance in facilitating predictions about an element's potential ion charges and valence electron counts.

Oxidation States and Metal Ions

The oxidation state, often referred to as oxidation number, denotes the degree of oxidation of an atom within a compound or ion. It is crucial for understanding redox reactions, where electrons are transferred between substances.

Metal ions exhibit positive oxidation states because they tend to lose electrons. For instance, Co²⁺ indicates that cobalt has an oxidation state of +2 due to the loss of two electrons. This concept explains the valence electrons count for metal ions, as the oxidation state relates to the number of electrons lost or gained.

Understanding an element's common oxidation states can assist in determining the arrangement of electrons in metal ions after electron loss. For example, the Mo⁴⁺ ion, with an oxidation state of +4, suggests that molybdenum has parted with four of its valence electrons, altering its electronic configuration and its chemical and physical properties as a result.