Predict the number of valence clectrons present for cach of the following ions: (a) \(\mathrm{Sb}^{3+}\); (b) \(\mathrm{Rh}^{+}\); (c) \(\mathrm{Co}^{2+}\); (d) \(\mathrm{Ru}^{3+}\).

The periodic table is a master key unlocking the secrets of chemical behavior and atomic structure. It is organized into rows called periods and columns known as groups or families. Each element is placed based on its atomic number — the number of protons in its nucleus. Elements in the same group typically have similar properties and share the same number of valence electrons, which are the electrons in the outermost shell that are involved in forming bonds.
Elements in Group 1 have one valence electron, whereas Group 18 elements, the noble gases, have a full octet, except for helium which has two. The transition metals, found in the center of the table, have a less clear-cut valence electron configuration, which can lead to various ion charges. The table also guides us in understanding trends such as electronegativity, atomic radius, and reactivity, which are all pivotal when predicting how an element will behave in chemical reactions.

Electron configuration informs us about the distribution of electrons in an atom's orbitals. Valence electrons are determined based on the electron configuration, occupying the highest energy levels. For many elements, especially those on the main group, the number of electrons in the outermost shell corresponds to the group number.
In the excercise we see transition metals like Rhodium and Ruthenium. These metals, along with others in the d-block, can have multiple valence electrons due to the involvement of their d orbitals. Understanding electron configuration is crucial for predicting how an atom will interact with others, how many bonds it can form, and whether it is likely to give up or gain electrons to achieve a stable electron configuration similar to that of the nearest noble gas.

Ion charge is indicative of an element's electrical state and has a direct impact on the count of valence electrons. Ions are atoms or molecules that have lost or gained electrons, becoming charged particles. Cations are positively charged ions created when atoms lose electrons, thus reducing the number of valence electrons. Anions, on the other hand, are negatively charged ions formed by the gain of electrons, increasing their valence electron count.
In the context of our exercise, we highlighted changes in valence electrons due to the formation of ions; for example, Sb normally has 5 valence electrons but as Sb3+, it loses 3 electrons resulting in just 2 valence electrons. This concept is essential for understanding ionic compounds and predicting their formulas based on the need to balance positive and negative charges.

Chemical principles are the basic rules and concepts that underlie chemical reactions and compounds. They include understanding how valence electrons dictate an element’s chemical properties and reactivity. One of these principles lies in the octet rule, where atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons similar to noble gases, which are the most stable due to their complete valence shells.
Moreover, in a chemical reaction, the reactants undergo a transformation to become products. The conservation of mass principle stipulates that atoms are neither created nor destroyed in a chemical reaction; rather, they are rearranged. Our exercise involves predicting valence electrons after an element forms an ion, specifically how the change in electrons affects the ion’s ability to engage in chemical reactions. According to these principles, the creation of Sb3+ or Co2+ ions implies these atoms' readiness to bond and form new substances.