Problem 49 - Chemistry A Molecular Approach

Question

Determine the number of valence electrons in an atom of each element. a. Ba b. Cs C. \(\mathrm{Ni}\) d. S

Step-by-Step Solution

Answer

Ba has 2 valence electrons, Cs has 1 valence electron, Ni has 10 valence electrons, and S has 6 valence electrons.

Step 1 - Valence Electrons of Ba

Barium (Ba) belongs to Group 2 of the periodic table, which means it has 2 valence electrons.

Step 2 - Valence Electrons of Cs

Cesium (Cs) is in Group 1 of the periodic table, so it has 1 valence electron.

Step 3 - Valence Electrons of Ni

Nickel (Ni) is a transition metal, and its valence electrons can be a little more complex to determine. Ni has an electron configuration of [Ar]4s2 3d8. Generally, for transition metals, the valence electrons are the electrons in the outermost s and d orbitals. Nickel has 10 valence electrons (2 from the 4s orbital and 8 from the 3d orbitals).

Step 4 - Valence Electrons of S

Sulfur (S) is in Group 16 of the periodic table, which means it has 6 valence electrons.

Key Concepts

Periodic Table Groups

Understanding the organization of the periodic table is essential when studying chemistry, particularly when finding the number of valence electrons in an element. The periodic table is divided into rows called periods and columns called groups. Elements in the same group often share similar properties, including the number of valence electrons. These outermost electrons are crucial as they determine how an element will react chemically.

For instance, Group 1 elements, except for hydrogen, are known as alkali metals and have one valence electron, making them highly reactive. Group 2 elements, called alkaline earth metals, have two valence electrons. Moving across to Group 16, elements like sulfur have six valence electrons, often participating in chemical bonds by gaining or sharing two electrons to achieve a stable configuration. Group 17 elements are halogens with seven valence electrons and are just one electron shy of a full octet, making them very reactive as well. Lastly, noble gases in Group 18 have complete electron shells, which is why they are historically known as inert or non-reactive.

To help students grasp this more easily, visualize each group as a 'family' with members holding a specific number of 'tickets' (valence electrons) which they use to engage in 'activities' (chemical reactions).

Transition Metals

Transition metals are located in the central block of the periodic table, specifically groups 3 through 12. They're characterized by their ability to possess valence electrons in more than one shell, namely, the outermost s and nearby d orbitals. This configuration endows transition metals with unique properties such as variable oxidation states and the capability to form colored compounds.

Take nickel (Ni) for an example. It has an electron configuration of [Ar]4s2 3d8, implying that its valence electrons are the two in the 4s orbital and the eight in the 3d orbitals, adding up to ten. Not all transition metals follow a strict rule for determining valence electrons because of their complex electron configurations. As learners approach these elements, envision them as multifaceted individuals with diverse skills (electronic configurations), which they use depending on the scenario (chemical reaction or bonding situation).

For transition metals, the relatively low energy difference between the s and d orbitals allows electrons to reside with relative ease in both, making these metals versatile and essential in various applications, from industrial to biological.

Electron Configuration

Electron configuration describes the distribution of electrons of an atom or molecule in atomic or molecular orbitals. It's the roadmap to understanding an element's reactivity and bonding behavior. Knowing the electron configuration allows chemists to determine the valence electrons, which are involved in forming bonds.

The most stable electron configuration is one that fills or half-fills an energy level and is achieved by following the Pauli Exclusion Principle, Hund's Rule, and the Aufbau Principle. For most elements, determining the valence electrons is relatively straightforward once you know their electron configuration. For example, sulfur has an electron configuration of [Ne]3s2 3p4, indicating it has a total of six valence electrons — two from the 3s and four from the 3p orbitals.

However, exceptions occur with some transition metals and other elements where electron configurations may not follow a predictable pattern. Yet, understanding the basic principle that electrons fill from lower to higher energy levels provides a solid foundation for students to grasp more complex configurations.