\(2.6\) Give the number of valence electrons for each of the following elements: (a) As; (b) \(\mathrm{V}_{\text {; (c) } \mathrm{Cl} \text {; (d) } \mathrm{Ba} \text {. }\)

In understanding valence electrons, it is crucial to comprehend how the periodic table is organized into groups. These groups, also known as families, are columns that categorize the chemical elements with common properties. Each group has a specific number that helps determine the number of valence electrons in an element. For instance, elements in Group 1 have one valence electron, while those in Group 2 have two.

When we move to Groups 13 through 18, the number of valence electrons can be more easily determined by subtracting 10 from the group number. This pattern explains why arsenic (As), found in Group 15, has 5 valence electrons, while chlorine (Cl), in Group 17, has 7. Understanding this concept is fundamental in predicting how elements will react chemically, as it is the valence electrons that are involved in forming bonds.

Electron configuration refers to the arrangement of electrons around the nucleus of an atom. It describes the orbitals that electrons occupy, and the order in which these orbitals are filled follows specific rules known as Hund's rule, the Pauli exclusion principle, and the Aufbau principle. For example, vanadium (V), which is in the Group 5 of the periodic table, has an electron configuration that ends in 3d³ 4s², indicating that its five valence electrons are in the third energy level (3d orbitals) and fourth energy level (4s orbitals).

Knowing the electron configuration is not just for categorizing elements, but also for understanding the chemical reactivity and properties of the element. Valence electrons are the outermost electrons and the ones involved in chemical bonding; thus, correct electron configuration is crucial for determining valence electrons and, consequentially, predicting bond formations.

Chemical elements are pure substances consisting only of atoms with the same number of protons in their nuclei. The valence electrons are of particular interest as they dictate an element's chemical properties and how it interacts with other elements. Barium (Ba), for example, is an element in Group 2 of the periodic table. This determines that it has two valence electrons which are in the outermost shell and participate in chemical bonding.

Different elements can have the same number of valence electrons, as seen in the exercise solution where both arsenic (As) and vanadium (V) have 5 valence electrons despite being from different groups (15 and 5 respectively). What makes each element unique is its atomic structure, which can be represented by the electron configuration. Familiarity with the concept of valence electrons across different elements can empower us to comprehend their behavior in chemical reactions and enhance our understanding of material properties.