Write orbital diagrams for the valence electrons and indicate the number of unpaired electrons for each element. (a) \(\mathrm{Br}\) (b) \(\mathrm{Kr}\) (c) \(\mathrm{Na}\) (d) In

Valence electrons are the electrons situated in the outermost shell of an atom, which is also referred to as the valence shell. These electrons play a pivotal role in the chemical properties of elements, including how they bond with other atoms. The valence shell is defined by the highest energy level, represented by the principal quantum number, denoted as 'n'.

For instance, in the case of Bromine (Br), with an electron configuration of [Ar]3d¹⁰4s²4p⁵, its valence electrons would be located in the 4s and 4p orbitals because they are the outermost occupied shells. Knowing the distribution of these electrons helps us understand an element's reactivity, as they are the ones involved in forming chemical bonds.

It's important for students to grasp that while the inner electrons also contribute to the overall stability of atoms, it's the valence electrons that dictate most of the typical chemical reactions and are frequently represented in diagrams to illustrate bonding scenarios.

Unpaired electrons refer to electrons in an atom's orbitals that do not have a corresponding electron with opposite spin. These electrons are significant because they can contribute to the magnetic properties of an element and are often available for chemical bonding. In orbital diagrams, which are pictorial descriptions of the electrons in an atom's orbitals, unpaired electrons are denoted by single arrows.

As demonstrated in the example with Sodium (Na), with an electron configuration of [Ne]3s¹, we observe that there is only one electron in the 3s orbital, making it unpaired. This unpaired electron is crucial for the chemical reactivity of Sodium, as it tends to lose this electron to achieve a more stable electron configuration, indicative of its propensity to participate in ionic bonding.

Understanding unpaired electrons is essential for predicting the behavior of atoms in different chemical contexts, especially in oxidation-reduction reactions where these electrons are transferred between atoms.

Electron configuration is the arrangement of electrons in an atom's orbitals. It is depicted using the principal energy levels and subshells, represented by quantum numbers and letters, respectively. The electron configuration can be thought of as a map that shows where the electrons reside in an atom. It is crucial for predicting an element's chemical behavior, as the arrangement of electrons influences the types of bonds that an element can form.

For each of the examples provided in the exercise, the electron configurations are distinct. Indium (In), for example, with an electron configuration of [Kr]4d¹⁰5s²5p¹, indicates that the electrons occupy up to the fifth energy level. The 'd' and 's' orbitals are filled according to the Aufbau principle, which states that electrons fill orbitals starting with the lowest available energy states.

A solid comprehension of electron configuration is not only foundational for constructing orbital diagrams but also for understanding the periodic trends and the quantum mechanical nature of atoms. It serves as a baseline for more advanced topics in chemistry such as molecular orbital theory and spectroscopy.