Question

What is the value of \(n\) for the valence shells of (a) Al, (b) Se, (c) \(\mathrm{Ba},\) and (d) \(\mathrm{Sb}\) ?

Short answer

The values of n for the valence shells are: (a) Al: 3, (b) Se: 4, (c) Ba: 6, and (d) Sb: 5.

Step-by-step solution

Understanding Valence Shells

The valence shell is the outermost shell of an atom where the valence electrons are located. The valence electrons are responsible for the chemical properties of the element. The period number in the periodic table represents the value of the principal quantum number, n, which corresponds to the number of the valence shell.

Identifying the Period for Aluminum (Al)

To find the valence shell of Al, look at its position in the periodic table. Aluminum is located in the 3rd period. This indicates that its valence electrons are in the 3rd shell. Therefore, for Al, the value of n is 3.

Identifying the Period for Selenium (Se)

Selenium is in the 4th period of the periodic table. This means that its valence electrons are in the 4th shell. Thus, for Se, the value of n is 4.

Identifying the Period for Barium (Ba)

Barium is located in the 6th period of the periodic table. Hence, the valence electrons of Ba are in the 6th shell, and the value of n is 6 for Ba.

Identifying the Period for Antimony (Sb)

Antimony is placed in the 5th period in the periodic table. Consequently, the valence electrons for Sb are in the 5th shell, indicating that the value of n for Sb is 5.

Key concepts

Understanding the Periodic Table

The periodic table is a systematic arrangement of the chemical elements, ordered by their atomic number, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number, which is the number of protons in an atom's nucleus.

At its core, the periodic table is divided into periods (horizontal rows) and groups (vertical columns). Elements in the same period have the same number of atomic orbitals. For instance, every element in the first period has electrons in one orbital, while every element in the second period has electrons in two orbitals, and so on. This feature directly relates to the principal quantum number, as the period number indicates the number of the outermost shell, where the valence electrons are found.

Furthermore, each group contains elements with similar chemical properties, because they have the same number of valence electrons. For example, group 1 elements (alkali metals) all have one electron in their outer shell, leading to similar reactivity patterns. By understanding the periodic table's structure, students can more easily predict and understand how different elements will interact with each other.

Principal Quantum Number and Atomic Structure

The principal quantum number, symbolized by n, is an integer that denotes the energy level and size of the electron orbital. It plays a key role in the structure of an atom and determines the distance of an electron from the nucleus.

The principal quantum number starts at 1 and increases as you move outward from the nucleus. A higher value of n indicates the electron resides in a shell farther away from the nucleus, typically with higher energy levels. The periodic table essentially maps these quantum numbers, wherein each period corresponds to a principal quantum number and hence the energy level of an atom's valence electrons.

The valence shell is the outermost populated shell, given by the principal quantum number, and it is especially important because it holds the electrons that are most likely to be involved in bonding and chemical reactions. This relationship between the periodic table and the principal quantum number allows chemists to rationalize the arrangement of the elements and predict their chemical behavior. An understanding of the principal quantum number also aids students in grasping why elements in the same period share certain attributes.

Chemical Properties and Their Relation with Valence Electrons

Chemical properties of an element are greatly influenced by its valence electrons—those electrons that are located in the outermost shell of an atom. These are the electrons involved in forming chemical bonds with other atoms.

Chemical reactivity is primarily determined by the number of valence electrons. Atoms with a complete set of valence electrons, typically noble gases with eight valence electrons, are generally inert because they are energetically stable. On the other hand, elements with just one valence electron, such as sodium, are highly reactive since they can easily lose that one electron to achieve a stable configuration.

Moreover, atoms tend to gain, lose, or share electrons to complete their outer shell and reach a stable electronic configuration, usually resembling the nearest noble gas. This pursuit of stability is the driving force behind the formation of chemical bonds and compounds. By analyzing an element's position on the periodic table, students can deduce its number of valence electrons and predict how it might engage in chemical reactions, making the periodic table a critical tool for understanding chemical properties.