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Understanding the concept of valence electrons is critical when it comes to predicting chemical properties and bonding behavior of elements. Valence electrons are the electrons in the outermost shell, or energy level, of an atom. They are the electrons involved in forming bonds with other atoms. For example, sodium (Na), with an atomic number of 11, has its outermost electron configuration as 3s1, indicating one valence electron in the third shell.

Valence electrons play a pivotal role in determining how an atom will interact with others. Atoms with a complete set of valence electrons, typically mimicking the noble gases with full outer shells, exhibit a stable arrangement and are less likely to react chemically. This fundamental understanding provides the basis for exploring why atoms gain or lose electrons.

Electron loss occurs when an atom sheds electrons in order to achieve a more stable electron configuration, often during the process of forming ions. This phenomenon is known as oxidation. Atoms that lose electrons become positively charged ions or cations. The number of electrons that an atom loses can be predicted by its valence electrons.

For instance, sodium (Na), which has one valence electron, tends to lose that electron to assume a stable electron configuration similar to neon. By losing an electron, the sodium atom achieves a noble gas configuration and becomes a Na+ ion. This electron loss is a key concept in understanding the reactivity and bonding of different elements, especially metals.

A stable electron configuration is often associated with the electron arrangement of noble gases, which have full valence shells and are not inclined to gain or lose electrons. Other elements strive to achieve this state of stability by gaining, losing, or sharing electrons to complete their valence shells.

Atoms will often lose or gain electrons to reach eight electrons in their valence shell, a state referred to as the 'octet rule', which is indicative of chemical inertness or stability. The process of reaching this stable state drives chemical reactions, and it helps predict an atom's tendency to form chemical bonds. For example, magnesium (Mg), which has two valence electrons, will tend to lose both to achieve a state akin to neon, while aluminum (Al), with three valence electrons, will lose all three to resemble the electron configuration of neon.

The atomic number is a fundamental feature of an element and is equivalent to the number of protons in the nucleus of an atom. This number also determines the unique electron configuration of the atom and subsequently its place in the periodic table. The atomic number is crucial for identifying the number of protons and electrons an atom has when it is electrically neutral.

For example, sodium (Na) has an atomic number of 11, which means it possesses 11 protons and, when neutral, 11 electrons. This number helps in deducing that sodium will have one electron in its outermost shell—the valence electron to lose for achieving stability.

Atoms reach a noble gas configuration when they have full valence electron shells, resulting in exceptional stability and inertness. The noble gases—helium, neon, argon, krypton, xenon, and radon—are the natural embodiers of this rule due to their filled outermost electron shells.

Elements are driven by a chemical incentive to emulate the electron configuration of noble gases; this stability criterion often directs the chemical behavior of an element. To illustrate, after losing one, two, or three electrons, sodium (Na), magnesium (Mg), and aluminum (Al) respectively, each achieves a noble gas configuration that explains their tendency to lose a specific number of electrons, corresponding with their number of valence electrons.