| Valence Electron |
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Determining the number of valence electrons To determine the quantity of valence electrons an element has, one must look at the family (vertical column) in which the element is categorized. With the exception of groups 3–12 ( Transition Metal s), the number within the unit's place identifies how many valence electrons are contained within the elements listed under that particular column.
Valence electrons in chemical reactions The chemical behavior of atoms is largely due to interactions between electrons. Electrons of an atom remain within certain, predictable Electron Configurations . Electrons fall into Shell s based on their relative energy level which is usually visualized as their mean distance from the nucleus. The valence electrons have the greatest influence on chemical behavior. Core electrons (those not in the outer shell) play a role, but it is usually in terms of a secondary effect due to screening of the positive charge in the atomic nucleus. Wavefunction s of Hydrogen . The Principal Quantum Number is at the right of each row and the Azimuthal Quantum Number is denoted by letter at top of each column.]] Each shell, numbered from the one closest to the nucleus (lowest in energy), can hold up to a specific number of electrons due to its differing sublevel and orbital capacity: To determine the electron capacity of a shell, the formula 2''n''² is used, where ''n'' is the shell number or principal quantum number. Electrons fill orbitals and shells from the inside out, beginning with shell one. Whichever occupied shell is currently most outward is the valence shell, even if it only has one electron. The reason why shells fill up in order is that the Energy Level s of electrons in the innermost shells are significantly lower than the energy levels of electrons in outer shells. So if the inner shells were not completely full, the electron in an outer shell would quickly "fall" into the inner shell (with the emission of a Photon that would carry away the difference in the energy). The number of electrons in an atom's outermost valence shell governs its bonding behavior. Therefore, elements with the same number of valence electrons are grouped together in the Periodic Table of the elements. As a general rule, the fewer electrons in an atom's valence shell, the more Reactive it is. Group 1 metals are therefore very reactive, with Caesium , Rubidium , and Francium being the most reactive of all metals. Every atom is much more stable, or less reactive, with a full valence shell. This can be achieved one of two ways: an atom can either share electrons with neighboring atoms, a Covalent Bond , or it can remove electrons from other atoms, an Ionic Bond . Another form of ionic bonding involves an atom giving some of its electrons to another atom; this also works because it can end up with a full valence by giving up its entire outer shell. By moving electrons, the two atoms become linked. This is known as Chemical Bond ing and serves to build atoms into Molecule s or ionic compounds. Five major types of bonds exist:
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