The number of electrons in an element's outermost shell, also known as its valence electrons, is determined by its position in the periodic table. The periodic table is organized based on the atomic number of elements, which corresponds to the number of protons in an atom's nucleus.
The valence electrons of an element are the electrons located in the highest energy level or shell of an atom. The maximum number of electrons that can occupy a particular shell can be determined using the 2n^2 formula, where "n" represents the shell number. For example, the first shell (n = 1) can hold a maximum of 2 electrons, the second shell (n = 2) can hold a maximum of 8 electrons, and so on.
The outermost shell of an atom is called the valence shell, and the number of electrons in this shell determines the element's valence. Elements in the same group or column of the periodic table typically have the same number of valence electrons. For instance, elements in Group 1 (such as hydrogen and lithium) have 1 valence electron, elements in Group 2 (such as beryllium and magnesium) have 2 valence electrons, elements in Group 13 (such as boron and aluminum) have 3 valence electrons, and so on.
The valence electrons are important because they are involved in the chemical bonding behavior of elements. Elements with the same number of valence electrons tend to exhibit similar chemical properties and can form similar types of chemical bonds.