Valence electrons are the outermost electrons in an atom. They are located in the valence shell, which is the outermost energy level or electron shell of an atom. The valence shell is also referred to as the electron cloud or electron cloud region.The number of valence electrons in an atom determines its chemical properties and reactivity. Atoms with the same number of valence electrons will have similar chemical properties and will tend to react in similar ways. For example, atoms with one valence electron, such as hydrogen and lithium, are highly reactive, while atoms with eight valence electrons, such as neon and argon, are relatively unreactive.Valence electrons are involved in chemical reactions, such as bonding and chemical reactions. In chemical reactions, valence electrons are either transferred or shared between atoms. The transfer of valence electrons is known as ionic bonding, while the sharing of valence electrons is known as covalent bonding.In order to determine the number of valence electrons in an atom, the periodic table of elements can be used. The periodic table is arranged in order of increasing atomic number, and the number of valence electrons is indicated by the group or column in which the element appears. Elements in group 1, for example, have one valence electron, while elements in group 8 have eight valence electrons.It's worth noting that the electron configuration of an atom can be also determined by the number of electrons in the energy level and their distribution among the subshells (s,p,d,f) and the order of filling by Aufbau principle. Therefore, it can be used to predict the chemical properties of an atom and its reactivity.In summary, valence electrons are the outermost electrons in an atom, located in the valence shell. Their number determines the chemical properties and reactivity of an atom. They are involved in chemical reactions, such as bonding and chemical reactions, and can be determined by using the periodic table of elements or by determining the electron configuration of an atom.