Valence electrons is the name given to the outermost electrons of any given element. Every element has from one to eight valence electrons and they determine how the element will combine in chemical reactions with other elements. When elements react with other elements in ionic reactions they will generally gain or lose electrons to minimize the number of electrons moving from one element to the other.
Metals - those elements to the left of the stairstep elements on the periodic table - generally have 1-3 valence electrons while non-metals generally have 5-7 valence electrons. This explains why, when metals react with non-metals that the metals lose their valence electrons to become positive cations while the non-metals gain valence electrons to become negative anions. This is called the octet rule and says all elements are most stable when they have a full number of valence electrons. For all but a handful of elements that number is eight - hence the "octet" rule.
In the periodic table the elements are arranged in groups or families based on the number of valence electrons the element has because that number identifies elements with similar properties.
The octet rule also explains why the group 18 elements (the noble gases) do not react. Since they already have a full outer shell of electrons, it takes a large amount of energy to remove one of their valence electrons and would add a large amount of energy of one more valence electron was added.
Valence electrons are the outermost electrons in an atom. Thus, they require less energy to remove than electrons at lower energy levels (if any). Also, they are the electrons that neighboring atoms will interact with. Hence, the valence electrons are the most important electrons in determining how an atom will react chemically with other atoms.
The number of valence electrons is the metric that organizes the periodic table. Since atoms with the same number of valence electrons share chemical properties, columns of elements in the periodic table have the same valence number.
Atoms with a complete shell of valence electrons tend to be chemically inert, while atoms with only one or two valence electrons (or valence holes) are highly reactive, since they easily lose or gain electrons to achive the more stable condition of a full valence shell.
the valence electron(s) are the one(s) which an atom gains or loses or shares during the chemical reaction.
An element gains or loses electrons according to:1- being metal so it loses electrons (like the sodium atom which has 1 electron in the outer shell , magnesium atom which has 2 electrons in the outer shell) 2- being non-metal so it gains electrons (like flourine atom which has 7 electrons in the outer shell , nitrogen which has 5 electrons in the outer shell) 3- being inert gas (but these type of atoms don't share in chemical reactions under ordinary conditions)
Metals always tend to lose their valency electron(s) and these electrons in the outer level (shell) vary from : 1 to 3 electrons so it's easier for the matals to lose them because gaining 5,6 or 7 electrons will be harder .
Non-metals always tend to gain or share electrons ,,,,, gain electrons in ionic bonds : NaCl where sodium loses an electron and gives it to a chlorine atom so Cl puts in its outer level. The non-metals share electrons in covalent bonds which arises between 2 non-metals : like : nitrogen + nitrogen= nitrogen molecule where each nitrogen atom shares by 3 electrons with the other nitrogen and they form one nitrogen molecule together ,,,,,
Why do elements share, lose or gain their valency electrons? in order to be in a stabled state and each atom has 8 electrons in its outer level and that's why the inert gases don't enter chemical reactions since they already have outer levels completely filled with electrons.