Valence electrons are the electrons found in the outer most energy level of an atom that are attracted most loosely. The number of valence electrons an atom has determines the types of chemical bonds that it is likely to take part in.
Each element has between 1 and 8 valence electrons. Most atoms are less likely to react if they contain 8 valence electrons. Electron dot diagrams are used to express the number of valence electrons an element has. When different elements form chemical bonds, electrons can either be shared or transferred from one atom to another.
Valence electrons can be estimated by using a periodic table. The number of valence electrons increases from left to right across a period. Each element has just one more valence electron than the element to its left on the periodic table. This image displays the number of valence electrons in the elements in period 2 and 3 on the periodic table.