After the third energy level has 8 electrons, the next electron goes into the fourth level. 4th Period: Potassium and Calcium—Electrons go into the fourth energy level. A small piece of sodium metal ...

They include lithium, sodium and potassium, and are placed in the first vertical column on the left of the periodic table. All the Group 1 elements are very reactive, and all react with water to ...

Our bodies require other elements, including non-metal elements such as phosphorus (P), sulphur (S) and chlorine (Cl), and metal elements like potassium ... of the periodic table and are mainly ...