← Periodic table Humphry Davy 1778–1829 United Kingdom chemist Linked elements 3 Lithium (Li) 5 Boron (B) 11 Sodium (Na) 12 Magnesium (Mg) 17 Chlorine (Cl) 19 Potassium (K) 20 Calcium (Ca) 38 Strontium (Sr) 56 Barium (Ba)