The chemical formula for chlorophyll "d" is C54H70MgO6N4. This means that a single molecule of this substance contains 54 atoms of carbon, 70 atoms of hydrogen, 6 atoms of oxygen, and 4 atoms of nitrogen. And, also, that "Mg" symbol in the middle of the chemical formula stands for "Magnesium." Since it is in the middle for this chemical formula, this means that it is known as the central magnesium atom. I hope that this has helped find the answer that you were looking for. Enjoy your day, and take care.