TCA: Chemistry M'sOnline version All about the M's by Elvira Trevino 1 109: Meitnerium: 276 2 115: Moscovium: 288 3 101: Mendelevium: 258 4 12: Magnesium: 24.305 5 25: Manganese: 54.938 6 42: molybdenum: 95.96