Identify all of the phases in your answer. A rgon is a chemical element with symbol Ar and atomic number 18. A measure of the stiffness of a substance. Menu; atomic number list. Holmium is a part of the lanthanide series, holmium is a rare-earth element. The chemical symbol for Holmium is Ho . 44 protons/electrons. Atomic mass of Holmium is 164.9303 u. It is in group 18 of the periodic table and is a noble gas. An atomic mass unit ($$\text{amu}$$) is defined as one-twelfth of the mass of a carbon-12 atom. The excess neutrons act somewhat like nuclear glue.Â Only two stable nuclides have fewer neutrons than protons: hydrogen-1 and helium-3. We are all familiar with the lighter-than-air gas helium, but whenever I see a balloon floating on a string, I feel a little sad. Astatine is the rarest naturally occurring element on the Earth’s crust. Periodic table starts at top left ( Atomic number 1) and ends at bottom right (atomic number 118). 147,178,968 stock photos online. The melting point of Holmium … Holmium is a chemical element with atomic number 67 which means there are 67 protons and 67 electrons in the atomic structure. An element is a substance made from one or more atoms of the same atomic number. Both are written before the chemical symbol, with the mass number written as a superscript and the atomic number written as a subscript. • They are moving very fast in a volume surrounding the nucleus. Arsenic is a metalloid.