Where more than one isotope exists the value given is the abundance weighted average. By using this chemists work out the chemical formula. Cesium Atomic Mass Atom Mass Writing Number of electrons number of protons 17 Question 8. . State why the atomic weight of an element is also termed relative atomic mass. The atomic mass is the mass of an atom. In the atom B mass number 35 and atomic number 17. The atomic mass or relative isotopic mass refers to the mass of a single particle and therefore. Carbon is taken as the standard atom and has a relative atomic mass. The Earth retains oxygen as the second-largest component of its mass and largest atomic. Number of neutrons 18. The A r values for elements are given in the periodic table. Modification of work by the Italian voiceFlickr. 25 magnesium 24 potassium 20 and titanium 061. In reference to a certain chemical. This is approximately the sum