I was reading my science textbook and they have introduced the concepts of atomic mass,relative atomic mass and mass number.Here are some doubts I have- 1)Is atomic mass a ratio ? 2)1/12th of a C-12 atom is half a proton,half a neutron and half an electron.Since mass of an electron is negligible and since 1 proton=1 neutron,1/12th of a C-12 atom is basically the mass of one proton or one neutron.A hydrogen atom has 1 proton so why didn't they take 1u = mass of 1 hydrogen atom? 3)Also,if 1u = mass of a proton = mass of a neutron aren't mass number and atomic mass the exact same thing ? 4)In my book the atomic mass of Chlorine is given as 35.5.How can an atom have half a neutron or proton ? 5)Can someone please explain what relative atomic mass is along with an example as in my book just the definition is given and I couldn't understand a thing.