The sum of the masses of protons, neutrons, and electrons in an atom or group of atoms is called atomic mass. molecule into the atomic weight Automic mass so over here to into vapour density will be equal to 2 because two atoms makeup one molecule of chlorine into 35.5 which is given as the atomic weight of chlorine so these two will cancel on both sides giving a vapour density 35. It happens roughly a quarter of the time in nature. There are 17 protons and 20 neutrons in the universe. Because both isotopes of chlorine have 17 positive protons in the nucleus and 17 negative protons from electrons in the surrounding orbitals, it doesn’t matter which isotope is present in a chemical reaction.Ĭonsider a chlorine atom, which has 17 protons and has two isotopes: chlorine 35 and chlorine 37. Relative atomic mass = ( 75 100 35) + ( 25 100 37) =35.5īecause neutrons have no charge, all isotopes of any element act chemically the same. The atomic weight, or relative atomic mass, is a weighted average of the weights of all chlorine isotopes. When the mass of chlorine is determined with a mass spectrometer, the result is 35.5. That means there is 75 percent Chlorine-35 and 25% Chlorine-37 in any pure chlorine mixture that can be isolated from all other elements.
Chlorine-37 has 17 protons and 20 neutrons and is found about 25% of the time in nature. Chlorine comes in two forms: chlorine-35 and chlorine-37.Ĭhlorine-35, which has 17 protons and 18 neutrons, is found in nature roughly 75% of the time. Isotopes are atoms that have the same number of protons (17 in the case of chlorine) but variable numbers of neutrons. Why is the atomic mass of chlorine taken as 35.5 u and not a whole number like 35 u or 36 u explain?īecause of something called isotopes, chlorine has an atomic weight of 35.5 instead of 35.
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