Types of calculationsFinding atomic mass, given mass and abundance of eachFinding the mass of one of the isotope given atomic mass and abundance.Finding abundance given atomic mass and mass of eachNOTE if atomic mass is not given for 2 and 3 above use the mass in the periodic table. How do we deal with the fact that some atoms have several isotopes?The solution is to measure the mass of each individual isotope in the element and then calculate the weighted average.The weighted average is known as the atomic mass of the element
For carbon: Mass = 12.0199% 12C AND 1% 13C found in nature12.01 = average mass based on abundance NOT just 12Ītomic Massis the weighted average mass of all the naturally occurring isotopes of that element. IsotopesDo isotopes have similar chemical properties? Why? Yes electrons are the sameDo they have similar physical properties? Why? NO mass is different.Remember:Isotopes have:same # of protonsdifferent # of neutronsĪtomic Mass Unit is a unit used to compare the masses of atomsand has the symbol u or amu.ġ amu or u is approximately equal to the mass of a single proton or neutron.Ĭarbon-12Chemists have defined the carbon-12 atom as having a mass of 12 atomic mass units. IsotopesThey have different mass numbers because they have different numbers of neutrons, but they have the same atomic number because they have the same number of protons.Atoms of the same element with Same number of protons Same number of electrons Different number of neutrons Other ways to write elements:3617ClCl-36Atomic NumberMass NumberMass Number Mass Number (A):The sum of the protons and neutrons in the nucleus. How many electrons does sodium have?111111 # p+ =# e- The atomic number of an element also equals the number of electrons in a neutral atom of that element Z =#e-Įx: SodiumWhat is the atomic number of Sodium? Z=#p+ The number of protons (atomic number) determine the identity of an element.Ītoms have no overall electrical charge (neutral) so, an atom must have as many electrons as there are protons in its nucleus. Is the number of protons in the nucleus of the atom. Atomic Number, Mass Number, Atomic Mass and Isotopes