Atomic energies-how to determine?

[sangria1986]

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Ok so I know electrons need energy added to them to be removed. So when an electron is removed does this mean the atoms energy decreases? Does the energy added then go to the electron not the atom? How about when adding an electron? Affinity rules indicate that energy is released for the more electronegative atoms when an electron is added. And less energy released by the more metallic ones. Am I thinking too much into this?

Also how to calculate mass defect? Is that basically the energy released to make an atom from it's parts?
Electron +proton mass- natural state atoms mass = energy released to make atom which is equal to mc^2? Thus this value is always negative because energy is released?

 

[Rabolisk]

Don't get too wrapped in the signs of these values. When an electron is removed, it means that the energy of the system (atom + electron) increases. You're breaking the "bond" between the atom and the electron, which requires energy. Electron affinity is energy released when an atom gains an electron. Some textbooks report this as a negative value, because energy of the system decreases, and the process is exothermic. Some just report it as a positive value, assuming implicitly that the process is exothermic. That's why you'll hear that electron affinity INCREASES from left to right, although if you counted it as negative, it would DECREASE. Just know that fluorine is likely to gain an electron, whereas group I metals are not.

You're correct as far as mass defect goes. This value is generally reported as positive, although you just need to know that energy is released when a nucleus forms from its constituent nucleons. The reason nuclear fusions and nuclear fission work is because iron has the greatest mass defect per nucleon.