pls exlain briefly the chemical principles of AAS. What is it and how does it work?
My teacher has explained it a number of times but I still dont get it
Electrons in atoms are arranged in shells. To move an electron from one shell to a outer shell, you need to input a specific amount of energy (exactly X joules, anything just under or over it will not work), since it takes energy to pull an electron away from the positively charged nucleus.
Different elements have different distances between their shells. This is because every element has a different nuclear charge (eg. sodium has a nuclear charge of +11), which tends to pull all the electrons towards the nucleus. Also, different elements have a different electron configuration (eg. sodium has a 2, 8, 2 configuration). The more electrons on the outer shell, the further from the nucleus the shell tends to go, because the electrons repel one another.
If different elements have different distances between their shells, the energy required to move electrons from one shell to a higher shell will be different for different elements. Hence, different elements can absorb only specific energies.
In AAS, the energy is delivered as a light, which is basically a bunch of photons (light particles). Each photon has an energy, which is proportional to its frequency (E = hv, where E = energy, v = frequency and h is a constant). Different elements therefore absorb different specific frequencies of light - which is how one can differentiate between elements in AAS.