Try the new Google Books
Check out the new look and enjoy easier access to your favorite features
Page 2
Try the new Google Books
Check out the new look and enjoy easier access to your favorite features
Kinetic and potential energy of atoms result from the motion of electrons. When electrons are excited they move to a higher energy orbital farther away from the atom. The further the orbital is from the nucleus, the higher the potential energy of an electron at that energy level. When the electron returns to a low energy state, it releases the potential energy in the form of kinetic energy.
kinetic potential energy atoms
Kinetic and potential energy of atoms, well you remember what kinetic energy is it's the energy of motion of movement. Potential energy is stored energy like that rock up on the ledge it's about to come crashing down and get converted into kinetic energy and you remember that energy can easily be converted from potential energy to kinetic energy and back to potential energy.Well this also applies to the atomic the atomic level to atoms so for example we've got an atom and here's the nucleus and here are some electrons going around it in their shells and if we apply some energy to that atom, energize that atom, we're going to increase the kinetic energy, what does that mean? Well the kinetic energy of the atom is really in the electrons and these electrons are going to get excited and increase their kinetic energy, the motion of the electrons and when they get excited enough energy, they can actually jump out here to an orbital further away from the center and when they jump up and getn become farther away from the center, that's potential energy that energy has now been converted to a form of energy that's stored energy. What will happen now is at some point, this excited atom will release that energy and the electron will jump back down and when it does that it will convert that potential energy back into kinetic energy and that kinetic energy might be in the form of visible light, so when you see something burning what's happening in those atoms after they get excited they're jumping back down and releasing light energy and you you've seen that in the color of the the visible light or it might be releasing it in the form of heat, so these are types of kinetic energy, energy of motion so what happens to atoms is they absorb energy, they become [IB] they become excited, excited electrons jump to higher orbitals where they store that energy and then at some point they will release that energy and convert it back into kinetic energy so this is just showing kinetic and potential energy are easily transferred even at the atomic level and we see that in atoms.
In the Bohr model of the hydrogen atom we take the potential energy of the electron to be zero at infinity, so the potential energy becomes negative as the electron approaches the hydrogen atom. However kinetic energy is always positive.
In the Bohr ground state the potential energy is -27.2 eV. Note that as described above this energy is negative. The kinetic energy is +13.6eV, so when we add the two together we get the total energy to be -13.6eV.
The total energy is negative because the electron is bound to the hydrogen atom and to remove the electron we have to put in energy. In fact we have to put in 13.6eV, which is simply the ionisation energy of hydrogen. Since the ground state has an energy of -13.6eV when we put in +13.6eV that makes the total energy zero, and as we said at the start this is the energy of the electron at infinity.
In any system where the force obeys an inverse square law there is a link between the potential and kinetic energy. This link is called the virial theorem and it says that if we call the potential energy $V$ and the kinetic energy $T$ the relationship is:
$$ V = -2T $$
Note the minus sign in this equation. The total energy $E$ is $V+T$, and if we add $T$ to both sides of this equation we get:
$$ E = V + T = -T = V/2 $$
That is why the total energy is half the potential energy.