An atom can be at its lowest energy state, ground state, or gain energy to move to excited states, higher energy levels, in discrete steps.
The electrons in an atom tend to be arranged in such a way that the energy of the atom is as low as possible, also known as the ground state.
When those atoms are given energy, the electrons absorb the energy and move to a higher energy level. These energy levels of the electrons in atoms are quantized, meaning again that the electron must move from one energy level to another in discrete steps rather than continuously. An excited state of an atom is a state where its potential energy is higher than the ground state.
A photon is a source of energy that electrons can absorb to make a quantum jump to a higher energy level: when the energy (E = hf) of the photon is equal to the energy difference between the discrete steps.
An atom in the excited state is not stable. When it returns to the ground state, it releases the energy that it had previously gained in the form of electromagnetic radiation. The electron can reach its ground state level either with one direct jump or with shorter jumps via intermediate levels. If an excited electron emits a photon, the energy hf of that photon equals the energy difference between the initial energy level of the electron and a lower level. By measuring the photons emitted the size of these energy levels can be determined.
This can be seen in electron configurations when the configuration of an electron is out of sync with the general N+1 rule. For example, the electron configuration 1s22s23p5 has no excitation as it follows the expected pattern but the configuration 1s22s23p43d1 shows an electron has jumped up to the 3d orbital.
Practice Questions
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Key Points
• Energy levels of the electrons in atoms are quantized, meaning again that the electron must move from one energy level to another in discrete steps.
• An atom changes from the ground state to excited states when it absorbs or releases energy.
Key Terms
Ground state: is the lowest energy state of the atom.
Excited-state: of an atom is a state where its potential energy is higher than the ground state
Photon: the smallest discrete amount of electromagnetic radiation. It is the basic unit of all light, carrying the energy E= hf.