How can energy levels of electrons be determined

Notice that we say probable location. Because of the electron's small size and high energy, we are limited in how precisely we can mark its position at any instant. We can only describe regions around the atom's nucleus within which the electron may be found. In describing these regions of space, we also recognize that the energy of an electron is quantized. What does this statement mean?

A property is quantized if it is available only in multiples of a set amount. If you are pouring a soft drink from a can, you can pour out as much or as little as you like. However, if you are buying a soft drink from a machine, you can buy only a certain amount. You cannot buy a half or a third of a can of soda; you can buy only a whole can or several cans. Soft drinks dispensed by a machine are available only in multiples of a set volume, or quantum. Thus, the dispensing of soft drinks by machine has been quantized.

Let's look at the simplest atom, a neutral hydrogen atom. Its energy levels are given in the diagram below. The x-axis shows the allowed energy levels of electrons in a hydrogen atom, numbered from 1 to 5. The y-axis shows each level's energy in electron volts eV. Electrons in a hydrogen atom must be in one of the allowed energy levels.

If an electron is in the first energy level, it must have exactly If it is in the second energy level, it must have An electron in a hydrogen atom cannot have -9 eV, -8 eV or any other value in between. It needs to gain The electron can gain the energy it needs by absorbing light. If the electron jumps from the second energy level down to the first energy level, it must give off some energy by emitting light.

The atom absorbs or emits light in discrete packets called photons, and each photon has a definite energy. Only a photon with an energy of exactly The energy that a photon carries depends on its wavelength. Chlorine has 17 electrons. Two is the maximum number of electrons for the level so the other electrons will have to go in higher energy levels. The electron arrangement of chlorine is 2, 8, 7. The electron arrangement also provides information about the number of valence electrons.

The valence electrons are the electrons in the highest energy level and the ones involved in ion and bond formation. Knowing the number of valence electrons will allow us to predict how a particular element will interact with other elements.

Electrons in lower energy levels are called the core electrons. Let's look at the figure below which shows the electron diagram for magnesium and its 12 electrons.

The electrons always fill the lowest energy levels available until that level is filled, then electrons fill the next energy level until it is filled. This continues for all of the electrons in an atom. It is willing to lose 2 electrons so that it has the same electron arrangements as the nearest noble gas, which is neon 2, 8.

Atoms will gain or lose electrons to look like the nearest noble gas because the noble gases are unreactive due to the stability of having eight electrons in the highest energy level. This desire of atoms to have eight electrons in their outermost shell is known as the octet rule.