welcome to the bohr atomic model in which we will take a look at how light energy and electron
energy led niels bohr to proposing his planetary model of the atom let's see what born knew back in
1913 that allowed him to develop his model of the atom first there is the electromagnetic spectrum
we can look at this spectrum as wavelengths of light that have a very wide range
from greater than 100 meters to less than a trillionth of a meter a narrow band within
that range are light waves that our brains can detect through our eyes absorbing those energies
and so this is the visible spectrum with each color corresponding to a different wavelength
other wavelengths correspond to a variety of different waves such as radio waves microwaves
infrared ultraviolet x-rays and gamma rays and these are simply names given to different ranges
of wavelengths and as the wavelengths get shorter the energy of the wave gets bigger
bohr knew that one electrons have energy two light has energy and three energized elements
emit various colors of light that are unique to each element or in other words each element has
its own unique signature of colors but no one knew why bohr figured out the why and that is what this
video is about how did he do that let's look at the element that bohr first looked at hydrogen if
we energize hydrogen gas with an electric current hydrogen emits a color spectrum of four colors
our nervous system however is not able to see the four individual colors
our brain integrates those four colors into one specific color so that's the color we see but
when we diffract or split hydrogen's pale pinkish color we can then see the colors that are actually
being emitted by hydrogen atoms violet at 411 nanometers blue at 434 nanometers a blue green
at 486 nanometers and red at 656 nanometers this is the emission spectrum of hydrogen
an emission spectrum is all the specific colors emitted by an energized substance
in 1913 using the atom's vast empty space provided by rutherford's nuclear model of the atom
nielsborg created a model of the atom that explained the behavior of electrons in the atom
and explained the existence of the emitted colors in bohr's atomic model the electrons orbit the
nucleus the electrons can only have specific discrete energies and the higher their allowed
energy the larger the radius of their orbit in bohr's model for an electron transitioning from
higher to lower energy from a further orbit to a closer orbit the difference in energy is emitted
as light a larger difference in the change of the electron energy results in higher energy light
the energy of the emitted light is equal to the electrons energy change and those different light
energies give us different colors of light notice that in the transition the electron does not exist
in between those allowed energies the electron can only exist at discrete allowed energies
if the electron could exist at any energy then there would be any amount of change in
electron energy which would result in emitting a large spectrum of colors a continuous rainbow
but only specific colors are seen and those specific colors are constant and so the electron
changes are constant and so the electron exists at specific discrete energies the orbits are numbered
with integers which has important mathematical significance in bohr's analysis and representing
the electron's energy bohr found that these energies result in hydrogen's emission spectrum
and electrons energy change from n equals three to n equals two emits the energy
of red light an electron's energy change from n equals four to n equals two emits the energy
of blue green light and from five to two gives blue light without being disturbed
the electron exists at the lowest energy possible which is called the ground state
if a ground state electron absorbs the right amount of energy it can go to a higher energy but
will then lose that energy in the form of light and go back to ground state the electron that
has absorbed energy is called an excited state electron so ground state absorbs energy goes to
excited state loses energy and goes back to ground state ground state electron excited state electron
and ground state electron the amazing thing is that bohr's model was able to account for the
emission spectra of all the other elements and so it became a very powerful model from which to
build the current model of the atom the quantum mechanical model in summary electrons orbit the
nucleus at specific energies the higher the electron energy the further its orbit is from
the nucleus three electrons will remain at the lowest possible energy the ground state unless
they absorb a specific amount of energy that will allow them to get to a higher allowed energy
called the excited state which is a larger orbit for if an electron absorbs energy it will then
lose that energy in the form of light energy which we see as specific colors when diffracted
bohr's model was an essential step toward developing the quantum mechanical model
of the atom over the following 13 years which is our current model of the atom
see ya