Bohr Model Electron Orbital 101

An introduction The Bohr Model of the atom and its electrons was developed after Rutherford had developed the concept of the nucleus and with electrons around. But how the electrons moved around was a puzzle. Standard models didn’t work. From what we know of physics, the electron should collapse into the nucleus But some clues came from another puzzle, how light rays (photons) strike, are absorbed and emitted from atoms.

Introduction, cont. Photons, light rays, are packets of pure energy. They packets that act light waves: Light waves can have a high frequency: Or a low frequency: The frequency is equal to the amount of energy in the light: –E = h ( where E is energy, h is a constant, and is the frequency) –Violet and Blue are high frequency, red and orange are low frequency and energy

Introduction, cont. It had been discovered that atom could, if conditions were right, absorb or give off photons of very exact frequencies. If an atom absorbed one particular color of blue, it could also, when heated, emit that exact color of blue. This gave Bohr the idea that electrons could be orbiting the atom with only certain exact levels of energy

Bohr Model Beginning That atoms have protons and electrons That protons are in the center and electrons outside That the electrons “orbit” around the nucleus at a certain distance and momentum. They are attracted to the nucleus, but don’t fall in - Protons Electrons Atom +

Bohr Proposed: The electron’s “orbit” has a certain level of energy. Electrons can only exist in fixed levels Electrons can “jump” from one energy level to another, and so change the amount of energy they have - + Level 1 Level 2 Level 3 Level 4

Level 1 Level 2 The Reason Electrons Change Orbits Electrons normally are found in the lowest possible orbit Atoms can receive energy from the outside, such as from a photon. After a period of time, the electron will “shed” its energy by releasing another photon. The added energy will boost the electron’s orbit Incoming Photon Exiting Photon

Bohr Model and Energy Each orbital has a specific amount of energy ( E 1, E 2, E 3,E 4. etc.). The higher and larger the level, the more the energy E1E1 E2E2 E3E3 E4E4

Energy and Changes in Orbital For an electron to move up a level, it must absorb a photon The photon’s energy equals the energy needed to get to a higher level E1E1 E2E2 Energy of added photon

Energy and Changes in Orbital The energy needed equals the difference between the two levels. E 2 – E 1 = E photon And the energy of the photon is related to the frequency E photon = h E1E1 E2E2 {

E1E1 E2E2 E3E3 E4E4 Photons of different energy ( and frequency) can raise the electrons to higher levels Low Energy Photon Medium Energy Photon High Energy Photon Very High Energy Photon

Energy levels of Electrons Electrons can gain energy in specific amounts They can also lose energy in specific amounts E5E5 E4E4 E3E3 E2E2 E1E1

Energy levels of Electrons The electrons don’t need to start in level 1. They can begin in level 2 Or level 3, etc. E5E5 E4E4 E3E3 E2E2 E1E1

Energy levels of Electrons And they can lose the same amounts of energy, each time releasing a photon of that energy E5E5 E4E4 E3E3 E2E2 E1E1

Energy levels of Electrons If the atom receives a very large amount of energy, the electron could be completely knocked out of orbit. That is what happens when an atom is ionized E1E1 E4E4 E2E2 E3E3 E5E5 E3E3 E4E4 E2E2 E1E1 E infinity