The Bohr Model

Niels Bohr created 1st model of the atom Want to explain excited atoms & and the line-emission spectrum But TOO simple Still useful however! Helped us to develop the current model of electron activity – the “quantum model”

The Bohr Model Thought electrons orbited like planets Thought that when an atom is “excited”, they jump up into higher orbits “what goes up, must come down” Come down– they lose energy and ??? Excited electron absorbs heat (gains energy)and jumps up to a higher-level orbital Then the electron falls back to a lower level orbital . Since energy can’t disappear, the energy lost by the electron as it falls down is released as light. Photon of light is emitted – this is what we see as the color of the burning element !

The Bohr Model More orbitals = more energy states! Big jumps = Bigger Energy! Small jumps = smaller energy (lower freq) Remember E=hν Can determine the relative energy levels of the orbitals by looking at the energies of the photons emitted

Good & Bad about the Bohr Model Great for explaining the line-emission spectrum of hydrogen Not great for everything! More complex atoms don’t work! New model needed! Was right about the line-emission spectra & using it to see electron configurations BIG PROBLEM! Electrons don’t orbit like planets Modern model developed, called the “quantum model of the atom”

Students Being the "Bohr" The Atom Song

The Quantum Model of the Atom Electrons don’t go around like planets -- found in clouds Clouds are called “orbitals” Electron movement is random but it has to stay in its own orbital Excited electrons jumping between orbitals = light emitted Orbitals are described by their shape, the energy level they are on, and their orientation.

Orbital Shapes Four types of orbitals Shapes: Called the “s”, “p”, “d” and “f”. Nucleus is at the center of each orbital Each orbital can hold a maximum of two electrons Shapes: s orbitals = spherical clouds p orbitals = figure eight clouds Most d orbitals = cloverleaf clouds F orbitals are very complicated and we won’t be drawing them = electron Video of Orbitals

Orbital Energy Levels Orbitals exist on different energy levels 7 possible energy levels: 1,2,3,4,5,6, and 7. Higher energy levels = farther from the nucleus 1s orbital is a spherical cloud close to the nucleus 7s orbital is a spherical cloud far from the nucleus. Not all types of orbitals exist at each energy level Nucleus 1s cloud 7s cloud “1s” electrons “7s” electrons

Orbital Orientations S orbitals - one orientation At each energy level only 1 s orbital P-orbitals -3 orientations P orbitals =figure eights Can fit 3 around the nucleus 1 horizontally (the “x orientation”) 1 vertically (the “y orientation”) 1 that goes in & out (the “z orientation”) D- orbitals- 5 orientations F orbitals- 7 orientations

Electron “Spin” 2 electrons can be in each orbital i.e. the 3s orbital holds two electrons, the 4Px orbital holds two, the 4Py orbital holds two, etc. In the same orbital – Electrons have opposite magnetic “spins” one spins “up” and the other spins “down”.

Putting it all together How does an electron “live” Can talk about: Energy Level Shape Orientation Spin For example lives in the “3Py” orbital and spins up lives in the “3Px” orbital and spins down nucleus

The Final Information: So how many electrons does a particular atom have, and which orbitals are they found in? # of electrons in an uncharged atom = # of protons (remember?) which orbitals the electrons are found in - will take a bit longer to answer. Time to learn about the “Atom’s Family!” So how many electrons does a hydrogen atom have? 1 Oxygen? 8 Carbon? 6 Sodium? 11