2 Niels Bohr created 1st model of the atom Want to explain excited atoms & and the line-emission spectrumBut TOO simpleStill useful however!Helped us to develop the current model of electron activity – the “quantum model”
3 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 orbitalThen 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 !
4 The Bohr Model More orbitals = more energy states! Big jumps = Bigger Energy!Small jumps = smaller energy (lower freq)Remember E=hνCan determine the relative energy levels of the orbitals by looking at the energies of the photons emitted
5 Good & Bad about the Bohr Model Great for explaining the line-emission spectrum of hydrogenNot great for everything! More complex atoms don’t work! New model needed!Was right about the line-emission spectra & using it to see electron configurationsBIG PROBLEM! Electrons don’t orbit like planetsModern model developed, called the “quantum model of the atom”
7 The Quantum Model of the Atom Electrons don’t go around like planets -- found in cloudsClouds are called “orbitals”Electron movement is random but it has to stay in its own orbitalExcited electrons jumping between orbitals = light emittedOrbitals are described by their shape, the energy level they are on, and their orientation.
8 Orbital Shapes Four types of orbitals Shapes: Called the “s”, “p”, “d” and “f”.Nucleus is at the center of each orbitalEach orbital can hold a maximum of two electronsShapes:s orbitals = spherical cloudsp orbitals = figure eight cloudsMost d orbitals = cloverleaf cloudsF orbitals are very complicated and we won’t be drawing them= electronVideo of Orbitals
9 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 nucleus1s orbital is a spherical cloud close to the nucleus7s orbital is a spherical cloud far from the nucleus.Not all types of orbitals exist at each energy levelNucleus1s cloud7s cloud“1s” electrons“7s” electrons
10 Orbital Orientations S orbitals - one orientation At each energy level only 1 s orbitalP-orbitals -3 orientationsP orbitals =figure eightsCan fit 3 around the nucleus1 horizontally (the “x orientation”)1 vertically (the “y orientation”)1 that goes in & out (the “z orientation”)D- orbitals- 5 orientationsF orbitals- 7 orientations
11 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”.
12 Putting it all together How does an electron “live”Can talk about:Energy LevelShapeOrientationSpinFor examplelives in the “3Py” orbital and spins uplives in the “3Px” orbital and spins downnucleus
13 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?1Oxygen?8Carbon?6Sodium?11