Electrons in Atoms

Models of the Atom

5.1.1 – I can identify the inadequacies in the Rutherford atomic model I can identify the new proposal in the Bohr model of the atom I can describe the energies and positions of electrons according to the quantum mechanical model I can describe how the shapes of orbitals related to different sub-levels differ.

 Elements Elements  Rutherford’s atomic model couldn’t explain the chemical properties of elements.

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 Niels Bohr (Danish ) a student of Rutherford saw that his model needed improvement.  Bohr proposed that an electron is found only in specific circular paths, orbits, around the nucleus.  Energy levels – the fixed energies an electron can have.

 Energy levels are like steps or rungs on a ladder.  Quantum – amount of energy required to move an electron from one energy level to another energy level.  Energies between levels are not all the same

 Erwin Schrödinger (Austrian ) used math to describe the behavior of the electrons.  Quantum mechanical model – modern description of electrons in atoms based on mathematical solutions to the Schrödinger equation.

 The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.  Think of as a fuzzy cloud of chance.

 Atomic orbitals – a region of space in which there is a high probability of finding an electron.  Distinguished by n (principle quantum number or energy level) and a number (n = 1, 2, 3…)

 In each energy level there are orbitals (shapes) called sublevels.  Each energy sublevel corresponds to a different shape, which describes where the electron is likely to be found.

Atomic Orbitals video

 Each energy level has as many sublevels as the level number (ex: level 1 has 1 sublevel, level 2 has 2 sublevel (shapes).

 To find the maximum number of electrons in an energy level use 2n 2.

1s orbital = 1 total orbital 2s orbital 2p orbitals 3s orbital 3p orbitals 3d orbitals 4 total orbitals 9 total orbitals

Electron Arrangement in Atoms

I can describe how to write the electron configuration for an atom I can explain why the actual electron configurations for some elements differ from those predicted by the aufbau principle.

 Electron configuration – way in which electrons are arranged in atoms.  Three rules – the aufbau principle, the Pauli exclusion principle, and Hund’s rule – tell you how to find the electron configuration.

 Aufbau principle – states that electrons occupy the orbitals of lowest energy first.  Orbitals on any sublevel are always the same energy.

 Pauli exclusion principle – an atomic orbital may describe at most two electrons.  When electrons pair they must have opposite “spins” so they don’t repel as much.

 Hund’s rule – electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.  Basically singles in a sublevel until they have to double up.

 Shorthand for these are: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 …

 Some actual electron configurations differ from those assigned using the aufbau principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations.