Photoelectric effect – When EM strikes the surface of certain metals causing ejection of electrons Requires a minimum frequency threshold (0) The number of electrons ejected depends on the intensity of the incident radiation EK of the ejected electrons depends on frequency

Balmer Series

Niels Bohr’s Atomic Model Electrons ‘orbit’ the nucleus, but at fixed energies. Based on the energetic properties of electrons, there are a fixed set of allowed ‘orbits’ – called “stationary states”. If it stays in one state, the E for an electron does not change. If an electron passes from one state to another, its E changes (up or down) by emitting or absorbing photons.

EXAMPLE: If we know that the electron of a hydrogen atom has a speed of 2.05 x 106 m/s. If we know the precision of this value to be 1.5%, with what precision can we measure the position of the electron at a given instant of time?

The 3 Primary Quantum Numbers Principle quantum number; ‘n’ (1,2,3,…) defines ‘shell’ describes energy* and extent of orbital an orbital of quantum number ‘n’ has n-1 nodes Angular momentum (azimuthal) quantum number; ‘l’ (0 – n-1) defines ‘subshell’ l=0 ‘s’; l=1 ‘p’; l=2 ‘d’; l=3 ‘f’; describes shape of orbital Magnetic quantum number; ‘ml’ (-l – +l) describes orientation of orbital represents quantization of angular momentum

The s-Orbitals

The p-Orbitals

Definitions In a given shell of a multi-electron atom, orbital energies increase with increasing ‘l’ Orbitals of a given subshell have the same energy and are therefore degenerate Each orbital can hold 2 electrons with different ‘spin’ According to the Pauli exclusion principle, no two electrons in a given atom can have the same set of 4 quantum numbers According to Hund’s rule, the lowest energy arrangement of electrons in degenerate orbitals is when like spin is maximized Aufbau, German for ‘build up’: the method to assign electron configurations in the ground state