C L A U D I A B E R N E D O

Electronic Structure

Ground State vs. Excited States

  Electrons are normally in their ground   When they absorb energy, they get promoted to

excited states.   Excited states are higher in energy than ground

states.   Excited states come back down to the ground state

via release of energy.

Quantum Numbers

  Electron address   Principal quantum number ‘n’: designates which

shell the electron   Sublevel ‘l’: designates subshell (s,p,d,f) l: n-1   Magnetic quantum number ‘ml’: designates precise

orbital of the subshell. –l to +l   Spin + or -

Geometric Shapes

Rules

  Heisenberg Uncertainty Principle: The more we know about the momentum of any particle, the less we know about the position.

  Pauli Exclusion Principle: no two electrons in same atom can have same four quantum numbers.

  Aufbau Principle: shells and subshells of lower energy gets filled first

  Hund’s Rule: electrons will not fill any orbital in the same subshell until all orbitals in that subshell contain at least 1 electron

Bohr atom

  Electron orbiting the nucleus in a circular orbit.   Larger n values have larger orbiting radii.

Effective nuclear Charge

  Effective nuclear charge = nuclear charge - shielding electrons.   Shielding electrons are those that stand between the nucleus and the

electron we are interested in.   Shielding electrons are those that are in subshells closer to the

nucleus (lower in energy) than the electron we are interested in.   MCAT questions usually give you a diagram of the Bohr model, in

which case, shielding electrons are those that orbits at a smaller radius.

  The higher the effective nuclear charge for an electron, the more stable it is (higher ionization energy, not easily knocked off).

  Effective nuclear charge increases for outer electrons as you go across (left to right) the periodic table.

Questions

1.  Which of the following is the correct electron configuration for the bromide ion, Br-?

a)  [Ar] 4s24p5

b)  [Ar] 4s23d104p5

c)  [Ar] 4s23d104p6

d)  [Ar] 4s23d104p65s1

e)  [Ar] 4s23d103p6

Questions

1.  Which orbital cannot exist? a)2p b)3p c)4d d)3f