Electron Configuration Atoms and how their electrons orbit inside them!

Quick Note!  An electron exists and moves in an orbital  An orbital has a certain shape and distance from the nucleus  An orbital can only hold a maximum of 2 electrons  The more electrons an atom has, the more orbitals an atom has to hold all the electrons

Quantum Numbers  Quantum numbers describe the behavior of an atom’s electrons

Quantum Numbers  “n” represents the main energy level an electron occupies  The bigger “n” gets, the further away from the nucleus the electron gets  If more than 1 electron has the same value for “n” they are in the same “shell”  “n” can only be in integer values; n≥1  The # of orbitals in a shell = n 2

Angular Momentum Quantum Number l  l represents the shape (or sublevel) of the orbital  The value for l is an integer greater than or equal to 0  l = n – 1  Each number value corresponds to a shape Value for lOrbital lettershape 0sSphere 1pDumbbell 2dButterfly 3fComplex

Magnetic Quantum Number m  m represents the orientation of the orbital about the nucleus  The values for m can be -l, 0, +l  The amount of m values correspond to the number of orientations of that shape Value for m # orbitals of that shape Orbital lettershape 01sSphere -1, 0, 13pDumbbell -2, -1, 0, 1, 25dButterfly -3, -2, -1, 0, 1, 2, 37fComplex

Spin Quantum Number  Negative repulses negative, therefore, electrons don’t like each other  Electrons want to always move in opposite directions if they have to share an orbital  Spin quantum number can be + 1 / 2 or - 1 / 2

Quantum Numbers

Electron Configuration  The arrangement of electrons in an atom  Each element has a unique electron configuration  An element will have the orbitals of the elements preceding it plus any additional orbitals to account for it’s extra electrons  Ex:  He has a level 1 s orbital,  Li has both a level 1 s orbital and a level 2 s orbital

Electron Configuration  Three RULES! 1.Aufbau principle: an electron occupies the lowest- energy orbital available If we have 5 electrons, how can we fit them so the lowest energy orbitals fill first? 1s 2s 2px 2py 2pz Energy

Electron Configuration  Three RULES! 2.Pauli Exclusion Principle: no two electrons of one atom can have the same set of 4 quantum numbers If we have 4 electrons, but they only fill 2 energy levels, how can we arrange them so they are different? 1s 2s 2px 2py 2pz Energy

Electron Configuration  Three RULES! 3.Hund’s Rule: orbitals of equal energy all fill with one electron before a second electron may be added. If we have 7 electrons, how can we fill the orbitals by energy level? 1s 2s 2px 2py 2pz Energy

Electron Configuration  Hints!  Find the number of electrons  List all orbitals available to element  Arrange orbitals from lowest to highest energy from left to right  Group like orbitals together ex: put all p orbitals of one level closer together

Orbital Notation  Orbital notation is a visual notation using arrows to represent electrons and lines to represent orbitals  H ___ He ___ B ___ ___ ___ ___ ___ 1s 1s 1s 2s 2p

Electron-Configuration Notation  Electron-Configuration Notations uses the principle quantum number, the orbital letter, and the number of electrons in superscript  H = 1s 1 He = 1s 2 B = 1s 2 2s 2 2p 1

Nobel Gas Notation  Nobel Gas Notation is a short cut notation  We know a Nobel gas will have all the orbitals up to that Nobel gas entirely filled  Therefore, we can write a Nobel Gas plus any new orbitals corresponding to the new element  Ca = 1s 2 2s 2 2p 6 3s 1 3p 6 4s 2 that is really long!  Ca is close to Ar; Ar = 1s 2 2s 2 2p 6 3s 1 3p 6  Therefore: Ca = [Ar]4s 2

Valence Electrons & Inner Electrons  Every element has a set of valence electrons. For the s and p block, there are 8 valence electrons  Electrons in the valence shell are typically in the highest occupied energy level  For Argon (1s2 2s2 2p6 3s2 3p6) this is 3  For Berylium (1s2 2s2) this is 2  All non-valence electrons are inner-shell electrons  If we know an electron configuration of a neutral atom, we can figure out which element it is