Electron Configuration

1. Electron Configuration Atoms and how their electrons orbit inside them!

2. Quick Note! • An electron exists and moves in an orbital • An orbital has a certain shapeand 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

3. Quantum Numbers • Quantum numbers describe the behavior of an atom’s electrons

4. 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 = n2

5. Angular Momentum Quantum Number l • lrepresents 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

7. 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

8. 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

9. Quantum Numbers

10. 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

12. Electron Configuration • Three RULES! • 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? Energy 2py 2px 2pz 2s 1s

13. Electron Configuration • Three RULES! • 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? Energy 2py 2px 2pz 2s 1s

14. Electron Configuration • Three RULES! • 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? Energy 2py 2px 2pz 2s 1s

15. 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 togetherex: put all p orbitals of one level closer together

16. Orbital Notation • Orbital notation is a visual notation using arrows to represent electrons and lines to represent orbitals • H ___ He ___ B ___ ___ ___ ___ ___ 1s 1s1s 2s 2p

17. Electron-Configuration Notation • Electron-Configuration Notations uses the principle quantum number, the orbital letter, and the number of electrons in superscript • H = 1s1 He = 1s2 B = 1s22s22p1

18. 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 = 1s22s22p63s13p64s2 that is really long! • Ca is close to Ar; Ar = 1s22s22p63s13p6 • Therefore: Ca = [Ar]4s2

19. 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