Getting from the orbitals to the elements All elements have the same set Atomic number dictates how many are filled – how many electrons are added Filling orbitals follows a fixed pattern: lowest energy ones first Questions: What is the order of the energies? And how many electrons per orbital?

Orbital energy levels and order of filling

Electrons share orbitals (only two allowed) – a consequence of spin

Capacities of the sublevels – 2 x number of orbitals Number of members Electron capacity 1s, 2s etc 1 2 2p, 3p etc 3 6 3d, 4d etc 5 10 4f, 5f etc 7 14

Add electrons to the orbitals – lowest first 2p 3d 3p 4p 4s 3s 2s 1s H(z = 1)

Fill lowest orbital 2p 3d 3p 4p 4s 3s 2s 1s He(z = 2)

Begin next orbital 2p 3d 3p 4p 4s 3s 2s 1s Li(z = 3)

Fill 2s 2p 3d 3p 4p 4s 3s 2s 1s Be(z = 4)

Begin filling 2p 2p 3d 3p 4p 4s 3s 2s 1s B(z = 5)

Electrons don’t like to pair C(z = 6)

2p 3d 3p 4p 4s 3s 2s 1s N(z = 7)

2p 3d 3p 4p 4s 3s 2s 1s O(z = 8)

2p 3d 3p 4p 4s 3s 2s 1s F(z = 9)

Filled 2p – neon (unreactive) 4s 3s 2s 1s Ne(z = 10)

4s is lower in energy than 3d Next electron enters 4s not 3d 2p 3d 3p 4p 4s 3s 2s 1s K(z = 19)

But 3d is lower in energy than 4p Next electron enters 3d not 4p 2p 3d 3p 4p 4s 3s 2s 1s Sc(z = 21)

Follow the red brick road: fill orbitals in correct order Practice makes perfect

Electronic configurations Provides a complete description of all electrons in atom according to orbital occupancy Consider Al: atomic number 13 Has thirteen electrons Orbitals occupied in order: 1s22s22p63s23p1 Occupancy “Sublevel” quantum number Principal quantum number

Abbreviated configurations For large elements, the full configuration becomes unwieldy Substitute the largest noble gas for all the filled rows, but not the unfilled rows Na is 1s22s22p63s1 Ne is 1s22s22p6 Na is [Ne]3s1 Leads into concept of valence and core electrons

Shells The orbitals with the same Principal Quantum number (1,2,3 etc) are grouped into shells (levels) Filled shells have special significance Filled shell 1 Filled shell 1 Unfilled shell 2 Filled shell 2

Shells A shell (level) contains all the orbitals with the same principal quantum number Filling shell corresponds to filling entire period in table (2, 8 or 18 electrons) Filled shells are in the core – they do not participate in the chemistry

# of valence electrons = group number The electrons in the unfilled shell are called the valence electrons This unfilled shell is the valence shell The valence electrons are involved in bonding For any element: # of valence electrons = group number Quantum number of shell (n) = period number

Shape of the periodic table explained by orbital picture 6 groups 2 groups 10 groups 14 groups