n - principle quantum number - determines distance from the nucleus and energy

1. n - principle quantum number - determines distance from the nucleus and energy l - orbital angular momentum quantum number l = 0, 1, 2,… n-1 ml - magnetic quantum number ml = -l, …. 0, …. +l (2l+1) values ms - spin quantum number ms = +1/2 or -1/2

2. Electron configuration - a list of all occupied orbitals of an atom, with the number of electrons that each contains H 1s1 The electronic structure of an atom determines its chemical properties In many- electron atoms, because of shielding by other electrons and different degree of “penetration” of orbitals, electrons feel an “effective” nuclear charge. Order of the energy of orbitals in a given shell is typically s < p < d < f.

3. Atom Z*(2s) Z*(2p) Li 1.28 B 2.58 2.42 C 3.22 3.14 N 3.85 3.83 O 4.49 4.45 F 5.13 5.10 Note that value of Z* increases across the period Pauli Exclusion Principle: No more than two electrons may occupy any given orbital. When two electrons occupy an orbital their spins must be paired. No two electrons in an atom can have the same set of quantum numbers

6. Subshell energies of multi-electron atoms depend on both n and l Electrons are assigned to subshells in order of increasing “n+l” value For two subshells with the same value of “n+l” electrons are assigned first to the subshell of lower n Experimentally determined order of subshell energies

7. Building Up: fill orbitals starting with the lowest energy (aufbau principle), pairing electrons as determined by the Pauli principle.

8. Using the “n+l” rule to which of the following subshells should an electron be assign first? a) 4s or 4p b) 5d or 6s c) 4f or 5s

9. n = 1, l = 0, ml= 0, ms = +1/2 or -1/2 H - one electron, occupies the 1s orbital Electron configuration: 1s1 He - two electrons, both occupy the 1s orbital with paired spins (opposite spins) Electron configuration: 1s2 He has a CLOSED shell; a shell containing the maximum number of electrons allowed by the exclusion principle n = 1, l = 0, ml= 0, ms = +1/2 n = 1, l = 0, ml= 0, ms = -1/2

10. n = 1, l = 0, ml= 0, ms = +1/2 n = 1, l = 0, ml= 0, ms = -1/2 n = 2, l = 0, ml= 0, ms = +1/2 or -1/2 Li - three electrons. Two in 1s and one is 2s Electron configuration: 1s2 2s1 Li has a “core” made up of an inner helium-like closed shell and an outer shell, valence shell, containing a higher energy electron. Can denote Li electron configuration as [He] 2s1 Electrons in the outer most shell are the valence electrons and are the ones involved in bonding and in chemical reactions.

11. If more than one orbital in a subshell is available, add electrons with parallel spins to different orbitals of that subshell rather than pairing electrons in one of the orbital -Hund’s rule

12. Closed shell unpaired electrons - paramagnetic All electrons paired: diamagnetic

13. In the presence of an external magnetic field, the electron aligns itself along the direction of the field or against the direction of the field - results in two spin states, +1/2 or -1/2 Atoms with unpaired electrons - paramagnetic - attracted to a magnet Atoms with paired electrons - diamagnetic

14. An atom of any element can be considered to have a noble gas core surrounded by electrons in the valence shell, the outermost occupied shell. The valence shell is the occupied shell with the largest n. All the atoms in a given period have a common valence shell, and the principle quantum number of that shell is equal to the period number. The valence shell of elements in Period 2 (Li to Ne) is the shell with n = 2 Atoms in the same period have the same type of core Atoms in Period 2: have a helium-like core (1s2) Period 3 atoms: Ne-like core (1s2 2s2 2p6) TABLE

15. Atoms in the same group: have analogous valence shell configurations that differ in the value of n Group I: valence configuration is ns1 Group IV: valence configuration ns2np2 TABLE

16. Use the position of element in the periodic table to determine electron configuration

18. Electron configuration of Ti Determine position of Ti on the periodic table Second member of the 3d block Electron configuration: 1s2 2s2 2p6 3s2 3p2 4s2 3d2 or [Ar] 3d2 4s2 Bi: [Xe] 4f14 5d10 6s2 6p3 TABLE

19. C: [He] 2s1 2p3 Energy DE C: [He] 2s1 2p3 Excited states- when an atom absorbs energy an electron can occupy a higher energy orbital; energy absorbed must equal to the difference in energy between the excited and ground state Ground state of C: [He] 2s2 2p2 Excited state of C: [He] 2s1 2p3

20. Periodicity of Atomic Properties Elements in the same group have the same number of valence electrons and related electron configurations; hence have similar chemical properties. The ground state electron configuration of the elements vary periodically with atomic number; all properties that depend on electron configuration tend to vary periodically with atomic number

21. The variation of effective nuclear charge through the periodic table plays an important role in determining periodic trends Zeff increases from left to right across a period, but drops every time an outer electron occupies a new shell.