ELECTRONIC CONFIGURATION PERIODICITY OF ELEMENTS

1. ELECTRONIC CONFIGURATIONPERIODICITY OF ELEMENTS

2. PERIODIC TABLE • Most powerful tool in the study of chemistry. • Order the elements by Z number. • Used to predict undiscovered elements and their properties. (Recall recent discoveries of atoms with Z = 113, 115) • Periodicity is explained by quantum mechanics.

3. From H to Multielectron Atoms • In H, AOs with the same n have the same E. • In multielectron atoms, • For a given set of QNs, orbital energies are lower than in H (larger Z value). • AOs with the same n value but different ℓ have different energies (nondegenerate). • orbitals with the same n and ℓ have the same E. • 3d and 4s have similar energies

4. DETERMINING ELECTRONIC CONFIGURATIONS • There are four quantum numbers [n, ℓ, mℓ, ms] which have defined relationships to each other • These 4 QNs are used to define a set of atomic orbitals that electrons fill. • Aufbau (building-up) Principle determines the order of filling AOs; i.e. the electronic configuration of the atom.

5. ELECTRON CONFIG. (2) • Aufbau Prin. says that electrons fill AOs to achieve the lowest energy (atom’s ground state). • Electrons fill the lower energy AOs before filling the higher energy AOs. • Pauli Exclusion Principle: Max of 2 electrons per orbital; i.e. electron spins oppose and no two electrons can have the same 4 q.n. values in an atom.

6. ELECTRON CONFIG. (2) • Hund’s Rule: When filling orbitals of identical energy, fill the empty orbitals with one electron before pairing them up; I.e. maximize number of unpaired spins. • There are exceptions: e.g. 4s fill before 3d; Cr, Cu have a single 4s electron and fully- or half-filled 3d orbitals (extra stability). • Electron configs. of cations (remove from largest n AO) and anions (add according to Aufbau Prin.)

7. ELECTRON CONFIG. (3) • electron config, orbital-filling diagram, noble gas core for [the inner electrons] + valence electrons (VE). • VEs are the outermost electrons and the most important ones in chemical bonding. • Learn electron config.s through Kr; use PT to identify VEs of atoms beyond Kr. (Fig 5.17)

8. PERIODIC LAW • Now we can see how the electronic configurations of atoms lead to periodicity of elements and form the basis for chemical and physical properties of elements. • PERIODIC LAW: When the elements are arranged according to Z, their physical and chemical properties vary periodically, regularly and predictably.

9. PERIODIC LAW (2) • Elements in the nth A-Group (Main Group) have n electrons in the valence (outermost occupied) shell. • Elements in the nth period have n as the principal QN of its valence shell.

10. PERIODIC LAW (3) • Fig 5.18 shows how the Periodic Table can be used to determine electron config. • Main Group: s- and p- block elements • Transition Group: d-block elements • Lanthanide and Actinide: f-block elements • Note filling order on p 186.

11. PERIODICITY OF ATOMIC PROPERTIES • Atomic Radius, Size (Figs 5.1, 5.19, 5.20) • lower LH corner • Ionization Energy (Figs 6.3, 6.4, 6.5; Table 6.2) Atom (g) -----> Ion+(g) + electron • upper RH corner • Electron Affinity (Fig 6.6) Atom (g) + electron -----> Ion- (g) • upper RH corner

12. PERIODICITY OF ATOMIC PROPERTIES (2) • Metallic Character • lower LH corner • Nonmetallic Character • upper RH corner

13. PERIODICITY OF ATOMIC PROPERTIES (3) • Flame colors • Oxidizing agents (Group 7A) • Reducing agents (s-block) • Acidic Oxides (upper RH corner) • Basic Oxides (lower LH corner) • Amphoteric Oxides (in between)