ELECTRONIC CONFIGURATION PERIODICITY OF ELEMENTS

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.

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

DETERMINING ELECTRONIC CONFIGURATIONS There are four quantum numbers [n, ℓ, m ℓ, m s ] 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.

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.

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.)

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)

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.

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.

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.

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

PERIODICITY OF ATOMIC PROPERTIES (2) Metallic Character –lower LH corner Nonmetallic Character –upper RH corner

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)