Chemistry of S-Block Elements Mrs.Vaishali Mahajan PERIODIC CLASSIFICATION OF ELEMENTS 1) Main Group Elements : These are the elements in group 1,2,13 to 17 2) Noble or inert gas elements: Group 18 elements 3) Transition elements : Elements in Group 3 to 12 4) Inner transition elements : Lanthanides and Actinides Elements BLOCKS IN PERIDIC TABLE 1) S-block Elements : Elements of group 1 & group 2 2) P-block Elements : Elements of Group 13 to 17 3) d- block Elements : These elements placed between s & p block elements. 4) f-block Elements : This block is placed at the bottom of the periodic table. ATOMIC RADIUS The bonding atomic radius is defined as one- half of the distance between covalently bonded nuclei. SIZE Bonding atomic radius tends to… …decrease from left to right across a row due to increasing Zeff. …increase from top to bottom of a column due to increasing value of n IONIZATION ENERGY • = amount energy required to remove a valence electron from an atom in gas phase • 1st ionization energy = energy required to remove the most loosely held valence electron (e- farthest from nucleus) •Cs valence electron lot farther away from nucleus than Li •electrostatic attraction much weaker so easier to steal electron away from Cs •THEREFORE, Li has a higher Ionization energy then Cs ELECTRONEGATIVITY ability of atom to attract electrons in bond noble gases tend not to form bonds, so don’t have electronegativity values Unit = Pauling Fluorine: most electronegative element = 4.0 Paulings Decreased Electronegativity Decreased Ionization Energy (easier to remove an electron) Increasing Atomic Radius Increased Ionization Energy (harder to remove an electron) Increased remove to Ionization Energy (harder Increased Increased Electronegativity QUANTUM NUMBER Each atomic orbital in an atom is characterized by a unique set of three quantum numbers (from Schrödinger’s wave equation) n, l, and ml Principal quantum number (n) - designates size of the orbital Integer values: 1,2,3, and so forth The larger the “n” value, the greater the average distance from the nucleus Correspond to quantum numbers in Bohr’s model Angular momentum quantum number (l) - describes the shape of the atomic orbital Integer values: 0 to n 1 0 = s sublevel; 1 = p; 2 = d; 3 = f Magnetic quantum number (ml) - describes the orientation of the orbital in space (think in terms of x, y and z axes) Integer values: l to 0 to + l Electron spin quantum number (ms) - describes the spin of an electron that occupies a particular orbital Values: +1/2 or 1/2 Electrons will spin opposite each other in the same orbital Pauli Exclusion Principle - no two electrons in an atom can have the same four quantum numbers; no more than two electrons per orbital Aufbau Principle - electrons fill according to orbital energies (lowest to highest) Hund’s Rule - the most stable arrangement for electrons in orbitals of equal energy (degenerate) is where the number of electrons with the same spin is maximized ORDER IN WHICH ORBITALS ARE FILLED SHAPES” OF ATOMIC ORBITALS : 1) “s” orbital - spherical in shape 2) “p” orbitals - two lobes on opposite sides of the nucleus 3) “d” orbitals - more variations of lobes (double dumbell) 4) “f” orbitals - complex shapes SHAPES” OF ATOMIC ORBITALS :.