Lecture 1 Complete: s, p Block Elements PDF

s,p block elements Dr. Sarah Nagy 1  The periodic table Is the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. Consists of 7 horizontal periods...

s,p block elements Dr. Sarah Nagy 1  The periodic table Is the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. Consists of 7 horizontal periods, with the lanthanides and the actinides (f-block elements) kept separately below and 18 vertical groups. The periods are of varying lengths. Period number Number of elements in each period 1st (the hydrogen period) 2 elements 2nd, 3rd each has 8 elements 4th, 5th each has 18 elements 6th, 7th each has 32 elements The periodic table is classified into blocks (s,p,d,f blocks). A block of the periodic table is a set of elements unified by the orbitals where their valence electrons lie in. 2 s- block consists of 2 groups IA , II A p- block consists of 6 groups III A, IVA, VA, VIA, VIIA , 0 (noble gases) d- block (transition metals) consists of 10 groups III B, IV B, VB, VIB, VIIB , VIIIB, IB, IIB f- block consists of 14 groups 3 4 Quantum numbers To completely describe an electron (its location and energy) in an atom, four quantum numbers are needed: principle (n), orbital angular momentum (ℓ), magnetic (mℓ), and spin (ms) quantum numbers. https://www.youtube.com/watch?app=desktop&v=Aoi4j8es4gQ Watch the video carefully 1) Principle quantum number (n) It represents the principle energy level of the electron. It can have positive integer value. n= 1, 2, 3,…. The higher the n value the further the electron from the nucleus K- shell L- shell M- shell 5 2) The orbital angular momentum quantum number (ℓ) Describes the shape of the orbital (orbital: is a region of probability where an electron can be found) ℓ = 0,1,2,……..(n-1) If n=1 ℓ = 0 then we are describing s- orbital (1s) has a spherical shape If n=2 ℓ =0 , 1 s- orbital p- orbital (2s) (2p) 6 3) The magnetic quantum number (mℓ) Determines how many orbitals of a type per energy level and their orientation. mℓ = - ℓ,…. 0, …..ℓ If ℓ= 0 (i.e., s- orbital) mℓ = 0 ( it has one value which means only one s-orbital exists per energy level) S If ℓ= 2 (i.e., d- orbital) mℓ = -2,-1,0,1,2 ( it has 5 values which means if the principle energy level contains orbitals of d- type it will have 5 per energy level) dxy dyz dxz dx2-y2 dz2 7 4) The spin quantum number (ms) Describes the orientation of the electron around itself ms = + ½ or –½ clockwise anticlockwise 8  It is impossible for two electrons in an atom to have the same values of the four quantum numbers “Pauli exclusion principle”. Even if two electrons share the same orbital and hence have the same n, ℓ, mℓ quantum numbers, they will vary in the ms quantum number. Each orbital can be occupied by up to 2 electrons According to the Hund’s rule, electrons always enter an empty orbital before they pair up. Aufbau principle (building-up principle) states that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. 9 1s