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Atomic Structure From Indivisible to Quantum Mechanical Model of the Atom V.Montgomery & R.Smith 1 Quantum mechanical model(Modern Atomic Theory) SchrÖdinger Heisenberg Pauli Hund V.Montgomery & R.Smith 2 Heisenberg’s Uncertainty Principle Impossible to determine both the position and the velocity of an e- in an atom simultaneously with great certainty. V.Montgomery & R.Smith 3 SchrÖdinger e- not in neat orbits, but exist in regions called orbitals V.Montgomery & R.Smith 4 Definitions Orbital region in space where the probability of finding an electron is the highest V.Montgomery & R.Smith 5 Quantum Numbers Definition: specify the properties of atomic orbitals and the properties of electrons in orbitals There are four quantum numbers V.Montgomery & R.Smith 6 Quantum Numbers (1) Principal Quantum Number, n V.Montgomery & R.Smith 7 Quantum Numbers Principal Quantum Number, n Values of n = 1,2,3,… Positive integers only! Indicates the main energy level occupied by the electron V.Montgomery & R.Smith 8 Quantum Numbers Principal Quantum Number, n Values of n = 1,2,3,… Describes the energy level, orbital size V.Montgomery & R.Smith 9 Quantum Numbers Principal Quantum Number, n Values of n = 1,2,3,… Describes the energy level, orbital size As n increases, orbital size increases. V.Montgomery & R.Smith 10 Principle Quantum Number More than one e- can have the same n value These e- are said to be in the same eshell The total number of orbitals that exist in a given shell = n2 V.Montgomery & R.Smith 11 Orbital Shapes For a specific main energy level, the number of sublevels possible is equal to n. Ex. n=2, can have two sublevels. A sublevel is assigned a letter: s , p , d, f , g, h V.Montgomery & R.Smith 12 Energy Level and Orbitals n=1, n=2, n=3, n=4, only s orbitals s and p orbitals s, p, and d orbitals s,p,d and f orbitals V.Montgomery & R.Smith 13 Atomic Orbitals Atomic Orbitals are designated by the principal quantum number followed by letter of their subshell Ex. 1s = s orbital in 1st main energy level Ex. 4d = d sublevel in 4th main energy level V.Montgomery & R.Smith 14 The area where an electron can be found, the orbital, is defined mathematically, but we can see it as a specific shape in 3-dimensional space… Orbital Shapes s is spherical. One possible orientation. V.Montgomery & R.Smith 16 z y x z y The 3 axes represent 3-dimensional space x z y For this presentation, the nucleus of the atom is at the center of the three axes. x The 1s orbital is a sphere, centered around the nucleus The 2s orbital is also a sphere. The 2s electrons have a higher energy than the 1s electrons. Therefore, the 2s electrons are generally more distant from the nucleus, making the 2s orbital larger than the 1s orbital. 1s orbital 2s orbital Orbital Shapes p orbital. “dumbbell” shape V.Montgomery & R.Smith 27 There are three p orbitals 3 possible orientations The three 2p orbitals are oriented perpendicular to each other DEGENERATE ORBITALS All three orbitals are identical of each other by energy, size and shape.The only difference is their orientation in space. z This is one 2p orbital (2py) y x z another 2p orbital (2px) y x z the third 2p orbital (2pz) y x z The three 2p orbitals, 2px, 2py, 2pz y x 3p, 4p, 5p, etc… have the same shape and number, just larger Orbital Shapes d orbital. “double dumbbell” or four-leaf clover It has 5 degenerate orbitals 5 possible orientations The 4d orbitals etc…are the same shape, only larger V.Montgomery & R.Smith 34 Orbital Shapes f orbital It has 7 degenerate orbitals 7 possible orientations V.Montgomery & R.Smith 35 V.Montgomery & R.Smith 36 Energy Level and Orbitals n=1, n=2, n=3, n=4, only s sublevel s and p sublevels s, p, and d sublevels s,p,d and f sublevels V.Montgomery & R.Smith 37 In the same energy level, energies of orbitals: s<p<d<f (because of the amount of repulsion between electrons) V.Montgomery & R.Smith 38 Quantum Numbers (4) Electron Spin Quantum Number, ms = +1/2, 1/2) V.Montgomery & R.Smith 39 V.Montgomery & R.Smith 40 Electron Spin QN 1. Relates to the spin states of the electrons. 2. Electrons are –1 charged and are spinning 3. The two possible spin directions are called +½ and –½ Pauli Exclusion Principle Wolfgang Pauli No 2 e- in an atom can have the same set of four quantum numbers (n, l, ml, ms ). Therefore, no atomic orbital can contain more than 2 e-. and they must have opposite spin. Like This Sublevels There are 4 sublevels(different shaped orbitals) s (has 1 orbital) p (has 3 orbitals) d (has 5 orbitals) f (has 7 orbitals) Can hold 2 eCan hold 6 e- Can hold 10 e- Can hold 14 e- Each orbital can hold 2 electrons Energy Level (n) Sublevels in Level 1 s 1 1 2 s 1 p 3 4 s 1 p 3 d 5 s 1 p 3 d 5 f 7 3 4 # Orbitals Total # of in Sublevel Orbitals in Level 9 16 Electron Configurations Electron Configurations: arrangement of e- in an atom There is a distinct electron configuration for each atom There are 3 rules for writing electron configurations: V.Montgomery & R.Smith 45 Aufbau Principle Aufbau Principle: an e- occupies the lowest energy orbital that can receive it. V.Montgomery & R.Smith 46 V.Montgomery & R.Smith 47 Aufbau order: 3d E 4s 3p N E 3s R 2p G 2s Y 1s V.Montgomery & R.Smith 48 V.Montgomery & R.Smith 49 Writing Electron Configurations Describes e- location. 4 3p Principal Energy Level Sublevel # of e- Electron Configuration The total of the superscripts must equal the atomic number (number of electrons) of that atom. V.Montgomery & R.Smith 51 Orbital Diagrams These diagrams are based on the electron configuration. In orbital diagrams: Each orbital (the space in an atom that will hold a pair of electrons) is shown. The opposite spins of the electron pair is indicated. V.Montgomery & R.Smith 52 Orbital Diagram Rules 1. Represent each electron by an arrow 2. The direction of the arrow represents the electron spin 3. Draw an up arrow to show the first electron in each orbital. 4. Hund’s Rule(the principle of multiplicity): Distribute the electrons among the orbitals within sublevels so as to give the most unshared pairs. Put one electron in each orbital of a sublevel before the second electron appears. V.Montgomery & R.Smith 53 Hund’s Rule One electron enters each orbital of equal energy (degenerate orbitals)until all the orbitals contain one electron with the same spin direction… …then they pair up. p orbitals p orbitals Like This Like This configuration 1s 2s H 1s1 ↑ He 1s2 ↑↓ Li 1s22s1 ↑↓ ↑ Be 1s22s2 ↑↓ ↑↓ B 1s22s22p1 ↑↓ ↑↓ ↑ C 1s22s22p2 ↑↓ ↑↓ ↑ ↑ N 1s22s22p3 ↑↓ ↑↓ ↑ ↑ ↑ O 1s22s22p4 ↑↓ ↑↓ ↑↓ ↑ ↑ F 1s22s22p5 ↑↓ ↑↓ ↑↓ ↑↓ ↑ Ne 1s22s22p6 ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ V.Montgomery & R.Smith 2px 2py 2pz 55 Orbital Diagram Examples H _ 1s Li _ 1s B 2s __ __ 1s 2s 2p N _ 1s 2s 2p V.Montgomery & R.Smith 56 Orbital filling table We can use the previous Noble Gas as an abbreviation to indicate filled inner orbitals a. Na = 1s22s22p63s1 or [Ne]3s1 b. Ca = [Ar]4s2 c. Cl = [Ne]3s23p5 d. Rb = [Kr]5s1 V.Montgomery & R.Smith 58 Dot Diagram of Valence Electrons When two atom collide, and a reaction takes place, only the outer electrons interact. These outer electrons are referred to as the valence electrons. Valence electrons are available to be lost, gained, or shared in the formation of chemical compounds V.Montgomery & R.Smith 59 Lewis Dot(electron dot) diagrams A way of keeping track of valence electrons. Write the symbol. Put one dot for each valence electron Start at 3 o’clock move in a counterclockwise direction Video X Distribute one valence electron at a time Do not pair (double up) any electrons until there is one electron in each of the four directions Pair up electrons once there is one in each of the four directions V.Montgomery & R.Smith 61 The Lewis Dot diagram for Nitrogen Nitrogen has 5 valence electrons. First we write the symbol. Then add 1 electron at a time to each side. Until they are forced to pair up. N