Atomic Structure and Electron Configuration

Rapid Learning Center Chemistry :: Biology :: Physics :: Math Rapid Learning Center Presenting Teach Yourself High School Chemistry in 4 Hours 1/56 http://www.rapidlearningcenter.com Atomic Structure and Electron Configuration Rapid Learning Core Tutorial Series Wayne Huang, PhD Kelly Deters, MA Russell Dahl, PhD Rapid Learning Center www.rapidlearningcenter.com/ Rapid Learning Inc. All rights reserved. Rapid Learning Inc. All rights reserved. 1

Objectives By studying this tutorial you will learn Basic structure of atoms How to determine the number of electrons How to place electrons in energy levels, subshells and orbitals How to show electron configurations using three methods How to write and understand Quantum Numbers 3/56 Electron Configuration Concept Map Previous Previous content content New New content content Chemistry Chemistry Quantum Numbers Location described by Studies Matter Matter Made of Electrons Chemical properties determined by Atoms Atoms 3 ways to show configurations Boxes Boxes and and Arrows Arrows 4/56 Spectroscopic Notation Noble Noble Gas Gas Notation Rapid Learning Inc. All rights reserved.

Atomic Structure 5/56 Definition: Atom Atom - n. smallest piece of matter that has the chemical properties of the element. Often called the Building Block of Matter 6/56 Rapid Learning Inc. All rights reserved. 3

What s in an Atom? An atom is made of three sub-atomic particles. Particle Location Mass Charge Proton Nucleus 1 amu = 1.67 10-7 kg +1 Neutron Nucleus 1 amu = 1.67 10-7 kg 0 Electron Outside the nucleus 0.00055 amu 9.10 10-31 kg -1 1 amu ( atomic mass unit ) = 1.66 10-7 kg 7/56 The Atom Nucleus Electron cloud Mass = # of protons + # of neutrons Charge = # of protons Charge = - (# of electrons) Very small relative mass Overall Charge = # of protons - (# of electrons) Overall Mass = # of protons + # of neutrons 8/56 Rapid Learning Inc. All rights reserved. 4

Protons Versus Electrons Protons Electrons + Charge -Charge Contributes to mass of atom Found in nucleus Does not contribute significantly to mass of atom Found outside nucleus 9/56 # determines the identity of the atom Cannot be lost or gained without changing which element it is (nuclear reaction) # and configuration determine how the atom will react Can be lost or gained results in an atom with a charge (ion) The ratio of protons to electrons determines the charge on the atom. Electron Locations 10/56 Rapid Learning Inc. All rights reserved. 5

Definition: Electron Cloud Electron cloud It is the area outside of the nucleus where the electrons reside. 11/56 Electron Clouds Electron cloud Principle energy levels The electron cloud is made of energy levels. Subshells Energy levels are composed of subshells. Orbitals Subshells have orbitals. 1/56 Rapid Learning Inc. All rights reserved. 6

Definition: Subshell and Orbital Subshell A set of orbitals with equal energy. Orbital Area of probability of the electron being located. Each orbital can hold electrons. 13/56 Types of Subshells There are 4 types of subshells that electrons reside in under ordinary circumstances. Subshell Begins in energy level Number of equal energy orbitals Total number of electrons possible Energy increases s p d 1 3 1 3 5 6 10 f 4 7 14 14/56 Rapid Learning Inc. All rights reserved. 7

Definition: Electron Configurations Electron Configurations Shows the grouping and position of electrons in an atom. Since the number of electrons and their configuration determines the chemical properties of the atom, it is important to understand them. Electron configurations use boxes for orbitals and arrow for electrons. 17/56 Aufbau Principle The first of 3 rules that govern electron configurations 1 Aufbau Principle: Electrons must fill subshells (and orbitals) so that the total energy of atom is at a minimum. What does this mean? Electrons must fill the lowest available subshells and orbitals before moving on to the next higher energy subshell/orbital. 18/56 Rapid Learning Inc. All rights reserved. 9

Energy and Subshells The energy diagram below shows the relative energy levels. 6s 5s 4s 6p 5p 4p 5d 4d 3d 4f 3p 3s s p Subshells are filled from the lowest energy level to increasing energy levels. Energy 19/56 Not that this does not always go in numerical order. Hund s Rule The second of 3 rules that govern electron configurations. Hund s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up. How does this work? If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up. 0/56 Rapid Learning Inc. All rights reserved. 10

Pauli Exclusion Principle The last of 3 rules that govern electron configurations. 3 Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins. Spin describes the angular momentum of the electron Spin is designated with an up or down arrow. How does this work? If you need to add 4 electrons to a p subshell, you ll need to double up. When you double up, make them opposite spins. 1/56 Determining the Number of Electrons In order to properly construct an electron configuration, you must be able to determine how many electrons to use. Charge = # of protons # of electrons Atomic number = # of protons Example: Br 1- How many electrons does the following have? Charge = -1 Atomic number for Br = 35 = # of protons -1 = 35 - electrons Electrons = 36 /56 Rapid Learning Inc. All rights reserved. 11

Another Example In order to properly construct an electron configuration, you must be able to determine how many electrons to use. Charge = # of protons # of electrons Atomic number = # of protons Example: Cl How many electrons does the following have? No charge written Charge is 0 Atomic number for Cl = 17 = # of protons 0 = 17 - electrons Electrons = 17 3/56 Applying the Rules Use the 3 rules of electron configurations. 1 Aufbau Principle: Electrons must fill subshells (and orbitals) so that the total energy of atom is at a minimum. 3 Hund s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up. Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins. Example: Cl Give the electron configuration for a Cl atom No charge written Charge is 0 Atomic number for Cl = 17 = # of protons 0 = 17 - electrons Electrons = 17 Place 17 electrons 431567910 11 1 13 14 16 17 8 s p 3s 3p 4/56 Rapid Learning Inc. All rights reserved. 1

Spectroscopic Notation 5/56 Definition: Spectroscopic Notation Spectroscopic Notation Shorthand way of showing electron configurations. The number of electrons in a subshell are shown as a superscript after the subshell designation. s p 3s 3p s p 6 3s 3p 5 6/56 Rapid Learning Inc. All rights reserved. 13

Writing Spectroscopic Notation 1 3 4 Determine the number of electrons to place. Follow Aufbau s Principle for filling order. Fill in subshells until they reach their max (s =, p = 6, d = 10, f = 14). The total of all the superscripts is equal to the number of electrons. Example: Give the spectroscopic notation for S. S No charge written Charge is 0 Atomic number for S = 16 = # of protons 0 = 16 - electrons Electrons = 16 Place 16 electrons + + 6 + + 4 = 16 7/56 s p 6 3s 3p4 Electron Configurations and the Periodic Table 8/56 Rapid Learning Inc. All rights reserved. 14

Configurations Within a Group Look at the electron configurations for the Halogens (Group 7). F s p 5 Cl s p 6 3s 3p 5 Br s p 6 3s 3p 6 4s 3d 10 4p 5 I s p 6 3s 3p 6 4s 3d 10 4p 6 5s 4d 10 5p 5 All of the elements in Group 7 end with 5 electrons in a p subshell. 9/56 Configurations and the Periodic Table In fact, every Group ends with the same number of electrons in the highest energy subshell. Each area of the periodic table is referred to by the highest energy subshell that contains electrons. s-block p-block d-block s 1 s p 1 p p 3 p 4 p 5 p 6 d 1 d d 3 d 4 d 5 d 6 d 7 d 8 d 9 d 10 f-block 30/56 f 1 f f 3 f 4 f 5 f 6 f 7 f 8 f 9 f 10 f 11 f 1 f 13 f 14 Rapid Learning Inc. All rights reserved. 15

Periodic Table as a Road-Map Wondering how to remember the order of filling of the subshells? Just use the periodic table. 31/56 In order to do this, the f block needs to be placed in atomic order. (It s usually written below to fit it on the paper) Periodic Table as a Road-Map To see the filling order of subshells, read from left to right, top to bottom! This tool shows that the 3d energy level is filled after the 4s energy level! s 3s 4s 5s 6s 7s 4f 5f 3d 4d 5d 6d p 3p 4p 5p 6p s subshells begin in level 1, so begin the s-block with p subshells begin in level, so begin the p-block with p d subshells begin in level 3, so begin the d-block with 3d f subshells begin in level 4, so begin the f-block with 4f 3/56 Rapid Learning Inc. All rights reserved. 16

Another Tool for Filling Order There is another tool commonly used to remember orbital filling order. s p 3s 3p 3d 4s 4p 4d 4f To read the charge, move down one diagonal as far as possible, then jump to the top of the next diagonal and keep going. 5s 5p 5d 5f 6s 6p 6d 7s 7p 33/56 8s Electron Configurations of Ions 34/56 Rapid Learning Inc. All rights reserved. 17

Definition: Ion Ion an atom that has gained or lost electrons resulting in a net charge. Atoms gain and lose electrons to be in a more stable state. Usually, the more stable state is a full valence shell. Outermost shell of electrons 35/56 Full Valence Shell Ions Look at the electron configurations for the following: Br -1 p = 35-1 = 35 - e e = 36 s p 6 3s 3p 6 4s 3d 10 4p 6 O - p = 8 - = 8 - e e = 10 s p 6 Na + p = 11 +1 = 11 - e e = 10 s p 6 Ca + p = 0 + = 0 - e e = 18 36/56 s p 6 3s 3p 6 Rapid Learning Inc. All rights reserved. 18

Full Valence Shell Ions What do you notice about each of these configurations? They all end with full p subshells. Br -1 s p 6 3s 3p 6 4s 3d 10 4p 6 O - Na + s p 6 Notice that O - and Na + have the same number and configuration of electrons. This makes them isoelectric. s p 6 Ca + 37/56 s p 6 3s 3p 6 Noble Gas Configuration 38/56 Rapid Learning Inc. All rights reserved. 19

Definition: Noble Gas Notation Noble Gas Group 8 of the Periodic Table. They contain full valence shells. Noble Gas Notation Noble gas is used to represent the core (inner) electrons and only the valence shell is shown. Br Spectroscopic s p 6 3s 3p 6 4s 3d 10 4p 5 Noble gas [Ar] 4s 3d 10 4p 5 39/56 The [Ar] represents the core electrons and only the valence electrons are shown. Which Noble Gas Do You Choose? How do you know which noble gas to use to symbolize the core electrons? Think: Price is Right. How do you win on the Price is Right? By getting as close as possible without going over. Choose the noble gas that s closest without going over! 40/56 Noble Gas He Ne Ar Kr Xe # of electrons 10 18 36 54 Rapid Learning Inc. All rights reserved. 0

Where Does the Noble Gas Leave Off? How do you know where to start off after using a noble gas? Use the periodic table! s 3s 4s 5s 6s 7s 4f 5f 3d 4d 5d 6d p 3p 4p 5p 6p He Ne Ar Kr Xe Rn The noble gas fills the subshell that it s at the end of. 41/56 Begin filling with the s subshell in the next row to show valence electrons. Noble Gas Notation Example 1 3 Determine the number of electrons to place. Determine which noble gas to use. Start where the noble gas left off and write spectroscopic notation for the valence electrons. Example: As Give the noble gas notation for As. No charge written Charge is 0 Atomic number for As = 33 = # of protons 0 = 33 - electrons Electrons = 33 Place 33 electrons Closest noble gas: Ar (18) Ar is full up through 3p 4/56 [Ar] 4s 3d 10 4p 3 18 + + 10 + 3 = 33 Rapid Learning Inc. All rights reserved. 1

Comparing the Different Notations 43/56 Pros and Cons of Each Notation Each notation has it s advantages and disadvantages. Boxes and arrows Pro Shows if electrons are paired or unpaired Con Longest method Spectroscopic notation Noble Gas notation Quicker than Boxes and arrows Allows focus on the valence electrons (that control bonding) Quickest method Does not show pairing of electrons Does not show core electrons Does not show pairing of electrons 44/56 Rapid Learning Inc. All rights reserved.

Exceptions to the Aufbau Rule 45/56 Stability of d Subshells with 5 or 10 d subshells have 5 orbitals They can hold 10 electrons. According to the Aufbau principle, Cr should have the following valence electron configuration: 4s 3d 4 But a half-full or completely full d subshell is more stable than the above configuration, so it is: 4s 1 3d 5 46/56 Rapid Learning Inc. All rights reserved. 3

Elements with Exceptions The following elements are excepts to the Aufbau Principle: Element Should be Actually is Cr Mo W Cu Ag Au 4s 3d 4 4s 1 3d 5 5s 4d 4 5s 1 4d 5 6s 5d 4 6s 1 5d 5 4s 3d 9 4s 1 3d 10 5s 4d 9 5s 1 4d 10 6s 5d 9 6s 1 5d 10 They are the two groups on the periodic table that begin with Cr and Cu. 47/56 Quantum Numbers 48/56 Rapid Learning Inc. All rights reserved. 4

Definition: Quantum Numbers Quantum Numbers A set of 4 numbers that describes the electron s placement in the atom. 49/56 4 Quantum Numbers n m l, 1, -1, + ½ l m s Quantum Number Symbol Describes Possible Numbers Principal n Shell number Whole #s 1 Azimuthal l Subshell type Whole # < n Magnetic m l Orbital -l + l Spin m s Spin + ½ or ½ 50/56 Rapid Learning Inc. All rights reserved. 5

Determining Quantum Numbers n: principal energy level 4p 3 Give the number of the shell l: subshell s = 0 p = 1 coding system d = f = 3 m l : orbital s 0 p -1 0 1 d - -1 0 1 Number-line system of identifying orbitals. 0 is always in the middle. Number line from l to + l f -3 - -1 0 1 3 m s : spin Coding system = + ½ = - ½ 51/56 Quantum Number Examples Example: Give the quantum numbers for the red arrow. s p 3s 3p 0 It s in level 3 It s in subshell s the code for s is 0 It s in orbital 0 It s a down arrow, 3, 0, 0 -½ Example: Give the quantum numbers for the red arrow. 5/56 s p 3s 3p -1 0 +1 It s in level It s in subshell p the code for p is 1 It s in orbital -1,, 1, -1 + ½ It s an up arrow Rapid Learning Inc. All rights reserved. 6

Identifying Incorrect Quantum Numbers Example: What s wrong with the following sets of quantum numbers? 1, 1, 0, + ½ n = 1 OK as n (energy level) can be any whole # > 0 l = 1 subshell is p There is no p subshell in energy level 1, 1, -, - ½ n = OK as n can be any whole # >0 l = 1 subshell is p OK as level has p m l = - on the - orbital p subshell has 3 orbitals: No - orbital in a p subshell. m l must be between l and l -1 0 +1 53/56 1, 0, 0, -1 n = 1 OK as n can be any whole # >0 l = 0 subshell is s OK as level 1 has an s m l = 0 on the 0 orbital OK as s has 1 orbital and it s 0 m s = -1 m s must be either + ½ or ½ Summary Electron configurations can be shown with boxes and arrows, in in spectroscopic notation, or noble gas notation. Atoms are made of of protons, neutrons and electrons. The configuration of of the electrons determines the chemical properties of of the atom. Quantum numbers describe the location of an electron in an atom and are a series of 4 numbers. Electrons are organized in levels, subshells and orbitals. Electron configurations are written following the Aufbau principle, Hund s Rule and the Pauli Exclusion Principle. 54/56 Rapid Learning Inc. All rights reserved. 7

Rapid Learning Printable Tutorial - 13 Congratulations You have successfully completed the core tutorial Atomic Structure and Electron Configuration Rapid Learning Center Rapid Learning Center Chemistry :: Biology :: Physics :: Math What s Next Step 1: Concepts Core Tutorial (Just Completed) Æ Step : Practice Interactive Problem Drill Step 3: Recap Super Review Cheat Sheet Go for it! 56/56 Rapid Learning Inc. All rights reserved. http://www.rapidlearningcenter.com 8