electrons and their movement vocabulary electromagnetic radiation electromagnetic spectrum...
Post on 27-Dec-2015
Embed Size (px)
Electrons and their MovementVocabularyElectromagnetic RadiationElectromagnetic SpectrumWavelengthFrequencyQuantumPhotonAtomic emission spectrumGround StateExcited StatePrincipal Quantum NumberPrincipal Energy LevelEnergy sublevelElectron ConfigurationAufbau PrinciplePauli Exclusion PrincipleHunds ruleValence electronsElectron-dot StructureObjectives:Define a quantum of energy, and explain how it is related to an energy change of matter.Compare the Bohr and quantum mechanical models of the atom.Use the quantum numbers to describe the electrons in an atom.Apply the Pauli exclusion principle, the aufbau principle, and Hund's rule to write electron configurations using orbital diagrams and electron configuration notation.Identify the relationships among a hydrogen atom's energy levels, sublevels, and atomic orbitals.Compare the wave and particle natures of light.Explain the impact of de Broglie's wave article duality and the Heisenberg uncertainty principle on the current view of electrons in atoms.
Review:What does a Bohr Model include?
How does this differ from Rutherfords Model?
What do we know about the Quantum Mechanical Model?RutherfordDiscovered the nucleus using the Gold Foil Exp.Rutherfords model demonstrates his findingsMostly empty space containing e-s At the center is a positive sphere (nucleus)NOTE: there arent e- orbitals or neutrons until further models
Bohr ModelAn atomic physicist, Neils Bohr developed a planetary model based on Rutherfords findingsIncluded a nucleus with neutronsElectrons moved in definite orbits (paths) around nucleus The e-s have fixed energies and do not lose energy as they orbit the nucleus
Quantum Mechanical Model(our current model)
The electrons no longer occur in orbitsIn this model, we have an idea of where the e-s could be, which is our e- cloud The electron cloud is made up of different orbitals of different shapesThe orbitals are not paths but rather probability densities
Diagram: (Fig. 13.3)
The energy levels in an atom are sort of like rungs (steps) of a ladder. The more energy an electron has, the farther away from the nucleus it usually will be. The energy levels are not evenly spaced. They get closer together as you travel farther away. To move from one rung to another requires a quantum of energy.Energy Levels7Quantum NumbersDescribe the location of the e-s around the nucleus. Quantum #s are sort of like a home address for the electron.This information about the location of the e-s in an atom can be used to:(1) determine chemical & physical properties for the elements.(2) show how the Periodic Table is organized.(3) show how and why elements combine to form compounds. The four quantum numbers are abbreviated: n, l, ml, ms
8The Principal Quantum Number: nn, the principal quantum number a) determines the overall energy of the atomic orbitalb)Tells shell numberc) May have any positive integral value from 1 to infinityexample: 1, 2, 3, 4etc.d) Tells the average distance to electron is from the nucleus-as n increases, the distance between the outermost electron and nucleus increasese) The distances can be called principal energy levels123nucleus9l: tells us which one of the orbitals in the n shell we are looking at.All of these orbital shapes are based on the probability of finding the electron in the cloud.
a) l describes the shape of the electrons momentum around the nucleus with a letter: (s, p, d, & f) These are sometimes called sublevels .
s= spherical cloudp= ellipsoid d & f orbital shapes are complex criscrossed ellipsoids, and some ds and fs are an ellipsoid with a doughnut or two around the middle.Angular momentum quantum number: l (a.k.a orbital quantum number) 10
d - orbitals
f - orbitals
s - orbitalp - orbitals11Ml : tells us the orientation of the orbital in spaceEach orbital has a specific number of orientations it can occur in:s= 1 orientation p= 3 orientations... (x, y, and z) d= 5 orientations f= 7 orientations The orientations can be represented with a line or a box.Examples: ___This means a spherical orbital at a distance of 1s1 (the number 1 is the n) to the nucleus. This orbital is centered about the x, y, and z axis. This represents an ellipsoid orbital with its 4p 3 possible orientations at a distance of 4 from the nucleus.Magnetic Quantum Number: ml12ms: spin quantum numbera) there are two possible orientations (spins) for electrons b) the two electrons may occupy the same orbital if they have different spinsms describes how the electron in an orientation is spinning around the nucleus. This spin can be thought of as up or down. (Some like to imagine it spinning clockwise and counterclockwise.) The spin is represented as an arrow in the direction of the spin.Example: This represents one electron in a spherical 2s orbital with spin up at a distance of 2 from the nucleus.Spin Quantum Number: ms13Figure 11.31: Orbitals being filled for elements in various parts of the periodic table.
14What do we do with the quantum numbers?
We said that quantum numbers are like an address for an electron but how do we write the address?
Electron configurations are used to describe the location of electrons in an element. They incorporate the four quantum numbers and are specific to each neutral element.Electrons in these configurations follow four rules:The Aufbau PrincipleThe Pauli exclusion principle (contains 2 rules)Hunds ruleRule #1: Only 2 electrons can fit into each orbitalExample: ___ ___ not ____ 1s 2s 1sRule #2: Electrons in the same orientation have opposite spins.Example: ___ not ___ 1s 1s The Pauli Exclusion Principle 16Rule #3: Electrons fill the lower energy orbitals first. -This means that energy level 1 will fill before 2.
The Aufbau Principle
Examples: 1s would be filled before 2s3s would fill before 4s
17Hunds RuleRule #4 : Bus seat rule---> Every in an orbital shape gets an electron before any orientation gets a second e-. Example: not 2p 2p
How to write an Electron ConfigurationFind the element on the periodic table. (Ne)List ALL of the prior orbital sublevels, l (w/energy level, n)Ne: 1s 2s 2p 3) Write the amount of electrons in each orbital-s: max of 2 e-p: max of 6 e-d: max of 10 e
Electron ConfigurationsPractice Problems:Write the electron configuration notation for each of the following atoms:HLiFFeBrKr20The ShorthandShorthand Method: ex: Mg1) Find the previous Noble Gas (last column on the periodic table)2) Put the chemical symbol in brackets 3) Write the remaining e- configuration
Shorthand Method contd.Practice Problems LiFFeBrKr
Electron Configurations(Energy Level Diagram)Silicon: 1s2, 2s2, 2p6, 3s2, 3p2Electron Configurations can be drawn in an ENERGY LEVEL DIAGRAM-this shows energry levels rising as the n (principle Q#) increases-this diagram can aide in the order in which the energy levels and orbitals are filled
AFTER Si, go to your notes and practice filling/drawing these for our previous examples.23Like all other rules, there are exceptions to 2 of the rules. They occur because of stability. THE FOLLOWING ELEMENTS DO THIS: Cr, Mo, Cu, Ag, Au (ANY OTHERS I WILL NOT HOLD YOU ACCOUNTABLE FOR)-Half-filled or completely filled d & f sublevels have lower energies and are more stable than partially filled ds and fs. -This means that an atom can borrow one of its s electrons from the previous orbital to become more stable.Example: ___ ___ ___ ___ ___ ___ 5s 4dbecomes___ ___ ___ ___ ___ ___ 5s 4dBecause the 4d sublevel is now full, the atom is at a lower energy state and therefore more stable.
The Exceptions24Electron Configurations & PropertiesHow do electron configurations relate to the chemical and physical properties of an element? -All elements w/ the same outer shell e- configurations have similar properties. -This means that elements in the same column (or group) have similar properties.Examples: (1) Li, Na, K, Rb, and Cs all have 1 lone s e- for their last orbital... ( 1s1, 2s1, 3s1etc.) They all react with water to produce hydrogen gas.(2) Ne, Ar, Kr, Xe, and Rn all have the outer energy level completely filled with electrons...(2s22p6, 3s23p6, 4s24p6, etc.) This makes all of them inert. (inert means it doesnt react) 25More Practice Problems (1) Which element has its last electron as a 4p5? ___________(2) Which elements are similar in properties as Bromine? __________(4) Which electron is added after 6s2? ________(5) Which element would borrow a 5s electron to get a half-filled d sublevel? ___________(6) What is the shape of the last orbital filled in Calcium, (Ca)? _____(7) How many electrons are in the last p-orbital of Sulfur, (S)? ____BromineF, Cl, I, At4f1Mosphere426What is Electromagnetic Radiation?Any wave of energy traveling at a speed of light is called electromagnetic radiation. Waves are made of photonsequivalent to a quantum of lightElectromagnetic radiation can be broken down by frequency and wavelength into seven types of radiationfrequency is the number of repeating periods over a specified time. A period is the duration of one wavelengthWavelength is the distance between the crests of a wave
Below is the electromagnetic spectrum. It shows the types of radiation from the longest to the shortest wavelength.-This order also demonstrates the lowest to highest energies.28Electromagnetic Radiation(1) Radio Waves longest wavelength, lowest energy: used in communications(2) Microwaves-- broadcasts TV sign