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# Minooka -Atomic Theory

## by Jeanne Erfft, teacher at Minooka on Oct 15, 2008

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## Minooka -Atomic TheoryPresentation Transcript

• Modern Atomic Theory How do electrons create the chemical trends on the Periodic Table
• Wave-Mechanical Model Assumptions
• We never know exactly how electrons move in an atom
• At any point in time there are areas around the nucleus where the electron is more likely to be (higher electron probability)
• We can make a probability map of where the electron is more likely to be
• The more intense the color on the map, the more likely the electron will be there
• Wave-Mechanical Model Assumptions (cont)
• We call the probability maps orbitals
• An orbital is the three dimensional space around the nucleus where electron probability is high
• Wave-Mechanical Model Assumptions (cont)
• The “edge” of the orbital is fuzzy, like the outer edge of the earth’s atmosphere
• Chemists and physicists arbitrarily define the orbital as containing 90% electron probability
• Three Rules for electron orbital filling
• Aufbau Principle
• Pauli Exclusion Principle
• Hund’s Rule
• When electrons occupy orbitals of equal energy, one electron enters each orbital until all of the orbitals contain one electron with parallel spins
• Then the second electron enters the orbitals with opposite spins
• Principal Components of the Wave-Mechanical Model
• Atoms have a series of energy levels called Principal Energy Levels
• A. Designated by whole numbers
• B. Symbolized by n
• - n=1, n=2, n=3, n=4
• Principal Components cont
• The energy level increases as the value of n increases
• Each Energy Level contains one or more types of orbitals called sub-levels
• The number of sub-levels (or types of orbitals) equals n (number of the energy level)
• Principal Components cont
• The number of the energy level, and the letter of the sub-level (orbital shape) are used to designate the energy level, sub-level, and orbital shape (I.e. 1s, 2p)
• An orbital can be empty or it can contain up to two electrons as long as they have opposite spins
• Principal Components cont
• The shape of the orbital indicates 90% electron probability
• -NOT the details of the electron’s movement
• Energy Levels
• Electrons fill the orbitals in order of energy, from lowest energy to highest
• The order of energy is:
• 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
• What this means is….
• 3d has a higher energy than 4s
• Even though 3d is closer to the nucleus as far as the number of the energy level
• Electrons will fill 4s before 3d
• 4s is still the outer orbital compared to 3d
• It is not Mrs. Erfft’s fault
• Mrs. Erfft is not confused
• This creates a pattern on the Periodic Table
• Explains the trends seen in much of the chemical behavior of the elements
• Electron Configuration Patterns
• The whole Periodic Table
•
• Short Form Electron Configuration
• The electron configuration for Sr is
• 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2
• The electron configuration for Kr is1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6
• Note that everything is the same through the fourth energy level (4p 6 is complete)
• Short Form Cont
• We can shorten the electron configuration for Sr by writing the electron configuration for Kr as [Kr]
• 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 =[Kr]
• Then we can write the configuration for Sr as [Kr]5s 2
• To write the short form:
• Take the electron configuration for the noble gas on the period above the element you are focusing on
• Shorten the electron configuration of the noble gas by putting the symbol of the noble gas into brackets
• Write the rest of the electron configuration to the right of the bracketed noble gas symbol in the correct order
• Valence Electrons
• Valence Electrons are the electrons in the outermost energy level of an atom
• These are the electrons in the s and p orbitals specifically
• All of the other electrons are called the core electrons
• Valence Electrons
• Are the most important electrons to chemists
• Being the outermost electrons, they are the electrons that govern the chemical behavior of the element/atom
• Valence electrons are the electrons that form bonds and are lost or gained to form ions
• Valence Electrons of Groups
• Note that the atoms in the same vertical groups on the periodic table have the same numbers of electrons in the same orbitals
• Just higher energy levels as you go down a column
• Therefore elements in the same groups show the same valence electron configuration
• Valence electron configurations
• For Chlorine
• Electron Configuration:
• [Ne]3s 2 3p 5
• Valence Configuration: 3s 2 3p 5