The Bohr Model

Do Now (3/24/14) (5 Minutes)  If you haven’t already Pass in Last week’s Do Now  What are some scientific examples of concepts humanity or yourself believed in the past but we now think differently? Myths  Earth is flat and the center of universe  The Earth is 6000 years old  Heavier Objects Fall Faster than Smaller Objects  Washing your hands before surgery  Atoms are the smallest possible particles

History of the Atom

Notesheet  Writing down notes helps you remember material before you even start studying.  What should I write down?  What the professor thinks is important.  Repetition/Emphasis  Don’t copy down everything on the board!!!!

What do we know about the ATOM?  Talk with your table for 1 minute about what you already know about the atom.  I will call on three random people in the class to see what you discussed.  How big is it?  What is an atom made of?  What does it look like?

Dalton  1803 John Dalton an "atomic theory" with spherical solid atoms 1) All elements are made up of tiny spherical particles called atoms 2) Atoms can not be created or destroyed

JJ. Thompson  1904 JJ. Thompson Plum Pudding model Negative Electrons are the Plums Positive Pudding makes up the rest of the space

Quick, Discuss with your Elbow Partner  What are the three major particles that make up atoms?  Which particle has a positive charge?  Proton  Which particle has a negative charge?  Electron  Which particle has a neutral charge?  Neutron

Ernest Rutherford  1911 Ernest Rutherford  Nucleus of an atom was:  very dense,  very small  positively charged.  Electrons were located outside the nucleus. What is in-between the Nucleus and the Electrons? Empty Space!!!

View of atomic Structure in early 1900’s electrons traveled around the nucleus in orbits, like the planets Classical (before 1900) physics could not explain why electrons don’t fall into the nucleus

Video  - How did J.J. Thomson describe the atom?  Plum Pudding Model  - What model did Rutherford use to describe the atom?  A Nucleus with electrons around the outside  - Why did the scientists have to adjust their model of the atom?  Experimental data.

Classwork  Spend the rest of class finishing the video questions and the exit ticket.

Notesheet  Why should you write notes?  Writing down notes helps you remember material before you even start studying.

Notesheet  What should I write down?  What the professor thinks is important.  Repetition/Emphasis  Don’t copy down everything on the board!!!!

Do Now (3/25/14) (5 minutes): 1. Describe the structure of an atom. 2. Draw a picture of an atom. 1. (I will need three volunteers to draw their atom)

Rutherford’s Model How did Rutherford describe the motion of electrons around the nucleus? Classical (before 1900) physics could not explain why electrons don’t fall into the nucleus

Rutherford Model  This is a big flaw in Rutherford’s model.  They didn’t know why electrons don’t hit the nucleus?

Bohr Model  Bohr claimed that electron can have only certain energy levels.

 The way we describe the energy levels is by using quantum numbers ‘n’  Only orbits where n =positive integer are permitted. Energy of quantized state n = 1 n = 2

Quantum States  Further from the nucleus means more energy  There is no “in between” energy

Energy of one electron:  E of an electron:

Guided Practice (2 minutes) Calculate the energy of an electron on the second energy level, E 2, of the hydrogen atom. What equation should we use for this? E n =-13.6/n 2 What are the knowns and unknowns??? N = 2 E 2 = ??? -3.4eV

Quantum States  Can we have an energy level of 2.5?  NO!!!!

Radius of electron orbits:

Practice (2 minutes) Calculate the radius of an electron on the third energy level, E 3, of the hydrogen atom. 47.7x10^-11m

Ionization  The ionization energy is equal to the negative energy of the electron Ionization energy is the energy to remove an electron. E ionization = -E n

Practice  What is the ionization energy of a hydrogen atom that is in the n = 3 excited state?  1.51 eV

Classwork  Spend the rest of class working on “Bohr Atom Classwork”.  It is due Thursday.  For Problems 5 and 6 the energy should be negative.

Do Now (3/26/14) (5 minutes): 1)What is the energy associated with an electron in the ground state of a hydrogen atom? 2) What is the energy change when an electron drops from E 5 to E 1 in an excited hydrogen atom?

Do Now Quiz (5 Minutes)  What is the energy change of an electron in the fourth energy level of a hydrogen atom that drops to the second energy level?

Talk with your group (1 minute)  When an electron drops from a higher state to a lower state, what happens to it’s energy?  The electron’s energy decreases!

The Bohr Model  When an electron loses energy and drops to a lower state, a photon is released with energy:

E of photon:  Another way to look at it:

How can I visualize this?

Example (3 minutes):  An electron drops from the 6 th energy state to the 3 rd. What is the energy of the photon emitted?  1.13eV

Classwork  Spend the rest of class working on “The Bohr Atom”.  It is due Tuesday.  By the end of class you need to have a minimum of 6 problems completed.  This will be worth points towards the assignment.

Do Now (3/27/14) (5 minutes): 1)What is the energy of the photon emitted by an electron that jumps from the sixth energy level to the second energy level?

Different types of Atoms  So far, we have been working with atoms of a certain element. What type of atoms have we been studying so far this week?  Hydrogen Atoms

Hydrogen-like Atoms  (atoms that have been ionized so that they have one electron left) Where Z is the Atomic Number

Hydrogen-like Atoms  (atoms that have been ionized so that they have one electron left) Where Z is the Atomic Number

Other Atoms  The previous equations were for “Hydrogen-Like” Atoms  (atoms that have been ionized so that they have one electron left)  Will these equations work for all atoms?  NO

Practice (3 minutes) Calculate the radius of an electron on the third energy level, E 3, of an ionized helium atom. (Z = 2) 2.38x m

Guided Problem(7 minutes): 1)What is the frequency of the photon emitted by an electron that jumps from the third energy level to the second energy level? What are the givens and what are we solving for? Photon starts at E 3 Photon falls to E 2 We want to solve for the FREQUENCY of the PHOTON

Guided Problem (7 minutes)  We want to solve for the FREQUENCY of the PHOTON  What is an equation we’ve learned previously for the Frequency of a Photon?  E = hf  Is this energy in Joules or eV?  It must be in Joules!!!

Guided Problem (7 minutes) E = hf  If we want to solve for frequency, what other variable in this equation do we need to find?  The energy of the photon!!!

Guided Problem (7 minutes)  With our givens of, E 3 and E 2, how can we solve for the energy of the photon?

Guided Problem (7 minutes)  Let’s Summarize  We want to solve for ____???  The Frequency of the photon  The equation we use for frequency is???  E = hf  This equation gives us the energy of the photon

Guided Problem (7 minutes)  Let’s Summarize  How do we get the energy of the photon?

Guided Problem (7 minutes)  Let’s Solve

Quiz Review  Monday we are going to do a Gallery Walk.  Each table will be assigned a problem off the quiz review sheet.  You will write out your solution on a blank piece of printer paper.  It doesn’t have to be colorful just clear and easy to read.

Quiz Review  BRING YOUR COMPLETED SOLUTION WITH YOU MONDAY You will not get more class time to write out your solution

Rubric  You will get three minutes per question to look over it and grade their solution

Today’s Classwork  Work on your Quiz Review sheet  Once everyone at a table has finished two problems I will assign you a problem off the Quiz Review for Monday.  You may check your answer with the key and when you have the right answer I can give you printer paper.

Do Now (3/31/14) (5 minutes):  List at least three different equations and come up with two problem solving tips that should be on your notecard for Tomorrow’s Quiz. E photon = hf = E higher state - E lower state E n = -13.6/n 2 r n = n 2 *(5.3x ) When an photon is released, Energy Change is Higher – Lower Further the electron is away more required energy If E photon > E ionizization = than the electron is ejected

Gallery Walk (5 Minute Prep)  Take out your Quiz Review Solution  You will move from one table to another in chronological order.  Three minutes per table  If you finish early at a table, Bonus points if you give suggestions on how to improve a solution.

Gallery Walk  Check each groups’ solution against the answer key provided for you.  Bonus points if you give suggestions on how to improve a solution.  Fill out the rubric for each group, make sure to leave your slot on the rubric blank.

Transition (1 Minute)  Pass on your Rubrics and take out any notes you wish to use for the Multiple Choice Review

Multiple Choice 1) When does an electron emit a photon? a) when it reverses its movement around the nucleus b) when it stays in the same energy level c) when it jumps from the fourth to the third energy level d) when it jumps from first to the second energy level Answer: C

Multiple Choice 2) In which energy level transition will the emitted photon have the highest frequency? A. from n = 5 to n = 1 B. from n = 4 to n = 1 C. from n = 3 to n = 1 D. from n = 2 to n = 1 Answer: A

Multiple Choice 3) What is the frequency of the photon emitted when an electron drops from E 5 to E 4 in an excited hydrogen atom? A x Hz B x Hz C x Hz D x Hz Answer: C

Multiple Choice 4) What is the radius of the orbital associated with the energy level E 5 of the hydrogen atom? A x m B x m C x m D x m Answer: B

Multiple Choice 5) A hydrogen atom electron has an energy of eV when it is in the second energy level. What is the minimum energy necessary to ionize the hydrogen atom if the electron is in the second energy level? A eVC eV B. 3.4 eVD eV Answer: B

Quiz Review  Spend the rest of class finishing up your Quiz Review Paper.  Make sure to make a notecard!!!  I will be here after school today until 4pm.

Rubric  You will get three minutes per question to look over it and grade their solution

The Bohr Model of the Atom 3/10/14

Do Now (3/29/12):  An electron is in energy state #5. 1. What is the radius of the orbit? 2. What is the energy of the electron?

Energy Level Diagrams  Minimum energy to remove an electron is binding energy or ionization energy.  13.6eV – energy required to remove an electron from the lowest state E 1 = -13.6eV up to E=0.  Lyman series, Balmer series, Paschen series for hydrogen atoms. – pg 848.

Practice:  Complete the Bohr Atom classwork  Check your answers with the key at the front of the room  When you get 100%, submit your work and begin to work on your homework

Energy Transitions in Atoms Energy of photon = Energy lost by electron hf = E i - E f

Calculating Wavelengths of Emitted Light hf = E i - E f E 3 ---> E 2 : E i = eV E f = eV hf = (-3.40) = 1.89 eV = (1240 eV-nm) / E = 1240 / 1.89 = 656 nm