Modern Physics Lesson 1: Intro to Quantum Mechanics and Photoelectric Effect Lesson 2: Energy Levels Lesson 3: E = mc^2 Lesson 4: Standard Model of

Transcription

1 Modern Physics Lesson 1: Intro to Quantum Mechanics and Photoelectric Effect Lesson 2: Energy Levels Lesson 3: E = mc^2 Lesson 4: Standard Model of Particle Physics

2 Pass up your homework

3 Energy is Quantized and can only gain or lose kinetic energy only in fixed amounts, or quanta.

4 It is possible to change energy level by absorbing or emitting a quantum of energy in the form of a photon.

5 Ground State: Lowest possible state for an electron in an atom Ionization energy: Energy needed to liberate an electron from that level

6 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What minimum energy did this photon have?

7 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What minimum energy did this photon have? 13.6 ev

8 What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?

9 What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon? The electron will leave the atom with a kinetic energy of 2.0 ev.

10 Level Jumps Equation E = E - photon i E f An electron will jump to a higher level if the ABSORBED photon has exactly the right energy. When an electron drops to a lower level a photon is EMITTED

11 What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level?

12 What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level? 12.75eV

13 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the energy of the emitted photon?

14 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the energy of the emitted photon? E photon = E i E f E photon = ev ev E photon = ev

15 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon?

16 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon? Step 1: Recognize which equation we are going to use. We want to find the frequency of a photon

17 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon? Step 1: Recognize which equation we are going to use. We want to find the frequency of a photon Ephoton = hf

18 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon? Step 2: Realize that we already have the energy for the photon going from n = 4 to n = 3 In the last problem, we calculated it to be: Ephoton = +0.66eV

19 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon? Step 3: We actually can t plug it directly into the equation yet because planks constant (6.63x10^-34J*s) is given in terms of Joules, not electron volts, so first we must convert the energy to joules

20 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon? E photon = hf x J = (6.63 x J s) f f =1.6 x Hz

21 Note: The reference table gives you the ionization energy for hydrogen and mercury. The concept is the same.

22 Homework Pages Questions 12-34, except 18, 21, 22 Please do your homework on loose leaf

23