Quantum Mechanics Study of the behavior (motion and energy) of electrons within the atom Importance: Energy arrangement of electrons within the atom determines chemical behavior (how atoms react)
Rutherford Model of the Atom Atom contains a nucleus surrounded by an electron cloud (yellow below). Nucleus is composed of protons and neutrons. Motion of electrons is not described.
According the Laws of Physics known in 1911 the Rutherford model of the atom should have been unstable – Atoms and things made of atoms (like people) should not exist!
Important Question Raised by Rutherford Model Since opposite charges attract, why don’t negatively charged electrons get pulled into the positively charged nucleus? Laws of physics known in 1911 predict if there are no restrictions placed on the motion and energy of electrons inside an atom, electrons should circle closer and closer to the nucleus and eventually end up in the nucleus.
Question Raised by Rutherford Model If no restrictions are placed on the motion and the energy of the electron, the electron should be pulled into the nucleus. Link to Models of Hydrogen atom Phet applet
The Atom is Stable! Since e- do NOT get pulled into the nucleus it was very clear to scientists in 1911 that there were very important properties of the electron that no one understood! Work HW 8-1, p. 24
How do you investigate the behavior of electrons moving near the speed of light inside an atom? Answer: The behavior of electrons inside an atom can be explored by investigating the interaction of light energy with matter!
Light is a form of electromagnetic radiation Work HW 8-2, #1 Light is a form of electromagnetic radiation Electromagnetic is a form of energy traveling through space Electromagnetic radiation travels at the speed of light -186,000 mi/s or 3 x 108 m/s
Nature of Light – Dual Nature as Particle and Wave Confusing Concept – In some experiments light acts like a particle; in other experiments it acts like a wave
Dual Nature of Light as Particle and Wave Light be visualized as particles – little packets of energy called photons Photoelectric effect – light striking object such as metal can knock electrons loose (Analogy – bullets chipping off pieces of rock) Work HW 8-2, #1-4
Wave Properties of Light Light can also be thought of as waves. Some of the properties of light can only be understood in terms of wave behavior. Work HW 8-2, #4 Wave on a String Phet Link to Frequency ppt Work HW 8-2, #3
Wavelength and Amplitude Wavelength – distance between 2 wave crests or troughs Amplitude- height of wave
Frequency Frequency – the number of wave crests that pass a fixed point per second As wavelength↓, frequency ↑ Frequency is measured in hertz (s-1)
Type of electromagnetic radiation is determined by its energy Type of electromagnetic radiation is determined by its energy. Energy depends on wavelength and frequency
Electromagnetic Spectrum with Visible Light. HIGH ENERGY LOW ENERGY Work HW 8-1, #
Wave Interference When waves interact, the amplitudes can either add or subtract – a process called interference. CONSTRUCTIVE INTERFERENCE – wave amplitudes ADD +2 +1 +1 -1 -1 +1
Destructive Interference
Link to phet double slit Phet simulation wave interference Link to double slit animation Work HW 8-2, #6-12
Double Slit Experiment Light projected on a screen through 2 slits shows dark areas where light disappears and bright areas where intensity of light increases. Result can only be explained by concept of wave interference.
Constructive interference