Quantum Mechanics Study of the behavior (motion and energy) of electrons within the atom 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) 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). Atom contains a nucleus surrounded by an electron cloud (yellow below). Nucleus is composed of protons and neutrons. Nucleus is composed of protons and neutrons. Motion of electrons is not described. 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? 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. 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 Since opposite charges attract, why don’t negatively charged electrons get pulled into the positively charged nucleus? (Science Trek, EM waves, electric force) Since opposite charges attract, why don’t negatively charged electrons get pulled into the positively charged nucleus? (Science Trek, EM waves, electric force) 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!

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!

Nature of Light Light is a form of electromagnetic radiation Light be visualized as particles – little packets of energy called photons Light can also be thought of as waves. Some of the properties of light can only be understood in terms of wave behavior.

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 )

Link to Frequency ppt Link to wavelength

Type of electromagnetic radiation is determined by its energy. Energy depends on wavelength and frequency

Electromagnetic Spectrum with Visible Light. LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY

Wave Interference When waves interact, the amplitudes can either add or subtract – a process called interference. Constructive interference - wave amplitudes add Destructive interference- wave amplitudes subtract

Constructive interference

Destructive Interference

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.

Link to phet double slit Link to double slit animation Phet simulation wave interference

2 nd Semester Units 2 nd Semester Units Quantum Mechanics – modern model of how electrons behave inside of atoms Bonding Part 1 – Ionic, Covalent, Metallic Bonding, Lewis Dot Structures Bonding Part 2 – 3 – Dimensional Drawings, Intermolecular Forces Kinetics, Equilibrium, Thermodynamics Gases