Light and the Quantum Mechanical Model 5.3 Light and the Quantum Mechanical Model Neon signs are formed from glass tubes. An electric current passing through the gas in each tube makes the gas glow with its own characteristic color. You will learn why each gas glows with a specific color of light.

Light as Waves amplitude: wave’s height from zero to crest. 5.3 Light Light as Waves amplitude: wave’s height from zero to crest. wavelength,  : distance between the crests. frequency,  : number of wave cycles to pass a point per unit of time. The SI unit of cycles per second is a hertz (Hz).

wavelength and frequency inversely proportional to each other 5.3 Light wavelength and frequency are inversely proportional to each other The frequency and wavelength of light waves are inversely related. As the wavelength increases, the frequency decreases.

wavelength and frequency are inversely proportional 5.3 Light c = 3  108 m/s (speed of light) c = λν wavelength and frequency are inversely proportional λ is wavelength ν is frequency

energy and frequency are directly proportional 5.3 Light E = energy in joules (J) E = hν energy and frequency are directly proportional h is Planck’s constant (6.6 x 10-34) ν is frequency

Electromagnetic Spectrum 5.3 Electromagnetic (EM) Radiation R O Y G B I V red orange yellow green blue indigo violet Electromagnetic Spectrum Lowest Energy Highest Energy The electromagnetic spectrum consists of radiation over a broad band of wavelengths. The visible light portion is very small. It is in the 10-7m wavelength range and 1015 Hz (s-1) frequency range. Interpreting Diagrams What types of nonvisible radiation have wavelengths close to those of red light? To those of blue light? (higher frequency) (shorter wavelength)

Calculate the wavelength of the yellow light emitted by the sodium lamp shown below if frequency of the radiation is 5.10 x 1014 Hz. c ν λ = c = λν Sodium vapor lamps produce a yellow glow. = 3.00 x 108 m/s 5.10 x 1014 s-1  = 5.88 x 10-7 m

Calculate the frequency of radiation with a wavelength of 4 Calculate the frequency of radiation with a wavelength of 4.50 x 10-7 m (450 nm). c λ ν = = 3.00 x 108 m/s 4.50 x 10-7 m c = λν  = 6.67 x 1014 s-1 Sodium vapor lamps produce a yellow glow.

5.1 Calculate the energy of the yellow light emitted by the sodium lamp shown below if frequency of the radiation is 5.10 x 1014 Hz. E = hν E = (6.6 x 10-34)(5.10 x 1014 Hz) E = 3.37 x 10-19 J Sodium vapor lamps produce a yellow glow.

5.1 Calculate the energy of radiation with a wavelength of 4.50 x 10-7 m (450 nm). E = hν E = (6.6 x 10-34)(3 x 108m/s) 4.50 x 10-7m E = hC  = c  E = 4.4 x 10-19 J Sodium vapor lamps produce a yellow glow.

Quick Quiz! 1. Which of the following relationships is true? A. Higher-energy light has a higher frequency than lower-energy light does. B. Higher-energy light has a longer wavelength than lower-energy light does. C. Higher-energy light travels at a faster speed than lower-energy light does. D. Higher-frequency light travels at a slower speed than lower-energy light does.

Quick Quiz. 2. The energy of EM radiation is greatest for A. visible light. B. ultraviolet light. C. infrared light. D. X-ray radiation.

Quick Quiz. 3. The longer the wavelength of light, the… A. higher the frequency. B. higher the energy. C. lower the energy. D. lower the frequency.

Atomic Emission Spectra 5.3 Atomic Emission Spectra Atomic Spectra white light gives a continuous spectrum A prism separates light into the colors it contains. For white light this produces a rainbow of colors.

atomic emission spectrum 5.3 Atomic Emission Spectra Atomic Spectra elements give discrete lines called an… A prism separates light into the colors it contains. Light from a helium lamp produces discrete lines. Identifying Which color has the highest frequency? atomic emission spectrum

Atomic Emission Spectra 5.3 Atomic Emission Spectra Atomic Spectra Mercury Nitrogen Demo DEMO: gas spectra as demo while each student has a spectrascope to view several gases displayed one at a time by teacher.

5.1 The Bohr Model Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.

Each possible electron orbit in Bohr’s model has a fixed energy. 5.1 The Bohr Model Each possible electron orbit in Bohr’s model has a fixed energy. The fixed energies an electron can have are called energy levels. A quantum of energy is the minimum amount of energy that can be gained or lost by an electron.

5.1 The Bohr Model Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced. The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level. These ladder steps are somewhat like energy levels. In an ordinary ladder, the rungs are equally spaced. The energy levels in atoms are unequally spaced, like the rungs in this ladder. The higher energy levels are closer together.

Bohr Diagrams 2, 8, 8 rule up to 2 electrons can fit in the first energy level up to 8 electrons can fit in the second energy level up to 8 electrons can fit in the third energy level How many energy levels? - The number of energy levels corresponds to the period number (row number) of the element Ex – H has one energy level; Li has two; Na has three, etc.

Bohr Diagrams H He Li 1 4 2 7 3 Complete the Bohr diagram worksheet! 2 n 3p 4 n 1 H 4 2 He 7 3 Li Complete the Bohr diagram worksheet!

What causes atomic emission spectra? 5.3 Atomic Emission Spectra Atomic Spectra What causes atomic emission spectra? Atoms absorb energy, electrons move into higher energy levels. Atoms then lose energy by emitting light when electrons return to lower energy levels. EXCITED state photon of light energy GROUND state

Atomic Emission Spectra

An Explanation of Atomic Spectra 5.3 An Explanation of Atomic Spectra Explanation of At. Emission Spectra How are the frequencies of light emitted related to changes of electron energies? A quantum of energy (as light) of a specific frequency is emitted when the electron drops to a lower energy level.

Quantum Mechanics Light and Electrons can be BOTH… particles and waves 5.3 Quantum Mechanics Quantum Mechanics Light and Electrons can be BOTH… particles and waves light particles are called photons (little packets of light)

Heisenberg uncertainty principle cannot know exactly both 5.3 Quantum Mechanics Heisenberg uncertainty principle cannot know exactly both the velocity and the position of a particle at the same time. only critical with small particles like electrons & photons. (not cars and airplanes)

The Heisenberg Uncertainty Principle 5.3 Quantum Mechanics The Heisenberg Uncertainty Principle The Heisenberg uncertainty principle states that it is impossible to know exactly both the velocity and the position of a particle at the same time.

The Quantum Mechanical Model 5.1 The Quantum Mechanical Model The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.

The Quantum Mechanical Model 5.1 The Quantum Mechanical Model Austrian physicist Erwin Schrödinger (1887– 1961) used new theoretical calculations and results to devise and solve a mathematical equation describing the behavior of the electron in a hydrogen atom. The modern description of the electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to the Schrödinger equation.

The Quantum Mechanical Model 5.1 The Quantum Mechanical Model The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller. The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.

The Quantum Mechanical Model 5.1 The Quantum Mechanical Model In the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is more dense where the probability of finding the electron is high. The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.

5.1 Atomic Orbitals An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron. Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

5.1 Atomic Orbitals Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped. The electron clouds for the s orbital and the p orbitals are shown here.

5.1 Atomic Orbitals Four of the five d orbitals have the same shape but different orientations in space. The d orbitals are illustrated here. Four of the five d orbitals have the same shape but different orientations in space. Interpreting Diagrams How are the orientations of the dxy and dx2 – y2 orbitals similar? How are they different?

5.1 Atomic Orbitals The numbers and kinds of atomic orbitals depend on the energy sublevel.

5.1 Atomic Orbitals The number of electrons allowed in each of the first four energy levels are shown here.

Quick Quiz! 1. The lines in the emission spectrum for an element are caused by the movement of electrons from lower up to higher energy levels. the movement of electrons from higher down to lower energy levels. the electron configuration in the ground state. the electron configuration of an atom.

Quick Quiz. 2. Which transition in an excited hydrogen atom will emit the longest wavelength of light? A. E5 to E3 B. E4 to E1 C. E3 to E2 D. E3 to E1 highest energy/frequency

Quick Quiz. 3. According to the Heisenberg uncertainty principle, if the velocity of a particle is known, what other quantity CANNOT be known? A. mass B. charge C. position D. spin