Chapter 5 Electronic Structure and Periodic Trends 5.2 Atomic Spectra and Energy Levels Learning Goal Explain how atomic spectra correlate with the energy levels in atoms.

Heating atoms of an element also produces light, such as the Atomic Spectra White light from the Sun or a light bulb passes through a prism or raindrops, producing a continuous spectrum, like a rainbow. Heating atoms of an element also produces light, such as the yellow color of sodium streetlights red color of a neon sign Colors are produced when electricity excites electrons in noble gases.

Photons The light emitted when atoms are heated is a stream of particles called photons. Photons are a packet of energy known as a quantum travel at the speed of light as an energy wave have both particle and wave characteristics The energy of a photon is directly proportional to its frequency.

Photons in Our World Photons play an important role in our modern world. They are used in lasers to read pits on compact discs (CDs) and digital versatile discs (DVDs) scan bar codes on merchandise labels In hospitals, high-energy photons are used in treatments to reach tumors without damaging surrounding tissues.

Learning Check Compare the frequency and wavelength of photons of ultraviolet light with that of infrared light.

Solution Compare the frequency and wavelength of photons of ultraviolet light with that of infrared light. Ultraviolet light: wavelength, 10−8 m frequency, 1016 Hz Infrared light: wavelength, 10−4 m frequency, 1013 Hz Ultraviolet light has shorter wavelengths and higher frequencies than infrared light.

Atomic Spectra When the light emitted from heated elements is passed through a prism, it does not produce a continuous spectrum. Heated elements produce an atomic spectrum that consists of different colors separated by dark areas. Only certain wavelengths of light are produced by these heated elements.

Atomic Spectra Lines produced in atomic spectra are associated with changes in the energies of electrons.

Electron Energy Levels In an atom, each electron has a specific energy level energy levels are assigned values called principal quantum numbers (n), (n = 1, n = 2. . . ) Principal Quantum Number (n) 1 < 2 < 3 < 4 < 5 < 6 < 7 Electrons in lower energy levels are closer to the nucleus.

Electron Energy Levels Electrons can only have certain energy values; we therefore say the energy of an electron is quantized. Energy levels increase in in energy as the value of “n” increases. An electron can have only the energy of one of the energy levels in an atom.

Changes in Energy Levels When electrons change from a lower to higher energy level, they absorb the energy equal to the change in energy levels. When electrons change from a higher to lower energy level, they emit energy equal to the change in energy levels.

Chemistry Link to the Environment, CFL The compact fluorescent light (CFL) is replacing standard light bulbs because it has a longer life and uses less electricity.

Chemistry Link to the Environment, CFL When a switch is turned on, electrons move between electrodes, colliding with mercury atoms in a mixture of gas. When electrons in the mercury atoms absorb energy from the collisions, they move to a higher energy level.

Chemistry Link to the Environment, CFL As the electrons fall to lower energy levels emitting ultraviolet radiation, they strike the phosphor coating inside the bulb emitting fluorescent light. Fluorescent bulbs are more efficient, using up to 70% less energy than their incandescent counterparts.

Learning Check In each of the following energy level changes, indicate if energy is (1) absorbed (2) emitted (3) not changed A. An electron moves from the first energy level (n =1) to the third energy level (n = 3). B. An electron falls from the third energy level to the second energy level. C. An electron moves within the third energy level.

Solution In each of the following energy level changes, indicate if energy is (1) absorbed (2) emitted (3) not changed A. An electron moves from the first energy level (n =1) to the third energy level (n = 3). (1) The electron is moving from a lower to a higher energy level; energy is absorbed.

Solution In each of the following energy level changes, indicate if energy is (1) absorbed (2) emitted (3) not changed B. An electron falls from the third energy level to the second energy level. (2) The electron moves from a higher to a lower energy level; energy is emitted.

Solution In each of the following energy level changes, indicate if energy is (1) absorbed (2) emitted (3) not changed C. An electron moves within the third energy level. (3) Energy is not changed when electrons stay in the same energy level.