Chemistry 111 Name Atoms are very tiny In fact they re smaller than the wavelengths of visible light o Individual atoms can t be seen with visible light in the usual sense but they interact with light in characteristic ways Electronic Structure o Electromagnetic Radiation The electromagnetic spectrum Arranges forms of energy from lowest to highest Arranges wavelengths from longest to shortest Shows visible light from 700 400 nm o Electrons in the Atom White light that passes through a prism Chemistry Questions o Why is the Sky Blue Electronic Structure o Electrons in the Atom Is separated into all the visible colors that together are called a continuous spectrum Gives the colors of a rainbow R O Y G B I V An atomic spectrum consists of lines of different colors forms when Light from a heated element passes through a prism or Electrons drop to lower energy levels and emit photons Sunlight is made of all the colors of the rainbow The gas molecules in the atmosphere interact with the sunlight before it reaches our eyes scattering high energy blue light more than low energy red light This phenomenon known as Rayleigh scattering fills the sky with scattered blue waves giving it a blue appearance During sunrise or sunset sunlight must travel through a greater thickness of atmosphere Even more light is scattered making the sun look redder and the sky orange or pink a In a spectroscope light emitted by atoms passes through a narrow slit and is separated into particular frequencies by a diffraction grating b A spectra of colors appear to the left and right of the slit c Elements heated by a flame glow a characteristic color When viewed through a spectroscope the color of each element consists of a pattern of distinct frequencies known as an atomic spectrum Page 1 Chemistry 111 Name o Electromagnetic Radiation Why is electronic structure important electrons How do we study atomic structure All of chemistry is governed by the transfer or rearrangement of o Electrons in the Atom Scientists use the interaction of light with matter to study electronic structure From his studies with light in 1914 Niels Bohr proposed a model of the hydrogen atom as a nucleus with an electron circling around it In this model the energy levels of the orbits are quantized so that only specific orbits corresponding to certain specific energies are available 1 2 3 etc in energy higher in energy Electrons do not move freely in space An electron is confined to a specific region giving it a particular energy The regions are called principal energy levels or shells n numbered n Electrons in lower numbered shells are closer to the nucleus and are lower Electrons in higher numbered shells are further from the nucleus and are Light is quantized which means it consists of a stream of energy packets Each packet is called a photon In the electron clouds of each element only specific energies levels are allowable Electrons absorb energy to jump to higher energy levels When an electron falls to a lower energy level energy is energy is emitted as a photon of light In the visible range this energy appears as a color Elements and compounds have distinct energy levels thus they give off o In each of the following energy level changes indicate if energy is absorbed emitted or not changed level n 3 An electron moves from the first energy level n 1 to the third energy An electron falls from the third energy level to the second energy level An electron moves within the third energy level o In each of the following energy level changes indicate if energy is absorbed emitted or not changed energy level n 3 energy level Absorbed an electron moves from the first energy level n 1 to the third Emitted an electron falls from the third energy level to the second Page 2 Learning Check specific atomic spectra Chemistry 111 Name Not changed an electron moves within the third energy level Chemistry Questions o What gives fireworks their color Metal Na NaCl K KCl Sr 2 Sr NO3 2 Ba 2 Ba NO3 2 Cu 2 Cu NO3 2 Color yellow light 600nm purple light 320nm red light 700nm green light 550nm blue light 450nm Burning causes excitement of e from low energy states to high energy states As the e relaxes back down to the ground state excess energy is released as a photon of light o How do Glow in the dark Toys Work All glow in the dark products contain phosphors A phosphor is a substance that radiates visible light after being energized Glow in the dark toys use phosphors that energize in normal light and have a very long persistence typically Zinc Sulfide and Strontium Aluminate The light in the room energizes the phosphors and excites their electrons called phosphorescence This photon energy is temporarily stored in the atom When the electrons slowly lose this extra energy it creates a dim glow When the material releases all the photons it has stored it needs to be recharged Structure of the Atom o Atomic Number From the periodic table 3 Li Atomic Number Z is the number of protons in the nucleus Every atom of a given element has the same atomic number Every atom of a given element has the same number of protons in the nucleus Different elements have different atomic numbers A neutral atom has no net overall charge so Z number of protons number of electrons Learning Check o State the number of protons in each A nitrogen atom N 7 protons A sulfur atom S 16 protons A barium atom Ba 56 protons An atom Page 3 Chemistry 111 Name Of an element is electronically neutral the net charge of an atom Has an equal number of protons and electrons Of aluminum has 13 protons and 13 electrons the net charge is number of protons number of electrons is zero zero 13 Protons 13 13 Electrons 13 0 o Mass Number The Mass Number A Represents the number of particles in the nucleus Is equal to the Number of protons Z number of neutrons 26Fe Mass number is 56 and 26 is the atomic number 56 o Number of neutrons mass number atomic number 56 26 30 Element Symbol Atomic Number Z Mass Number A Number of Protons Number of Neutrons Number of Electrons 1 7 26 79 1 14 57 197 1 7 26 79 0 7 31 118 1 7 26 79 Hydrogen Nitrogen Iron Gold H N Fe Au Isotopes o Isotopes are atoms of the same element that have a different number of neutrons Mass Number A Atomic Number Z 35 17 Cl 37 17 Cl Nuclear Symbol Nuclear Symbol o Number of Protons 17 o Number of Electrons 17 o Number of Neutrons 35 17 18 17 17 37 17 20 Page 4 Chemistry 111 Learning Check Name o Naturally occurring carbon consists of three isotopes C