CH 101 1st Edition Lecture 5 Outline of Current Lecture I The Original Theories of the Atom II Memorizing the Periodic Table III Using the Periodic Table to find the Charge A Anion B Cation IV Introduction to Elements and Light Current Lecture I Light waves A How to Calculate the Wavelength and the Frequency II The Bohr Model A Absorbing energy B Emitting energy III Recap of Important Equations Current Lecture I Light A form of energy known as electromagnetic radiation and exists as a wave Depending on the frequency of the light wave it will appear as different colors These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Wavelength The distance between crests in a wave One wavelength looks like out of a wave that looks like Wavelength is ALWAYS measured in meters and is represented by the symbol Frequency How many waves pass a given point in one second The frequency is represented as the symbol Frequency is inversely related to the wavelength the longer the wavelength the lower the frequency and the shorter the wavelength the higher the frequency The speed of light is c 3 0x108 m s When calculating the frequency check your answer by checking the exponent because frequencies are usually to the 14 for example 7 3x1014 is a possible frequency whereas 3 15x10 23 it not The unit for frequency is s 1 To find the Frequency or the wavelength of a wave use the equation c Wavelength Frequency c speed of light 3 00x108 m s In many questions the wavelength will be in nm when it should be in meters The conversion between nm and m is m 109 nm Ex Find the frequency of a wave with a wavelength of 700 nm c v c Rearrange the equation so that you re solving for frequency 700 nm 109 m 1 nm 0 0000007 m Convert nanometers to meters v 3 00x108 0 0000007 m 4 3x1014 s 1 Plug in the numbers given and you get 4 3x1014 s 1 Wave Energy The energy of light is directly proportional to the frequency of its wave Wave energy is represented by the equation E h E Energy in Joules h Plank s constant 34 1 6 626x10 J seconds frequency s An easy way to check if you have found the right amount of energy is to look at the exponent Energy is normally to the 19 so if you get an answer that looks like E 1 07x1035 J it is definitely not right Ex If the energy per photon is 3 17x10 19 J find the energy per 1 mole of photons resulting in the units kJ mol The wording may sound tricky but all the question is asking is for you to convert J to kJ and multiply by Avogadro s number 3 17x10 19 J 1 kJ 1000 J There are 1000 Joules in 1 kJ so divide by 1000 3 17x10 19 J 1 kJ 1000 J 6 02x1023 1 mol 191 kJ mol Multiply by Avogadro s number to get kilojoules per mol Different types of waves are determined by the wavelength or the frequency The highest energy wave is a gamma ray Gamma rays have a high frequency and a short wavelength From highest energy to lowest energy the different types of waves are in this order Gamma X ray UV Visible Infrared Micro and Radio Also waves with longer wavelengths are more of a red color and waves with shorter wavelengths have a bluish color Fun fact this is why the sunset in the morning is red orange it s because the light waves with the longest wavelength can travel faster than those with short wavelengths therefore lighting up the sky before the blue light waves can get there Hydrogen Atom Line Spectra When light is shown through a tube of hydrogen certain colors appear because the electrons jump to different energy levels these colors are violet blue indigo and red The frequencies of these colors are red 4 57x10 14 s 1 indigo 6 17x1014 s 1 blue 6 91x1014 s 1 and violet 7 31x1014 s 1 A scientist by the name of Rydberg developed an equation that can gives you the frequency when an atom jumps energy levels by using the hydrogen atom line spectra In his equation h Plank s constant 6 626x10 34 Js R Rydberg s constant 3 29x1015 s 1 n2 low The lowest energy level and n2 high The highest energy level The Rydberg equation Etransition hR n2 low hR n2 high Ex What is the change in energy for the n 3 to n 4 transition E 6 626x10 34 3 29x1015 3 2 6 626x10 34 3 29x1015 4 2 Plug into the equation E 2 42x10 19 1 36x10 19 Solve for the total energy of each energy level then subtract them to find the change in energy E 1 05x10 19 Total change in energy for the n 3 to n 4 transition II The Bohr Model The Bohr model was created when electrons were thought to act as particles the model have many different levels that all very in distance from the nucleus with n 1 being the closest to the nucleus and having the lowest energy The jump between n 1 and n 2 is always going to be greater than the distance between any of the other energy levels The equation Elevel Z2 hR n2 gives you the energy of the electron in the Bohr model In this equation Z the atomic number of the atom h Plank s constant R Rydberg s constant n the energy level This equation is only used when an atom has one electron in the outer shell such as the ion O7 Energy levels on the Bohr model are shown as Ex What is the energy of the electron in the ion He1 if it is in the n 3 energy level E Z2 hR n2 Plug into the equation E 2 2 6 626x10 34 3 29x1015 3 2 Solve and don t forget the negative sign in front of the equation E 9 68x10 19 J Answer make sure it s in Joules A Absorbing energy When an electron jumps to a higher energy level is absorbing and increasing energy If an electron jumps from n 1 to n 2 it is absorbing energy When asked to find the highest or the lowest energy absorption transition remember that the lower the energy levels the farther the jump Ex Determine the highest energy absorption A n 2 to n 5 B n 5 to n 4 C n 1 to n 3 Start by knowing that the jump from n 1 to n 2 is larger than the jump from n 2 to any higher energy level The answer is C n 1 to n 3 because the jump contains the lowest energy levels meaning that it had to jump farther and absorb more energy and it is jumping from a low …