Questions? CHEM1010- Fundamentals of Chemistry Notes In order to have a theory, scientists must observe their environment. The old Greeks did so and especially their philosophers had certain ideas of atoms. Leucippus stated that atoms are inseparable building blocks. Date 28/02/20 13 . Helium was discovered on the sun (gk. Helios - God of the Sun) before it was discovered on earth 2 He · Joseph Lockyer did so in 1869 when he harvested light, which splits into different wavelengths Helium 4.0026 · Every element has its very own discrete wavelength spectrum finger print Different frequencies indicate different energy . Its boiling point is the lowest compared to the other elements (-269ºC or 4K!) . It cannot solidify . It comes from decay ... Hence we're running out! It is used as a coolant for magnets . Sir William Ramsay saw the same lines as Lockyer when he observed the fumes of cleveite Electromagnetic spectrum contains all light. Increasing energy 1 Increasing wavelength 0.0001 nm 0.01 nm 10 nm 1000 nm 0.01 cm 1 cm 1 m 100 m Gamma rays X-rays Ultra- violet Infrared Radio waves Radar TV FM AM Visible light 400 nm 500 nm 600 nm 700 nm · Light is a wave . The amplitude of a wave is how high it is measured from the base line Strong - high amplitude Weak - small amplitude . Frequency is how many times the light passes a certain point per second (units: hz)
The frequency of light is the speed of light divided by wavelength The energy of light is the number of photons times their frequency times Planck's constant 6.626×10-34Js c V= In practical experiments light has been proven to be able to push electrons off which gives it particle properties. So the theory goes that light is a package of energy on a wave -- > a photon of light. Light is only a synonym for electromagnetic radiation. Some calculations: c Where c = the velocity of light 3x108m And v = frequency v And ^ = wavelength The particulate properties of light are known as "quanta" AE=nhv where n is an integer indicating the number of photons. A, one, quantum of energy is hv. In subatomic systems energy is given off and accepted in whole packets which means there is no such thing than half a photon. 4.2 What is the energy of a photon of red light with a wavelength of 655nm? 2 3E8 V= 655E-9 v=458015 E 14 AE=nhv AE=1×6.626E-34×458015 E 14 AE=3.035 E-19 What about per mole? - Use Avogadro's constant. 3.03E-19×6.02 E23=182.4kJ ENERGY IS QUANTIZED · Electrons (e ) are able to get excited and enter a higher energy level . They absorb the same energy to enter a higher energy level and the energy they emit when they return to their former state. . The different energy levels are unique to every element and will never change . The electron can fall from whatever energy level to whatever energy