Electrons in Atoms Chapter 4

The New Atomic Model Investigations  relationship between light and atom’s electrons How are electrons arranged? Why don’t they fall into the nucleus?

Light a wave or particle? Wave Description: Electromagnetic Radiation: energy that acts like a wave in space All forms create Electromagnetic Spectrum

Electromagnetic Spectrum

Electromagnetic Spectrum All waves move at speed of light, c, 3.00x108 m/s Waves identified by: wavelength, , the distance b/ corresponding points on adjacent waves. Units: nm, cm, or m Frequency, , # of waves that pass a given point in a specific time, 1 sec. Unit: 1/s = Hertz, Hz

Wavelength and Frequency

Wavelength and Frequency Inverse proportion equation!! Frequency, 1/s speed of light, m/s wavelength, m

Calculation Calculate the wavelength of a radio wave with a frequency of 102.7 x 106s-1 Determine the frequency of light whose wavelength is 5.267 nm.    

Particle Nature of Light Photoelectric Effect: emission of electrons from a metal when light shines on the metal

Photoelectric Effect Light had to be certain frequency to knock e- loose Light must also be a particle! Max Planck(1900) explanation: objects emit energy in small packets called quanta. A photon is a single quantum of (visible) light as well as a single quantum of all other forms of electromagnetic radiation, and can be referred to as a "light quantum".

Max Planck Quantum of energy is the smallest amount of energy that can be lost or gained by an atom E = h Frequency, s-1 Energy of quantum, in joules, J Planck’s constant, 6.626x10-34 Js

Energy Calculation What is the energy of green light, with a wavelength of 500. nm? 500. nm = 5.00 x 10-7 m 1 nm = 10-9 m      

Electromagnetic Spectrum What is the color of an electromagnetic radiation with an energy of 3.4 x10-19 J?

Photoelectric Effect Albert Einstein Light is both wave and particle! Particle of light = photon, having zero mass and a quantum of energy Photons hit metal and knock e- out, but photon has to have enough energy

H-atom Emission Spectrum Pass a current through gas at low pressure it excites the atoms Ground state: lowest energy state of an atom Excited state: atom has higher potential energy than it has in ground state

H – Atom Spectrum When atom jumps from excited state to ground state it gives off energy  LIGHT! E2 Ephoton = E2 – E1 = hv E1

Bohr’s Model of the H Atom (and only H!) Applied quantization of energy transfer to the atomic model Studied atomic spectrum of H to come up with atomic model. Atomic emission spectra: Most sources produce light that contains many wavelengths at once. However, light emitted from pure substances may contain only a few specific wavelengths of light called a line spectrum (as opposed to a continuous spectrum). Atomic emission spectra are inverses of atomic absorption spectra.

Atomic Emission Spectra of C and H Hydrogen: contains 1 red, 1 green, 1 blue and 1 violet. Carbon: Contains many more emission lines as compared to H. Why?

H-atom Line Emission Spectrum

Element Emission Spectras Helium – 23 lines Neon – 75 lines Argon - 159 lines Xenon – 139 lines Mercury – 40 lines

H-atom Line Emission Spectrum More lines in UV (Lyman series) and IR(Paschen series) Why did H-atom only emit certain colors of light?

Bohr Model of H-atom 1913 – Niels Bohr e- circles nucleus in certain paths, orbits or atomic energy levels e- is higher in energy the farther away from nucleus e- cannot be between orbits Video - 23

Bohr Model of H-atom

Bohr Model of H-atom From wavelengths of emission spectrum Bohr calculated energy levels of H-atom Model worked ONLY for H-atom End Part 1