Arrangement of Electrons in Atoms Chapter 4

The Development of a New Atomic Model Intro: Rutherford model of the atom was an improvement over previous models, but it was incomplete (Democritus, John Dalton, & J.J Thompson) In the early 20th century, a new atomic model evolved as a result of investigations into the absorption and emission of light by matter. The studies revealed a relationship between light and an atom’s electrons.

Properties of Light The wave Description of Light Electromagnetic radiation: is a form of energy that exhibits wavelike behavior as it travels through space. Ex: X rays, ultraviolet , infrared light, microwaves, and radio waves. Electromagnetic spectrum All forms of electromagnetic radiation move at a constant speed of 3.00 x10^8 m/s

Electromagnetic radiation Electromagnetic radiation: is a form of energy that exhibits wavelike behavior as it travels through space. Wavelength (λ); is the distance between corresponding points on adjacent waves. Expressed in cm or nm Frequency(ν): the number of waves that pass through a specific point in a specific time. Expressed in wave/second hertz ( Hz )- a frequency of one wave per second

Speed of Electromagnetic Radiation Frequency and wavelength are mathematically related to each other. For electromagnetic radiation, the relationship is written as follow: c = λν IF “c” is a constant, then wavelength varies inversely with the frequency of electromagnetic radiation.

1.Determine the frequency of light whose wavelength is 4.257x10^-7 cm. Practice Problem 1.Determine the frequency of light whose wavelength is 4.257x10^-7 cm. 2. What is the wavelength of the electromagnetic radiation whose frequency is 7.500 x10^12 Hz.

The Photoelectric Effect The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal. https://www.youtube.com/wa tch?v=0b0axfyJ4oo&t=2s https://phet.colorado.edu/en/ simulation/legacy/photoelectr ic

The Particle Description of Light A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom. Planck proposed the following relationship between a quantum of energy and the frequency of radiation. E=hv E=energy in joules v= frequency in wave/s or S^-1 h= 6.626 x 10^-34 J.S (Planck’s constant) In 1905, Albert Einstein expanded on Planck’s theory by introducing the radical idea that electromagnetic radiation has a dual wave- particle nature. A photon is quantum of light energy.

Spectra line-emission spectrum- The specific colors (frequencies) of light emitted when an atom returns to the ground state from the excited state. It can be seen when the light is separated by a prism and will give an element a specific spectrum. continuous spectrum- the emission of a continuous range of frequencies of electromagnetic radiation Ground state: lowest energy form of an atom Excited state: higher potential energy than in its ground state.

Bohr Model of the Hydrogen Atom Niels Bohr proposed a hydrogen-atom model that linked the atom’s electron to photon emission. According to the model, the electron can circle the nucleus only in allowed paths, or orbits. The energy of the electron is higher when the electron is in orbits that are successively farther from the nucleus.

Bohr Model of the Hydrogen Atom When an electron falls to a lower energy level, a photon is emitted, and the process is called emission. Energy must be added to an atom in order to move an electron from a lower energy level to a higher energy level. This process is called absorption.

Photon Emission and Absorption