Arrangement of Electrons in Atoms CHAPTER 4 The

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 20 th 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 x 10^8 m/s

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. 257 x 10^-7 cm. Practice Problem 2. What is the wavelength of the electromagnetic radiation whose frequency is 7. 500 x 10^12 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/watch? v=0 b 0 axfy. J 4 oo&t=2 s https: //phet. colorado. edu/en/simul ation/legacy/photoelectric

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