Arrangement of Electrons in the Atom Unit 4

Electrons can often act like light! There is a relationship between light and an atom’s electrons Electrons and light act as a wave and a particle. So to understand electrons we first must understand light!

Light Electromagnetic radiation (light) acts like a wave when it travels through space. But certain characteristics of light cannot be explained just by a wave so we also say it acts as particles…we call this unit a photon

Light is a kind of Electromagnetic radiation.

Wave Anatomy

Wavelength -  Frequency - f Length from one part of a wave to the next identical part Can be measured in any length unit Frequency - f The # of waves that pass by a point in a given amount of time # of waves per second Measured in Hertz Hz (or sec-1)

Frequency and wavelength are related The speed of light is always the same This equation shows us as the wavelength decreases the frequency increases and vice versa

Energy and Frequency are related Higher the frequency, higher the energy Energy is emitted in distinct packets Quantum is the minimum quantity of energy that can be lost or gained by an atom

Practice Problems 1. An X-ray has a wavelength of 1.15 x 10-10 meters. What is its frequency? 2. A purple light has a frequency of 7.42 x 1014 Hz.      A) What is its wavelength?     B) What is the energy of one quanta of light.

Ok back to electrons… The quantum unit for measuring electromagnetic energy is called a photon. Energy must be absorbed for electrons to leave their ground state. Ground state = lowest potential energy Excited state = highest potential energy When an excited electron returns to its ground state, it gives off the energy it gained in the form of EM radiation

Photons Photons are released when electrons fall from a higher orbital to a lower orbital. A photon’s energy is directly related to its frequency.

Bright line spectrum Once the electrons start jumping around they will emit certain wavelengths The wavelength of light will be unique to that element

Spectrum of White Light Is a Continuous Spectrum because white light contains light of all the different wavelength so you see all the colors

Spectrum of Excited Hydrogen Gas Is a Line – Emission Spectrum because only certain bands of colors are visible

Line Spectra of Other Elements So you can determine what element you are looking at based on the wavelengths it emits

Orbitals Electrons reside in orbitals around the nucleus. An electron’s exact location in an orbital CANNOT be determined. Orbital order from lowest to highest energy: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d

1 2 3 4 5 6 7 S - Block P – Block D - Block F- Block

3 Different Types of Notation: Orbital Notation—shows electrons have opposite spins. Long Electron Configuration— Noble Gas Configuration—a shortened form of long notation; it uses the noble gas symbol before the element in question. Ex: Noble Gas Configuration for Zn: [Ar] 4s2 3d10 Zn: [Ar] 4s2 3d10

1 2 3 4 5 6 7 3 4 5 6

Valence Electrons Valence electrons are the electrons located in the outermost s and p orbital. Example) Mg has 2 valence electrons: 1s2 2s2 Sulfur has 6 valence electrons: 1s2 2s2 2p4

To keep track of valence electrons, we use an electron – dot structures Electron dot diagrams represent VALENCE electrons. 1) Write the symbol of the element. 2) Draw dots to represent valence electrons