Unit 7: Electrons 1

Electromagnetic (EM) radiation O A form of energy produced by electrical and magnetic disturbance, or by the movement of electrically charged particles O Can travel in a “vacuum” (they do NOT need a medium) O Travel at the speed of light 2

Electromagnetic Spectrum O Page 120 Frequency and energy have a direct relationship. 3

The Electromagnetic Spectrum Shows all types of EM radiation Shorter wavelength (high-frequency) light has higher energy. –Radio wave light has the lowest energy. –Gamma ray light has the highest energy. High-energy electromagnetic radiation can potentially damage biological molecules. –Ionizing radiation

Visible Light O Has wave-like and particle-like properties O A particle of light is called a photon. Make the colors of the rainbow ROY. G. BIV Each color has a different wavelength, energy, and frequency 5

Wave properties O (f) Frequency-number of waves that pass a given point per unit of time. (Hz) O ( ) Wavelength- distance between similar points in a set of waves (crest to crest.) (m) 6

More wave properties O Amplitude- distance from crest or trough to the normal (baseline). Energy- Waves do not carry energy, they transmit energy. The amount of energy determines the amplitude and the frequency. 7

Energy & Amplitude O DIRECTLY related; As energy increases, amplitude increases. As energy decreases, amplitude decreases O Determines the intensity of light Less intense, lower amplitude More intense, higher amplitude 8

Speed of the wave O Speed = frequency x wavelength c = c = speed of light = 3.00 x 10 8 m/s (in a vacuum) O as frequency increases wavelength decreases O This is an inverse, or indirect, relationship. 9

Practice Problem O What is the wavelength of a radio wave with a frequency of 1.01 x 10 8 Hz? 10

Electrons and Light Ground State- the electron occupies the LOWEST energy level. Excited State- the electron temporarily occupies a HIGHER energy level. 11

Energy is needed to go up a level Photons are released when falling down a level. 12

Quantum O The specific amount of energy absorbed needed to excite an electron O The specific amount of energy released when an electron falls to the ground state. Energy in Energy out 13

Atoms and Photons and Color O Each atom’s electrons “jump” to certain excited states. O Each “fall” releases a photon of a certain wavelength. These wavelengths of light correspond to certain colors of light. The colors of light emitted by an atom’s electrons can be used to identify the element. O The brightness of the color depends on the number of photons emitted. 14

Where are the Electrons in the Cloud? O Electrons are located at specific distances from the nucleus O Electrons are found to have different amounts of energy 15

Principal Energy Levels O 7 Energy Levels O Abbreviated “n” O n= 1 is closest to nucleus and has least energy O n=7 is furthest from nucleus and has most energy 16

Energy Levels O Electrons are restricted to an energy level. O Electrons occupy the lowest energy level possible because electrons are lazy! O On the periodic table, each period (horizontal row) is an energy level

Energy levels contain sublevels O There are four types of sublevels O s, O p, O d, O f

Sublevels has different energies s is lowest energy p is next highest d follows p in energy f is highest 19

Energy Sublevels

Each sublevel has orbitals that contain electrons One orbital can contain 2 electrons. They must have opposite spin. Pauli Exclusion Principle 21

Orbital = a place in the electron cloud where an electron is located.

Locating Electrons O There are two ways to show where the electrons are found in the atom O Orbital filling diagrams O Electron configurations 23

Follow the rules when placing electrons O Aufbau Principle- electrons go to the lowest energy level first. 24

Follow the rules when placing electrons O Hunds Rule- no orbital shares electrons until it has to share. Space them out to minimize repulsion of electrons. 25

Locating Electrons

Orbital Filling Diagrams O Use arrows to represent electrons in orbitals. O The number of arrows must match the number of electrons contained in the atom 27

Practice O Hydrogen: O Oxygen: O Argon: O Copper: 1s 1 1s 1 2s 2 2p 4 1s 2 2s 2 2p 6 3s 2 3p 6 28

Electron Configuration O Shorthand method for describing the arrangement of electrons O Composed of the principal energy level followed by the energy sublevel and includes a superscript with the # of electrons in the orbitals of that sublevel

Electron Configuration O Electron Configuration is ordered the way you read a book: from left to right and top to bottom O Note that d orbital is 1 energy level behind and the f orbital is 2 energy levels behind the s & p orbitals The order: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 14 6d 10 7p 6 etc.

Electron Configuration IAVIII A 1s IIAIII A IV A VAVI A VII A s 2sspppppp 3sspppppp 4ssddddddddddpppppp 5ssddddddddddpppppp 6ssfdddddddddpppppp 7ssfdd fffffffffffffd fffffffffffffd 31

Orbital Filling Diagrams 32

Electron Configuration O Electron Configuration: 1s 2 2s 2 2p 6 O Orbital Filling Diagram: O Orbital image:

Noble Gas Configuration O Shorthand electron configuration 1. Give the symbol of the noble gas in the previous energy level in brackets 2. Give the configuration for the remaining energy level Example: Sulfur = 1s 2 2s 2 2p 6 3s 2 3p 4 [Ne]3s 2 3p 4

Valence Electrons O Valence electrons: found in the outermost energy level O These electrons are used for bonding O Example: Nitrogen = 1s 2 2s 2 2p 3 O Add up the number of e- (superscripts) in the highest energy level O Nitrogen has = 5 valence electrons O Core electrons: found in the inner O energy levels. Nitrogen = 1s 2 2s 2 2p 3

The number of valence electrons is equal to the number in the A group 36

Lewis-Dot Diagrams O Lewis Dot Diagrams are a way to represent the valence electrons in an atom. O Element’s symbol represents the nucleus and inner-level electrons O Dots represent the valence electrons O Dots are placed one at a time on the four sides of the symbol, then paired until all valence electrons are used… O Maximum of 8 e- will be around the symbol 37

Lewis-Dot Diagrams 38