Unit 7: Electrons

1
Unit 7 Electrons
2
Electromagnetic (EM) radiation

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

3
Electromagnetic Spectrum

• Page 120

Frequency and energy have a direct relationship.
4
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

5
Visible Light

• Has wave-like and particle-like properties
• 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

6
Wave properties

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

7
More wave properties

• 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.

8
Energy Amplitude

• DIRECTLY related As energy increases, amplitude
  increases. As energy decreases, amplitude
  decreases
• Determines the intensity of light

Less intense, lower amplitude More
intense, higher amplitude
9
Speed of the wave

• Speed frequency x wavelength
• c ??
• c speed of light 3.00 x 108 m/s (in a
  vacuum)
• as frequency increases wavelength decreases
• This is an inverse, or indirect, relationship.

10
Practice Problem

• What is the wavelength of a radio wave with a
  frequency of 1.01 x 108 Hz?

11
Electrons and Light

• Ground State- the electron occupies the LOWEST
  energy level.
• Excited State- the electron temporarily occupies
  a HIGHER energy level.

12

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

13
Quantum

• The specific amount of energy absorbed needed to
  excite an electron

• The specific amount of energy released when an
  electron falls to the ground state.

Energy in Energy out
14
Atoms and Photons and Color

• Each atoms electrons jump to certain excited
  states.
• 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 atoms electrons can be
  used to identify the element.
• The brightness of the color depends on the number
  of photons emitted.

15
Where are the Electrons in the Cloud?

• Electrons are located at specific distances from
  the nucleus
• Electrons are found to
• have different amounts
• of energy

16
Principal Energy Levels

• 7 Energy Levels
• Abbreviated n
• n 1 is closest to nucleus and has least energy
• n7 is furthest from nucleus and has most energy

17
Energy Levels

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

18
Energy levels contain sublevels

• There are four types of sublevels
• s,
• p,
• d,
• f

19
Sublevels has different energies
s is lowest energy p is
next highest
d follows p in energy f
is highest
20
Energy Sublevels
21
Each sublevel has orbitals that contain electrons
One orbital can contain 2 electrons. They must
have opposite spin. Pauli Exclusion Principle
22
Orbital a place in the electron cloud where an
electron is located.
23
Locating Electrons

• There are two ways to show where the electrons
  are found in the atom
• Orbital filling diagrams
• Electron configurations

24
Follow the rules when placing electrons

• Aufbau Principle- electrons go to the lowest
  energy level first.

25
Follow the rules when placing electrons

• Hunds Rule- no orbital shares electrons until it
  has to share. Space them out to minimize
  repulsion of electrons.

26
Locating Electrons
27
Orbital Filling Diagrams

• Use arrows to represent electrons in orbitals.
• The number of arrows must match the number of
  electrons contained in the atom

28
Practice

• Hydrogen
• Oxygen
• Argon
• Copper

1s1
1s1 2s2 2p4
1s2 2s2 2p6 3s2 3p6
29
Electron Configuration

• Shorthand method for describing the arrangement
  of electrons
• 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

30
Electron Configuration

• Electron Configuration is ordered the way you
  read a book from left to right and top to bottom
• Note that d orbital is 1 energy level behind and
  the f orbital is 2 energy levels behind the s p
  orbitals

The order 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6 etc.
31
Electron Configuration
IA VIIIA
1 s IIA IIIA IVA VA VIA VIIA s
2 s s p p p p p p
3 s s p p p p p p
4 s s d d d d d d d d d d p p p p p p
5 s s d d d d d d d d d d p p p p p p
6 s s f d d d d d d d d d p p p p p p
7 s s f d d

f f f f f f f f f f f f f d
f f f f f f f f f f f f f d
32
Orbital Filling Diagrams
33
Electron Configuration

• Electron Configuration 1s22s22p6
• Orbital Filling Diagram
• Orbital image

34
Noble Gas Configuration

• Shorthand electron configuration
• Give the symbol of the noble gas in the previous
  energy level in brackets
• Give the configuration for the remaining energy
  level
• Example
• Sulfur 1s22s22p63s23p4
• Ne3s23p4

35
Valence Electrons

• Valence electrons found in the outermost energy
  level
• These electrons are used for bonding
• Example Nitrogen 1s2 2s2 2p3
• Add up the number of e- (superscripts) in the
  highest energy level
• Nitrogen has 2 3 5 valence electrons
• Core electrons found in the inner
• energy levels. Nitrogen 1s2 2s2 2p3

36
The number of valence electrons is equal to the
number in the A group
37
Lewis-Dot Diagrams

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

38
Lewis-Dot Diagrams