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Electrons in Atoms

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Title: Electrons in Atoms


1
Electrons in Atoms
  • Chapter 5

2
What were early steps in development of atomic
theory?
  • John Dalton Billiard Ball Theory
  • Atom was indivisible
  • J.J. Thomson Plum Pudding Model
  • Atom was composed of smaller particles
  • Rutherford Nuclear Model

3
Rutherford Model
  • Nucleus contains
  • all the positive charge most of mass of atom
  • Nucleus very small
  • only 1/10,000th of atomic diameter
  • Electrons occupy most of volume

4
Later Models
  • Bohr Planetary Model
  • Schrodinger Wave Mechanical Model

5
Problems with the Rutherford Model
  • Why dont electrons crash into nucleus?
  • How are electrons arranged?
  • Why do different elements exhibit different
    chemical behavior?
  • How is atomic emission spectra produced?

6
Atomic Emission Spectra
  • gas in glass tube and apply voltage across ends
  • produces light
  • color of light depends on gas in tube
  • Every element produces its own unique color

7
emission spectrum of element is set of
frequencies (or wavelengths) emitted
8
Why is emission spectra useful?
  • use it to determine if given element is present
    in sample
  • Neon lights

9
Emission Absorption Spectra of Elements
10
Bohr Model
  • Bohr - electrons in atom can have only specific
    amounts of energy NEW idea!
  • Each specific energy is associated with specific
    orbit
  • electrons are restricted to these orbits
  • Bohr assigned quantum number (n) to each orbit
  • the smallest orbit (n 1)
  • is closest to nucleus
  • has lowest energy
  • larger the orbit, more energy it has

11
Bohr Diagram
  • Shows all the electrons in orbits or shells about
    the nucleus.

n2
n3
12
Bohr Model
  • Energy absorbed when electron
  • moves to higher orbit (farther from nucleus)
  • Endothermic process
  • Energy released when electron
  • drops to lower orbit (closer to nucleus)
  • Exothermic process

13
energy levels get closer together the farther
away they are from nucleus
Larger orbits can hold more electrons
14
Max Capacity of Bohr Orbits
15
Electron Transitions
  • If electron gains (absorbs) specific amount of
    energy
  • it can be excited to higher energy level
  • If electron loses specific amount of energy
  • it moves down to lower energy level

16
Hydrogen has 1 electron, but it can make many
possible transitions
17
Absorption Emission
  • cannot easily detect absorption of energy by
    electron
  • BUT
  • can easily detect emission of energy by electron
  • see photon that is kicked out

18
Emitted Light
  • energy of emitted light (E h??
  • matches difference in energy between 2 levels
  • dont know absolute energy of energy levels, but
  • can observe how far apart are from each other

19
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20
ladder often used as analogy for energy levels of
atom How is little bit different?
Potential Energy
21
Ground State vs. Excited State
  • Ground state
  • Lowest energy state of atom
  • electrons in lowest possible energy levels
  • Configurations in Reference Tables are ground
    state
  • Excited state
  • Many possible excited states for each atom
  • One or more electrons excited to higher energy
    level

22
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23
Success of Bohrs Model
  • Bohrs model could predict frequencies in
    emission spectrum of hydrogen
  • Predicted correct size of H atom
  • Unfortunately, didnt work for anything with more
    than 1 electron

24
Which principal energy level of an atom contains
electron with the lowest energy?
  • n1
  • n2
  • n3
  • n4

25
What is total of occupied principal energy
levels in atom of neon in ground state?
  1. 1
  2. 2
  3. 3
  4. 4

26
What is total of fully occupied principal
energy levels in atom of nitrogen in ground state?
  1. 1
  2. 2
  3. 3
  4. 4

27
What is total of electrons in completely
filled fourth principal energy level?
  1. 8
  2. 10
  3. 18
  4. 32

28
Which atom in ground state has five electrons in
its outer level and 10 electrons in its kernel?
  1. C
  2. Cl
  3. Si
  4. P

29
Which electron configuration represents atom in
excited state?
  • a) 2-8-2
  • 2-8-1
  • 2-8
  • 2-7-1

30
Which electron configuration represents atom of
Li in an excited state?
  1. 1-1
  2. 1-2
  3. 2-1
  4. 2-2

31
The characteristic bright-line spectrum of atom
is produced by its
  1. Electrons absorbing energy
  2. Electrons emitting energy
  3. Protons absorbing energy
  4. Protons emitting energy
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