Accelerated Chemistry

Chapter 4 Notes – Arrangement of Electrons in Atoms

Chapter 4 problem set:

Page 124Chapter Review: 8, 9, 16, 17, 18, 20, 22, 27, 28, 30, 33, 36, 37

4.1Refinements of the atomic model

Models of the atom so far:

Dalton – atoms are like little “bb’s” - then the gets discovered

Thomson – atom is like a “bb”

Rutherford - Gold foil experiment – “bb”

-1909 - Gold Foil Experiment (Rutherford - New Zealand)

- The Experiment: particles from (in the lead box) were released towards a thin sheet of foil. Most of the particles went through and were seen on the screen. alpha particles bounced back.

- Concluded:1 –

2 –

3 –

4 –

-Analogy: if an atom is the size of the Eagle’s stadium, then the nucleus is the

size of a tennis ball floating in the middle of the stadium.

Bohr model of the atom (1913) – Neils Bohr – Danish Physicist

The Bohr model of the atom comes from the idea that light

is

View vision learning example of hydrogen and helium atoms.

The Bohr Atom (1913)

In 1913, Neils Bohr, a Danish physicist proposed:
  • All the positive charge was in the
  • Electrons orbited the nucleus much like planets orbit the sun (at distances)
  • The the electrons to the nucleus, the energy it has.
  • The the electron is from the nucleus, the energy it has.
/

The Electromagnetic Spectrum - Defined

  • Visible light, x-rays, ultraviolet radiation, infrared radiation, microwaves and radio waves are all part of the electromagnetic spectrum

  • The spectrum consists of electromagnetic radiation –
  • Waves can be described by the wave equation which includes velocity (c = speed of ), (λ) and (ν).
  • Wavelength (definition) =
  • Light through prism leads to high energy (violet) low energy (red)
  • ROYGBIV - colors of the spectrum
  • bright line spectrum (bls) - frequencies of light give off by certain substances when is added to them.
  • heat sodium - yellow light
  • heat lithium - red light
  • elements can appear to give off the same color light, but each will have its own
  • bls - used to determine
  • bls - validates Bohr’s idea that electrons to different energy levels and give off different wavelengths of
Light from the sun (white light) appears as a spectrum of light.
  • Continuous Spectrum of Light (definition) = There are discrete, individual wavelengths of light but rather wavelengths appear, one after the other in a continuous fashion
Spectroscopy (definition) = _ .

Show overhead #6

We will use spectroscopes (

) and tests to study elements because each element emits a different spectrum of light when exited .

Bohr proposed that the energy possessed by an e- in a H-atom and the radius of the orbit are (bls)
  • Quantized (definition): a specific value (of energy)

Bohr’s Energy Absorption Process:
  • Light or energy excites an e- from a lower energy level (e- shell) to a ______energy level
  • These energy levels are “ “ (the e- cannot be in between levels), the e- disappears from one shell and reappears in another
  • This absorption or excitation process is called a or

______

  • Ground State Analogy = a spring and two balls

  • When energy is added, the electron is found in the “ .”
  • The ExcitedState (definition) =

______

  • An illustration of Bohr’s Hydrogen atom (from ground to excited state):

  • The atomic line spectral lines - when an e- in an excited state decays back to the state
The Bohr Model - Summary
  1. When an atom absorbs , its electrons are to a higher energy level. When the electron
______, energy is given off in the form of .
  1. Each distance fallen back is a specific
______, and therefore, a specific .
  1. Since electrons can fall from level 5 to 4, 5 to 3, etc., .
Click for animated H-atom:
Bohr's Atom: Quantum Behavior in Hydrogen - /
Bohr also predicted that since electrons would occupy specific energy levels and each level holds a specific number of electrons
  • The maximum capacity of the first (or innermost) electron shell is .
  • Any element with more than twoe-, the extra e- reside in additional

______.

GroupIA / VIA / VIIA / VIIIA
/ / /
Lithium / Oxygen / Fluorine / Neon

Sodium
Electron Configurations for Selected Elements
  • The number of e- per shell = (where n is then number)
  • Animated Example, Atomic structure animation table -
Draw Bohr Models for the elements with atomic numbers 1-10 below

HHe

Li Be

B C N

O F Ne

Bohr Model illustrations for elements 1-20 on the periodic table examples:
IA / VIIIA
H / IIA / IIIA / IVA / VA / VIA / VIIA / He
Li / Be / B / C / N / O / F / Ne
Na / Mg / Al / Si / P / S / Cl / Ar
K / Ca

So, there is a relationship between the main column # and the number of outershell electrons.

  • Column # = the number of electrons

And, there is a relationship between the row # and the number of energy

.

  • Row # = the number of

The Bohr model truly works well for the H atom only – for elements larger than H the model does not work.

In sum, Bohr made 2 contributions to the development of modern atom theory

  • He explained the atomic line spectra in terms of
  • He introduced the idea of quantized electron in the atom

The Bohr atom lasted for about 13 years and was quickly replaced by the model of the atom.The Bohr model is a good starting point for understanding the quantum mechanical model of the atom

Do Ch4 worksheet #1 – question #1

4.2 Quantum numbers and atomic orbitals & 4.3 Electron Configuration

The Bohr model describes the atom as having definite orbitals occupied by ______.

As with all chemistry, we soon learn that the Bohr model is not correct.

Schrödinger (1926) introduced wave mechanics to describe electrons

  • Based his idea that electrons behaved like
  • Electrons show diffraction ( ) properties like .
  • Treats electrons as waves that are found in .
  • Charge Cloud Model

In the 1930’s - 1940’s more work leads to the charge cloud model which

is also known as the quantum mechanical model. This model does not

show the path of - just the most location.

  • Orbitals (definition) =

.

Orbitals are like "rooms" within which electrons "reside".

The s subshell has ___ s-orbital. The p subshell has ____ p-orbitals.

Each orbital can hold at most electrons

See a good online illustration at

So, the Bohr model really isthe

There are many types of orbitals – we can see them on the periodic table

Sublevel / # of orbitals / e- per orbital / Max # of e- per sublevel / Shape of orbital
s
p /
d
/ 5
dxy, dyz, dxz,
dx2 – y2, dz2
f / 7
(too complicated)

- energy levels, sublevels, and total number of electrons per shell

Energy Level (shell) / Sublevel(s) and Electrons / Total # of Electrons per Shell
1
2
3
4
5
6
7

Show transparency of orbitals in each energy level

Bohr Model Examples (1 to 20):

H / He
Li / Be / B / C / N / O / F / Ne
N / Mg / Al / Si / P / S / Cl / Ar
K / Ca

EC for higher atomic #’s

At atomic # 19 (z = 19), a break in the pattern ensues. One would expect that the orbital to fill after 3p would be 3 d, but alas, it is not. 4s is the next level we fill as it has lower energy than 3d. Look at potassium and calcium.

Do Construction of Periodic Table Activity

Electron configurations

- Electrons enter orbitals in a pattern. For the most part, they follow these rules:

Aufbau principle - electrons must fill energy levels before entering

higher level.

examples (do Bohr models and electron configurations):

Element / Bohr Model / Electron Configuration
Oxygen
Potassium
Copper
Silver

Draw diagonal diagram here:

1s2

2s2 2p6

3s2 3p6 3d10

4s2 4p6 4d10 4f14

5s2 5p6 5d10 5f14

6s2 6p6 6d10

7s2 7p6

-Kernal Electrons: shell electrons

-Valence Electrons: shell electrons

Pauli Exclusion principle - electrons occupying the same orbital must have

spin.

electron spin- clockwise or counterclockwise

Pauli exclusion principle - 2 electrons in the same orbital must have spins.

Hund’s rule ( better known as the Stinky Bus Rule) - before any second

electron can be placed in a sub level, all the orbitals of that sub level must

contain at least electron.

Orbital notation is another way to represent arrangement in atoms.

Examples: Bohr Model, Electron Configuration, and Orbital Notation:

Element / Bohr Model / Electron Configuration / Orbital Notation
Argon /
1s 2s 2p 3s 3p
Manganese /
1s 2s 2p 3s 3p
4s 3d

- example Iodine (Bohr model, electron configuration, orbits, and orbital notation:

5p

- Exceptions to the Aufbau Principle

- Cr is ______not 4s2 3d4

- Other exceptions:

-students should be able to identify these elements simply based on how many electrons they have.

Do the orbital notation for Copper:

Significance of electron configurations

-Valence shell electrons - electrons involved with bonding

-for n = 5, pattern is very complicated - no atom has more than valence electrons

-Noble gases - valence electrons - reactive of all elements

-kernel - part of the atom of valence electrons (includes the nucleus)

-example - sodium kernel =

-examples (find the outershell electron configuration, shorthand notation, and Lewis dot diagram –

Element / Outershell Electron Configuration / Shorthand Notation / Lewis Dot Diagram
Oxygen
Chlorine
Iron
Cobalt
Potassium
Strontium
Silver
K+1
O-2
Quantum numbers show the “addresses” of electrons – each electron has 4 different quantum numbers:
  1. principle (n):
  1. azimuthal (l):
  1. magnetic –
  1. spin -

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