1. The Atom

2. Objectives Previous Unit Let’s take this one step further…
To know the three elementary particles which compose atoms.
To understand the development of the atomic model.
Let’s take this one step further…

3. The Atom Today Over time, the model of the atom evolved.
Two early models we saw were:
Thomson’s Plum Pudding Model
Rutherford’s Nuclear Atom
Show video (3:36)

4. The Atom Today
The model proposed by Niels Bohr was the Planetary Model
The central nucleus (like the sun) surrounded by orbiting electrons (like the planets)
Explained that electrons don’t fall into nucleus because they have fixed energy
The Bohr model was an improvement, but was replaced by the…

5. Quantum Mechanical Model
Modern model of the atom
No longer are electrons treated like they travel like “classical” particles (bowling balls)
Focus is on electrons
Electrons are found not in orbits but in “clouds”
Based on probabilities
Area where there is a 90% chance of finding an electron
Electron clouds
Are 3-dimensional
Come in several shapes
Are tied to specific energies
Energy levels fill in special order
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6. Organizing Electrons
Electrons in an atom are organized into different energy levels
1. Principal energy levels have sublevels
2. Sublevels take the form of atomic orbitals
3. Orbitals “contain” electrons

7. Principal Energy Levels (n)
Principal energy levels (n) are numbered
Maximum number of electrons in a level is 2n2
n = x 12 = 2 electrons
n = x 22 = 8 electrons
n = 3
Each principal level has a number of sublevels equal to the level number
n = sublevel
n = sublevels

8. Sublevels Each sublevel contains a certain number of atomic orbitals
Orbitals are regions where it is likely an electron will be found
Each orbital can hold a maximum of 2 electrons
Letters are used to denote orbitals
Orbitals have characteristic shapes

9. Atomic Orbitals Orbital How many per sublevel? Shape s 1 spherical p 3
peanut d 5
4 are double-peanut
1 is a donut-ringed peanut f 7
flower
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10. Orbitals are regions in Space
The energy level of an electron is the region around the nucleus where the electron is likely to be moving.
S orbital is a sphere

11. P orbitals
                                               
Each P orbital can hold two electrons, but they need to have opposite spins
The P sublevel holds 6 electrons

12. Constant Electron-Density Surfaces of the 3d Orbitals
D level orbitals
Each The D sublevel can hold 10 electrons.
Each orbital holds 2 electrons with opposite spins
                                                 

13. The F Sublevel The F sublevel has 7 orbitals
Each orbital can hold 2 electrons with opposite spin
The F sublevel holds 14 electrons

14. Atomic Orbitals s p d f

15. Electrons can change orbitals
Electrons can change orbital, by absorbing energy. When an electron absorbs a quantum of energy, it moves up to a higher orbital.
When the electron falls from a high orbital to a lower orbital, energy is released, and we see light.
Wintergreen mint is an example
We will also see this in our spectroscopy and flame test labs!

16. Atomic Orbitals Electron configurations Before we proceed…
A series of numbers and letters to show which orbitals contain electrons for a given element
Before we proceed…
Aufbau Principle
Electrons enter orbitals of the lowest energy first
Pauli Exclusion Principle
No two electrons can have the same “state”
State = electron’s orbital and its spin
Electrons in the same orbital will have opposite spin
Hund’s Rule
When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with spin in the same direction

17. Aufbau Diagram

18. Orbital Diagrams A box stands for one orbital
An arrow stands for one electron
Each box (orbital) can only hold 2 arrows (electrons)
or to show direction of spin
*Note: There is some overlap of energy levels, so sublevels do not fill in exact numerical order.

19. Orbital Diagrams

20. Orbital Diagram for A Nitrogen Atom
1s s p s     

21. Orbital Diagram for A Fluorine Atom
1s s p s     

22. Orbital Diagram for A Magnesium AtomMg
1s s p s      

23. Learning Check O1
Write the orbital diagram for the electrons in an oxygen atom.

24. Solution O1
Write the orbital diagram for the electrons in an oxygen atom.
1s s p s     

25. Learning Check O2
Write the orbital diagram for the electrons in an iron atom.

26. Solution O2
Write the orbital diagram for the electrons in an iron atom.
1s 2s p s p 3d              

27. Electron Configuration
Once electrons have been placed in boxes, the electron configuration is written.
Write the energy level and letter for every sublevel that holds electrons
Use a superscript to indicate the number of electrons in each sublevel
Example: for Mg – 1s2 2s2 2p6 3s2 Mg
1s s p s      

28. Exceptional Electron Configurations
Filled energy levels are the most stable
Half filled energy levels are the second most stable
Copper, Chromium and Silver are very important examples of how “exceptions” to filling the Aufbaum diagram leads to understanding the charge of transition metals

29. Examples Write electron configurations for: P, Cr, Sn
Now write the electron configuration without the boxes: Mg, Ni
What element has the following electronic configuration:
1s2 2s2 2p6 3s2 3p1
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2
For fun at home: