1. ELECTRON CONFIGURATIONS
Atomic Structure
ELECTRON CONFIGURATIONS

3. Development of Atomic Models
Thomson model
In the nineteenth century, Thomson described
the atom as a ball of positive charge containing
a number of electrons.
Rutherford model
In the early twentieth century, Rutherford
showed that most of an atom's mass is
concentrated in a small, positively charged
region called the nucleus.
Bohr model
After Rutherford's discovery, Bohr proposed
that electrons travel in definite orbits around
the nucleus.
Quantum mechanical model
Modern atomic theory described the
electronic structure of the atom as the
probability of finding electrons within
certain regions of space.

4. At high temperatures or voltages, elements in the gaseous state emit light of different colors.
When the light is passed through a prism or diffraction grating a line spectrum results.

5. The Electromagnetic Spectrum
X-rays are part of the electromagnetic spectrum
visible light is part of the electromagnetic spectrum
Infrared light is part of the electromagnetic spectrum
The Electromagnetic Spectrum
10.2

6. Each element has its own unique set of spectral emission lines that distinguish it from other elements.
These colored lines indicate that light is being emitted only at certain wavelengths.
Line spectrum of hydrogen. Each line corresponds to the wavelength of the energy emitted when the electron of a hydrogen atom, which has absorbed energy falls back to a lower principal energy level.
10.3

7. Modern View The atom is mostly empty space Two regions Nucleus
protons and neutrons
Electron cloud
region where you might find an electron

8. Instead of being located in orbits, the electrons are located in orbitals.
An orbital is a region around the nucleus where there is a high probability of finding an electron.

9. Quantum Numbers Four Quantum Numbers: Principal Quantum Number ( n )
Specify the “address” of each electron in an atom
Principal Quantum Number ( n )
Angular Momentum Quantum # ( l )
Magnetic Quantum Number ( ml )
Spin Quantum Number ( ms )

10. Quantum Numbers 1. Principal Quantum Number ( n )
Indicates the number of the energy level
As n increase, size of electron cloud increases.
Energy increases as n increases.
2n2 = maximum # of electrons possible in the energy level
Ex. if n=1, energy level 1, can only have 2 electrons 1s 2s 3s
Courtesy Christy Johannesson

11. Quantum Numbers f d s p 2. Angular Momentum Quantum # ( l )
Describes the sublevel within each energy level
# of sublevels = value of principal quantum number of that level
Ex. n=1, has 1 sublevel
n=2, has 2 sublevels f d s p
Courtesy Christy Johannesson

12. Quantum Numbers s p d f 2. Angular Momentum Quantum # ( l )
The lowest sublevel has been named s.
The second sublevel has been named p
The third sublevel has been named d
The fourth sublevel has been namde f s p d f
Courtesy Christy Johannesson

13. Quantum Numbers s 2. Angular Momentum Quantum # ( l )
There is just one s sublevel , thus it has one orbital that can hold only 2 electrons.
Orbital: space occupied by one pair of electrons. s
Courtesy Christy Johannesson

14. Quantum Numbers 2. Angular Momentum Quantum # ( l )y y y z z z x x x
2. Angular Momentum Quantum # ( l )
There are three p sublevels and thus it has three orbitals that can hold only 2 electrons.

15. Quantum Numbers 2. Angular Momentum Quantum # ( l )
There are five d sublevels and thus it has five orbitals that can hold only 2 electrons.
Courtesy Christy Johannesson

16. Quantum Numbers 2. Angular Momentum Quantum # ( l )
There are seven f sublevels and thus it has seven orbitals that can hold only 14 electrons.
Too complicated to show with drawings.
Courtesy Christy Johannesson

17. Principal Energy Levels 1 and 2
For n=1, it can hold a maximum of 2n2 number of electrons: 2 electrons
For n=2, it can hold a maximum of 2n2 number of electrons: 8 electrons

18. Classwork
P 118 # 6 and p122 # 7,8

19. Quantum Numbers 3. Magnetic Quantum Number ( ml )
Specifies the exact orbital within each sublevel
Courtesy Christy Johannesson

20. Quantum Numbers 4. Spin Quantum Number ( ms )
An orbital can hold 2 electrons that spin in opposite directions.
Indicated by arrows:
The arrows indicate 2 electrons spinning in opposite direction
Courtesy Christy Johannesson

21. General Rules For Writing Electron Configurations
1. Pauli Exclusion Principle
Each orbital can hold TWO electrons with opposite spins.
In the following diagrams boxes represent orbitals.
Electrons are indicated by arrows: ↑ or ↓.
C. Johannesson

22. Electrons fill the lowest energy orbitals first.
2. Aufbau Principle
Electrons fill the lowest energy orbitals first.
The number represents n, the principal quantum number
C. Johannesson

23. 3. Hund’s Rule
Within a sublevel, place one e- per orbital before pairing them.
WRONG
RIGHT
C. Johannesson

24. 1s2 2s2 2p4 O Notation Electron Configuration Orbital Diagram 1s 2s 2p
C. Johannesson

25. WRITING ELECTRON CONFIGURATIONSH ↑
1s1
Superscript indicates number of electrons in orbital 1s
Hydrogen has 1 electron. It will occupy the orbital of lowest energy which is the 1s. He
Helium has two electrons. Both helium
electrons occupy the 1s orbital with
opposite spins. ↑ ↓
1s2 1s

26. Filling the 2s Sublevel Li ↑ ↓ ↑ 1s22s1 Be ↑ ↓ ↑ ↓ 1s22s2 1s 2s 1s 2s
The 1s orbital is filled. Lithium’s third electron will enter the 2s orbital. Be ↑ ↓
The 2s orbital fills upon the addition of
beryllium’s third and fourth electrons. 1s 2s ↑ ↓
1s22s2

27. ↑ ↓ B ↑ ↓ ↑ 1s22s22p1 N ↑ ↓ ↑ ↑ ↑ 1s22s22p3 1s 2s 2p 1s 2s 2p
Filling the 2p Sublevel
1s22s22p1 1s 2s 2p
Boron has the first p electron. The three 2p orbitals have the same energy. It does not matter which orbital fills first. N 1s 2s 2p ↑ ↓
The third p electron of nitrogen enters a different p orbital than its first two p electrons to give nitrogen the lowest possible energy. ↑ ↑ ↑
1s22s22p3

28. V 1s 2s 2p 3s 4s 3p 3d
1s22s22p63s23p64s23d3

29. Classwork p 128 #14

30. Electron Dot Diagrams
The electrons in the outer energy level (called valence electrons) are the most important electrons for chemical reactions.
Lewis electron dot diagrams are used to represent these outer electrons around the symbol of an element.

31. Examples Li Lithium Electron configuration: 1s22s1
Select electrons that are in the outer energy level (the ones with the largest principal quantum number): 1s22s1
Largest principal quantum number is 2 and there is 1 electron in this level Li
Valence electron
1. Symbol of element represents nucleus and all electrons except those in outer level
2. Write the electron configuration of element to determine valence electrons.
3. Each side of symbol represents an orbital, draw dots to represent electrons in that orbital.

32. O Oxygen: 1s22s2 2p4 Oxygen: 1s2 2s2 2p4
Oxygen: has 6 valence electrons (2 +4) O

33. Krypton: 1s22s2 2p6 3s23p6 4s2 3d10 4p6
Krypton: 1s22s2 2p6 3s23p6 4s2 3d10 4p6
krypton: has 8 valence electrons (2 +6) Kr
Classwork p 130 # 15 (Z= atomic number)