ELECTRONS IN ATOMS Quantum Numbers, Orbitals, And Electron Configurations.
What are electron configurations? The way electrons are arranged in atoms. Used to indicate which...
-
Upload
ethel-rose -
Category
Documents
-
view
222 -
download
0
description
Transcript of What are electron configurations? The way electrons are arranged in atoms. Used to indicate which...
What are electron configurations?
• The way electrons are arranged in atoms.• Used to indicate which orbitals (energy
levels) are occupied by electrons for a particular atom
• The letters s, p, d and f are used to identify sublevels; they represent shapes
Remember!
• Each sublevel orbital holds only 2 electrons but sublevels contain different number of orbitals
s – 1 orbital (maximum 2 e-)p – 3 orbitals (maximum 6 e-)d – 5 orbitals (maximum 10 e-)f – 7orbitals (maximum 14 e-)
Energy Levels
• Different energy levels contain only certain sublevels
Energy level 1 – s sublevel onlyEnergy level 2 – s, p sublevel onlyEnergy level 3 – s, p, d sublevel onlyEnergy level 4 – s, p, d, f sublevel
only
Some rules!
• Aufbau Principle - each electrons is added to the lowest orbital available
• This causes difficulties because of the overlap of orbitals of different energies.
• Pauli Exclusion Principle - at most 2 electrons per orbital - different spins
• Hund’s Rule - When electrons occupy orbitals of equal energy they don’t pair up until they have to .
Electron ConfigurationsFirst Energy Level• only s sublevel (1 s orbital)• only 2 electrons• 1s2
Second Energy Level• s and p sublevels (s and p orbitals are available)• 2 in s, 6 in p• 2s22p6
• 8 total electrons
Third energy level• s, p, and d orbitals• 2 in s, 6 in p, and 10 in d• 3s23p63d10
• 18 total electronsFourth energy level• s,p,d, and f orbitals• 2 in s, 6 in p, 10 in d, and 14 in f• 4s24p64d104f14
• 32 total electrons
So…..
• The electrons fill in the following order:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
Energy Level Diagram
Try it!
• Let’s determine the electron configuration for Phosphorus
• Need to account for 15 electrons
• The first to electrons go into the 1s orbital
• Notice the opposite spins
• only 13 moreIncr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The next electrons go into the 2s orbital
• only 11 more
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The next electrons go into the 2p orbital
• only 5 more
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The next electrons go into the 3s orbital
• only 3 more
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The last three electrons go into the 3p orbitals.
• They each go into separate shapes
• 3 unpaired electrons• 1s22s22p63s23p3
Orbitals fill in order • Lowest energy to higher energy.• Adding electrons can change the energy
of the orbital.• Half filled orbitals have a lower energy,
which makes them more stable.• Changes the filling order
Write these electron configurations
• Magnesium – 12 electrons• 1s22s22p63s2
• Titanium - 22 electrons• 1s22s22p63s23p64s23d2
• Vanadium - 23 electrons • 1s22s22p63s23p64s23d3
Transition Metals are special!
• Draw an energy level diagram and the electronic configuration for:
• Chromium - 24 electrons• 1s22s22p63s23p64s23d4 is expected• But this is wrong!!
Chromium is actually• 1s22s22p63s23p64s13d5
• Why?• This gives us two half filled orbitals.• Slightly lower in energy.• The same principal applies to copper.
Try it!
• Copper has 29 electrons
Copper’s electron configuration
• Copper has 29 electrons so we expect• 1s22s22p63s23p64s23d9
• But the actual configuration is• 1s22s22p63s23p64s13d10
• This gives one filled orbital and one half filled orbital.
• Remember these exceptions