Chapter 5
“Electrons in Atoms”
Location of the Electrons
• Are located in an area around the nucleus known as the
Electron Cloud.
• They Move In specific paths, or orbits, at different levels.
The paths are called orbitals or sublevels.
The levels are called energy levels.
An amount of fixed energy separates one level from
another.
The electron cannot exist between energy levels
• A quantum of energy is the amount of energy required to move
an electron from one energy level to another
Energy Levels
• Energy levels- (aka: Principal quantum number) are fixed amounts of energy
located in a specific region around the nucleus.
• 1st energy level- located closest to the nucleus and has the least amount of energy. Can
hold 2 electrons.
• 2nd energy level- located higher than the 1st level. Holds more energy and up to 8
electrons.
• As you go farther from the nucleus, the energy levels hold more electrons and more
energy.
• Within each energy level, there are sublevels depending on the amount of
energy it can hold. The sublevels (orbitals) are named, s, p, d and f.
• As you go farther from the nucleus, more energy is held in the energy levels
and there are more sublevels (orbitals) in each.
• You can find how many energy levels an atom has by which row it is located in
on the periodic table. Example: Calcium is in row 4, therefore it has 4 energy
levels.
Sublevels (orbitals)
• The sublevels are s, p, d and f.
• There is one s sublevel in each energy level. It holds 2 electrons.
• The p sublevel has 3 orbitals each holding 2 electrons. (total 6
electrons)
• The d sublevel has 5 orbitals, each holding 2 electrons (total 10
electrons)
• The f sublevel has 7 orbitals, each holding 2 electrons (total 14
electrons)
• The sublevels are named due to the shape of the travelling path of
the electrons in those orbitals. See next slide.
S
d
p
S
S
d
p
p
p
p
d
p
d
d
Location of the sublevels on the periodic table
Energy level=each row.
There are 7 rows
What sublevels do each
energy level contain:
• Energy level 1- s
• Energy level 2= s, p
• Energy level 3= s,p,d
• Energy level 4= s,p,d,f
• Energy level 5= s,p,d,f
• Energy level 6= s,p,d,
• Energy level 7= s,p
Energy levels and the sublevels it contains:
• Energy level 1- s
• Energy level 2= s, p
• Energy level 3= s,p,d
• Energy level 4= s,p,d,f
• Energy level 5= s,p,d,f
• Energy level 6= s,p,d,
• Energy level 7= s,p
Below: shows the order that the electrons fill the
orbitals. The d orbitals fill after the higher level s
orbitals.
Electrons can move energy levels
• Ground state- the lowest energy level that an electron belongs to.
• Quantum leap- when an electron absorbs energy it will move to a
higher energy level for a short period of time.
• An electron is known to be in the “exited state”, when it absorbs energy and
takes a quantum leap.
• The electron will eventually release the extra energy as light and
return to its ground state.
• The light release by different electrons have color to them depending on how
much energy the light wave contains.
• Examples: Flame test, Fireworks
Checking for understanding:
What happens when an electron moves to a higher energy level?
What happens when an electron moves to a lower energy level?
Are energy levels with lower amounts of energy closer or farther
from the nucleus of the atom??
Rules for how electrons fill up the energy levels.
•
1)
Three rules tell us how:
Aufbau principle - electrons enter the lowest energy first.
2) Pauli Exclusion Principle – Only 2 electrons max can fill an
orbital- with different spins
3) Hund’s Rule- When electrons occupy orbitals of equal energy,
they don’t pair up until they have to.
• This means that if there are 3 p orbitals one electron will go in each first, and then
they will finish filling up with 2 electrons.
Using Orbital filling diagram to write electron
configuration
• https://youtu.be/jTI-ZkrVvE4
Using the Periodic Table to Write the electron configuration.
Writing Nobel Gas Configurations
1. Write the noble gas symbol
in brackets from the row
before that element.
2. The write the configuration
for the row that the element
is on.
Example: Bromine
e- configuration:
1s22s22p63s23p64s23d104p5
Noble gas config:
Ar 4s23d104p5
Valence Electrons
• Valence electrons= the electrons that are located in
the highest energy level
• Valence configuration: It is the highest energy level s
orbital or s and p orbitals.
• Examples: Bromine : 1s22s22p63s23p64s23d10 4p5
• Valence configuration: 4s24p5
• # of valence electrons = (2 +5) = 7