Electron configuration

• By the end of this lesson you should be able
to…
• Find an element on the Periodic table by its
Electron configuration
• Write the electron configuration for an
element
• Write noble gas configuration
• Find an element by its noble gas configuration

Music Minute!
• https://www.youtube.com/watch?v=Sw28ppP
QgmE

Review Vocabulary
• Electron – the smallest particle in an atom;
carries a negative charge
• Valence Electron – an electron, located in the
outermost shell of the atom, that can be
transferred to or shared with another atom

• Electron configuration (EC) is a way of
describing how electrons are arranged around
the nucleus.

• Electrons in an atom’s shell are arranged into
energy sublevels which are divided into orbital
• Each individual orbital can hold UP TO 2
electrons. The s- sublevel can hold up to 1
orbital and one orbital holds 2
electrons.
The p- sublevel contains 3 orbitals.
Therefore p can hold up to (3 x 2) =
6 electrons
The d sublevel contains 5 orbitals. It
can hold up to(5 x 2) = 10 electrons
The f sublevel contains 7 orbitals
It can hold up to (7 x 2) = 14
electrons

•This is the Electron Configuration of Hydrogen and a break down
Of its parts.
Number of electrons this
sublevel contains.
Sublevel will tell you max number of electrons it can
hold until it is full
The coefficient (principal energy level) just shows how far down the periodic
periods you need to go to find the element.

•We arrange these orbitals in a chart based on energy levels
where N (the coefficient) corresponds to a period on the
periodic table of elements
• Aufbau principle – Electrons must fill lower energy sublevels
before filling higher energy sublevels
Ex. A neutral atom of Fluorine has 9 electrons (we
know this because the atomic number of a neutral atom tells
us how many protons AND electrons it contains..)
You might think the EC of Fluorine is 1s22p5 but because of
the Aufbau principle you MUST fill all lower energy sublevels
first.
The correct EC of Fluorine is 1s22s22p5.
Notice it goes
1s2s2p3s3p4s3d4p5s4d5p
…. Not always
1,2,3,4,5,6,7…. I’ll
explain why on the next
slide.

The coefficients are not ordered entirely from increasing numerical value
Because of the way the periodic table of elements
Is ordered (increasing number of protons).
Printing this sheet is an easy way to chart EC

• The electron configuration for any element
will always follow this pattern.
• Lets try some examples.

Write the electron configuration for
Oxygen (O)
• To help get you started…
– How many electrons does Oxygen have?
– On which main energy level is Oxygen located?
(main energy level corresponds to the periods on
the periodic table of elements) – plot the
configuration pattern up to that main energy level
– Plot the configuration pattern using the subscripts
to tell how many electrons the sublevel can have

Answer
• Oxygen has 8 electrons
• Oxygen is located on main energy level 2. So
we know that oxygen must fill 1s2 . We have
now accounted for 2 of Oxygen’s 8 electrons.
• 1s22s2 = 8 – 4 = 4 electrons
• 1s22s22p4 is the EC of Oxygen
• Remember – the subscript tells you how many electrons are in each
sublevel. We didn’t need to fill all of 2p’s 6
electron capacity.

What is the EC of Bromine (Br)
• How many electrons does Br have?
• On which main energy level is it located?
– plot the electron configuration up to that
point and account for the electrons remaining
• Plot the configuration pattern using the subscripts to
tell how many electrons the sublevel can have

Answer
• Bromine has 35 electrons
• Bromine is located on the 4th main energy
level - 1s22s2 2p6 3s2 3p6 (count superscripts)
= 18 electrons
• 1s22s22p63s23p6 4s23d10 4p5 = 35 electrons

More examples
• What element’s electron configuration is
1s22s22p63s23p4 ?
Hint: Count the superscripts

Answer
• Sulfur!! Good job!
• When finding an element based on its EC,
count the superscripts because they
correspond to the number of electrons in the
element. This number will also tell you how
many protons, the atomic number, therefore,
identifying the element.

Noble Gas Configuration
• As you go through the elements on the
periodic table, the element’s Electron
Configuration becomes very long. There is a
simpler way to map longer EC’s called Noble
Gas Configuration.
• It’s essentially a shorthand of the shorthand :P

• To write out an element’s configuration using
Noble Gas Configuration find the closest
Noble Gas that comes BEFORE the element.
• Write the Noble Gas in brackets [ ] then the
rest of the orbitals
• NOTE: You can only
put noble gases in the
Brackets.

Write the noble gas configuration for
Rubidium (Rb)
• To help you get started….
– What is the noble gas right BEFORE Rubidium?
– How many electrons does the noble gas have?
– How many electrons does Rubidium have?
– What main energy level is Rubidium in?

Answer
• Krypton is the noble gas right before Rubidium
• [Kr] Krypton has 36 electrons
• Rubidium has 37 electrons
• Rubidium is located in the 5th energy sublevel
• Rubidium’s Noble Gas Configuration is
[Kr]5s1

What is the Noble Gas configuration of
Barium (Ba)?
• To help you get started….
– What is the noble gas right BEFORE Barium?
– How many electrons does the noble gas have?
– How many electrons does Barium have?
– What main energy level is Barium in?

Answer
• [Xe] has 54 electrons
• Barium as 56 electrons
• [Xe]6s2

A good summarization of noble gas
configuration
• https://www.youtube.com/watch?v=nMWmv
w22IR0

Electron configuration

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