This document discusses the electron configuration of atoms. It begins by introducing the concept of electron configuration and how it describes the distribution of electrons in different energy levels and orbitals within an atom. It then defines the key terms used to describe electron configuration, including principal quantum number, angular momentum quantum number, magnetic quantum number, and orbital diagrams. Finally, it explains the three main rules that govern how electrons fill the orbitals - the Aufbau principle, Pauli exclusion principle, and Hund's rule.

1. Configuration
LESSON 2
The Electron

2. Have you ever played sungka?

3. The goal of the sungka game is to accumulate the
greatest number of shells or stones.
In similar way to determine the number of
electrons in an atom, we can also distribute and
arrange them in a particular order that would
allow us to understand further the characteristics
of an element.

4. • Chemist use this arrangement
known as the electron
configuration to describe and
show the distribution of
electrons in each energy level
located in various locations or
orbitals.
• Bohr’s model of an atom
showed you that electrons are
spread in various energy levels.

5. Big Idea
The electron configuration describes
the location and energy of the
electrons in an atom.

6. • The electron cloud is the region in
the atom where electrons may be
found , or where the electrons are
mostly likely to be found at a
given time.
• As the number of electrons
increases, the electron cloud also
becomes bigger.
Electron Cloud

7. Quantum Numbers
• The atomic orbital describes a region of space in which there is a
high probability of finding electrons .
• Energy changes within an atom as a result of an electron changing
from a wave pattern wit one energy with different energies.
• Each electrons in an atom is described by four different quantum
numbers.
• A quantum numbers is a value that is used when describing the
energy levels of electrons in atoms.

8. Big Idea
The quantum numbers are
used to describe the
location and space in which
an electron may be found.

9. Principal Quantum Number of Main Energy (n)
• The principal quantum number specifies the energy of an
electron and the size of the orbital and its distance away from the
nucleus.
• All orbitals that have the same value of n are said to be in the
same level.
• These are represented by whole numbers. I f n=1, then it means
that the electrons is/are found in the first energy level.

10. Principal Quantum Number of Main Energy
(n)
• If n=2 hen it means that the electrons is/are found in the second
energy level and so on.
• The larger the value of n, the farther it is away from nucleus, and
thus the higher the energy of an electron.

11. Angular Momentum Quantum Number
or Sublevel (1)
• The angular momentum quantum number represents the shape of
the sublevel in each energy level, which may be expressed from 0
to (n-1).
• When a group of orbitals are in the same shape, it is called
subshells or sublevels.

12. Table 11.2 The designated Number for each sublevel

13. • The magnetic quantum number
describes the orientation in space of
an orbital of a given energy (n) and
shape (l). This number divides the
subshell into individual orbitals that
hold the electrons.

14. Figure 11:19 The orientation of the orbitals

15. Orbital Diagrams
• Orbital diagrams are pictorial
representations of the electrons in
an atom .
• We use orbital diagrams to easily
show the distribution of electrons in
each orbital.
1s1 Number of
electrons
Orbital angular
momentum
Principal
quantum
number

16. There are three rules in distribution of the electrons
in each orbital.
Aufbau Principle
Pauli Exclusion
Principle
Hund’s Rule

17. Aufbau Principle
• It states that electrons are filled into atomic orbitals in the increasing
order of orbital energy level.
• According to the Aufbau principle, the available atomic orbitals
with the lowest energy levels are occupied before those with
higher energy levels.

18. Figure 11:20 Arrangement of the orbitals

19. Pauli Exclusion Principle

20. Hund’s Rule
• This rule states that every orbital of the same energy must be singly
occupied one electron before orbital is doubly occupied.
• Fill first all of the empty orbitals before pairing.

21. Look at the two orbital diagram that follow.
Which of the two follows Hund’s rule?

22. Summary of steps on How to write the
electron configuration of an element
1. Determine the atomic number of the element. Remember that in a
neutral atom, the atomic number is also equal to the number of
electrons.
2. Fill the sublevel with the superscript that shows its number of
electrons.
3. Do not forget to take into consideration the maximum number of
electrons in each sublevel.
4. After the sub level 3p, the sequence of the electron configuration varies,
so you need to be familiar with the order of the orbitals as shown in
figure 11.20

23. References
Link for the 3 Rules
• (481) Aufbau Principle | Chemistry – YouTube
• (481) Pauli Exclusion Principle – YouTube
• (481) Hund's Rule | Chemistry - YouTube

24. The End