3. Four Quantum Numbers That
Describes Electrons
principal
quantum
number (n)
angular
momentum
quantum
number (ℓ)
magnetic
quantum
number (mℓ)
spin quantum
number (ms)
4. principal quantum number (n)
The principal quantum number (n), describes the energy of the electron.
The energy of the electron is determined by its average distance from the nucleus
or the principal energy level where it is.
The larger n is, the greater the average distance of an electron in the orbital from
the nucleus and therefore the larger (and less stable) the orbital.
The maximum number of electrons possible in a given shell is 2n2 .
6. azimuthal or
angular
momentum
quantum
number (ℓ)
• The azimuthal or angular momentum
quantum number (ℓ), tells us the
“shape” of the orbital.
• It designates the sublevel which the
electron is said to occupy.
• It is also an integer, but its values are
limited to a range of 0 to n-1.
9. magnetic quantum
number (mℓ)
The magnetic quantum number
(mℓ) describes the orientation of
the orbital in space.
The number is also an integer, and
its values are restricted to a range
of +1 down through 0 to -1.
10. spin quantum number (ms)
The spin quantum number (ms) refers to the “spin” of an electron in a
given orbital.
It can have only two values: arrow up ↑ is +1/2( referred to as “spin up”)
and arrow down ↓ is -1/2 ( referred to as “spin down”).
The spin of an electron can be one of two opposite directions, clockwise
or counterclockwise.
Since the spin quantum number has only two possible values, it follows
that an orbital can accommodate a maximum of two electrons only
12. Electron Configuration
The arrangement of electrons in an atom is called the atom’s
electronic configuration. The electron configuration of an atom or
element describes how electrons are distributed in its atomic
orbitals. Since low-energy systems are more stable than high-energy
systems, electrons in an atom tend to assume the arrangement that
gives the atom the lowest energy possible. The most stable, lowest
energy arrangement of the electrons is called ground-state electron
configuration of an element.
13. Electron configurations are based
primarily on three principles:
Aufbau
principle
Pauli
exclusion
principle
Hund’s Rule
14. The Aufbau
Principle
• Aufbau principle is named after the German
word “Aufbeen” which means “build up”.
• The Aufbau principle dictates that electrons
will occupy the orbitals having lower
energies before occupying higher energy
orbitals based on the principal energy levels
and sublevels where they are in.
15. The Pauli
Exclusion
Principle
• Electrons in orbitals can be represented by
arrows in boxes. An electron is able to spin in
only one of the two directions. An arrow
pointing up represents an electron which is
spinning in one direction, and an arrow
pointing down means that the electron is
spinning in the opposite direction.
• The Pauli exclusion principle states that “a
maximum of two electrons, each having
opposite spins, can fit in a single atomic
orbital.” Wolfgang Pauli (1900-1958), an
Austrian physicist, proposed this principle
after observing atoms in excited states.
16. Hund’s Rule
of
Maximum
Multiplicity
• This rule describes the order in which
electrons are filled in all the orbitals
belonging to a subshell.
• It states that “every orbital in a given
subshell are singly occupied by electrons
before a second electron is filled in an
orbital.”
19. Orbital
Diagram
• Orbital diagram consists of boxes
and arrows that represent the
orbitals and the electrons,
respectively. Each box is labeled
with the principal quantum
number and sublevel associated
with the orbital.
20. Noble Gas
Notation
• A shorthand method of writing electron
configuration of atoms uses the noble gases
core such as [He core] to represent 1s2; [Ne
core] to represent the 1s2 2s2 2p6; and other
noble gases.
21.
22. Important data that can be gathered from the
shortened electronic configuration are the
valence configuration and the valence
electrons: the number of electrons in the
outermost subshells.
23. Valence Configuration & Valence Electrons
• The electronic
configuration representing
the outermost subshells is
called valence
configuration.
• Electrons in the outermost
main energy level or
orbital are called valence
electrons.
25. Valence Electrons & Electron-dot
Structure
Valence electrons are involved
in forming chemical bonds.
Chemists used a shorthand
method to visually represent
valence electrons. This is
called as the electron-dot
structure.
An atom’s electron-dot
consists of the element’s
symbol, which represents the
atomic nucleus and inner-level
electrons, surrounded by dots
representing all of the atom’s
valence electrons
26. Steps in
writing the
electron-dot
structure of an
atom:
1. Write the symbol of the given
atom.
2. Determine its valence electron.
This is equal to the number of
dots at the sides of the atom.
3. Draw a dot or dots to represent
the valence electron/s one at a
time on the four sides of the
symbol. (Dots may be placed in
a sequence.)
4. Then paired up the dots.
27. Ionic Lewis Dot Structures
1. Sodium, 11Na, combines with chlorine, 17Cl, to form sodium chloride
(table salt), NaCl.
28. Ionic Lewis Dot Structures
2. Potassium atom, 19K, combines with bromine atom, 9F, to form
potassium bromide, KF.
