Characteristics of Atoms
• Atoms are composed of protons, neutrons,
and electrons.
• Protons and neutrons are located in the
nucleus (center of the atom).
• Electrons are located outside of the nucleus.
Timberlake LecturePLUS 2000
Quantum Model
• We learned about:
– Dalton’s atomic theory
– J.J. Thompson’s plum pudding model of the atom
– Rutherford’s model of the atom
– Bohr model of the atom
• The model used today is called the quantum
model
Orbitals are represented by a letter (s, p, d, f, …)
Describing Electrons
• There are two ways to express the number
and location of electrons in an atom:
– Orbital Diagrams
– Electron Configurations
Timberlake LecturePLUS 2000
Orbital Diagrams
• Visual representation of how electrons are
placed in orbitals.
• Electrons are represented by arrows.
• In an orbital diagram, electrons have
opposite spins (designated by opposite arrow
directions).
Timberlake LecturePLUS 2000
Increasing energy
Blank Orbital Diagram
7s
6s
5s
4s
3s
2s
7p
6p
5p
4p
6d
5d
4d
3d
3p
2p
1s
Timberlake LecturePLUS 2000
• Fill in the lowest
energy orbitals first!
5f
4f
Electron Configuration
• Tells us the most likely position of where
electrons can be found.
• It is like the address of an electron.
• Electron configurations are used instead of
orbital diagrams because they are less
cumbersome.
Timberlake LecturePLUS 2000
Steps for filling in an Orbital Diagram
1. Identify the number of electrons.
2. Fill in the orbital diagram using the following rules:
A. Aufbau Principle-Fill in the lowest energy orbitals first.
B. Pauli Exclusion Principle-Each orbital (block) can
contain 2 arrows. The arrows must
be pointed in opposite directions.
C. Hund’s Rule Every orbital in a subshell must have one
electron in it before any one orbital can be
filled with a second electron.
Timberlake LecturePLUS 2000
Orbital Diagrams:
Example #1
• Draw an orbital diagram for H.
• Hydrogen has 1 electron.
1s
2s
2p
The electron configuration is then:
1s1
Timberlake LecturePLUS 2000
3s
Orbital Diagrams:
Example #2
• Draw an orbital diagram for B.
• Boron has 5 electrons.
1s
2s
2p
The electron configuration is then:
1s22s22p1
Timberlake LecturePLUS 2000
3s
Orbital Diagrams:
Example #3
• Draw an orbital diagram for C.
• Carbon has 6 electrons.
1s
2s
2p
The electron configuration is then:
1s22s22p2
Timberlake LecturePLUS 2000
3s
Orbital Diagrams:
Example #4
• Draw an orbital diagram for O.
• Oxygen has 8 electrons.
1s
2s
2p
The electron configuration is then:
1s22s22p4
Timberlake LecturePLUS 2000
3s
Practice
Draw an orbital diagram and write the
electron configuration for the following
elements:
1.
2.
3.
4.
5.
He
Li
N
F
S
Timberlake LecturePLUS 2000
He
• Helium has 2 electrons.
1s
2s
2p
The electron configuration is then:
1s2
Timberlake LecturePLUS 2000
3s
Li
• Lithium has 3 electrons.
1s
2s
2p
The electron configuration is then:
1s22s1
Timberlake LecturePLUS 2000
3s
N
• Nitrogen has 7 electrons.
1s
2s
2p
The electron configuration is then:
1s22s22p3
Timberlake LecturePLUS 2000
3s
F
• Fluorine has 9 electrons.
1s
2s
2p
The electron configuration is then:
1s22s22p5
Timberlake LecturePLUS 2000
3s
S
Sulfur has 16 electrons.
1s
2s
2p
3s
The electron configuration is then:
1s22s22p63s23p4
Timberlake LecturePLUS 2000
3p
More Practice
Write the electron configuration for each:
A. Cl
B. Sr
C. I
Timberlake LecturePLUS 2000
Solution
Write the electron configuration for each:
A. Cl (17 electrons)
1s2 2s2 2p6 3s2 3p5
B. Sr (38 electrons)
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
C. I (53 electrons)
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
Timberlake LecturePLUS 2000
Noble Gas Abbreviated Notation
He
Ne
Ar
Kr
Xe
Example
• Write the noble gas abbreviated electron
configuration for oxygen (O).
1.) The noble gas that occurs before O is He.
2.) Start with [He].
3.) Finish writing the electron configuration from
helium:
[He]2s22p4
Example
• Write the noble gas abbreviated electron
configuration for Silicon (Si).
• The noble gas that occurs before Si is Ne.
• Start with [Ne].
• Finish writing electron configuration from Ne:
[Ne]3s23p2
Example
• Write the noble gas abbreviated electron
configuration for Gallium (Ga).
• The noble gas that occurs before Ga is Ar.
• Start with [Ar].
• Finish writing electron configuration from Ar:
[Ar]4s23d104p1
Write the Noble-Gas abbreviated
electron configuration for the
following:
a.) S:
b.) Cd:
c.) Fe:
d.) Br:
Write the Noble-Gas abbreviated
electron configuration for the
following:
a.) S: [Ne]3s23p4
b.) Cd: [Kr]5s24d10
c.) Fe: [Ar]4s23d6
d.) Br: [Ar]4s23d104p5