Unit 3
TOPIC:
Electron
arrangements
in atoms.
“Not only is the universe stranger than we imagine, it is stranger than we
can imagine.” -Arthur Eddington
Essential Question:
• How are electrons
arranged within the
electron cloud of an
atom?
Electron Arrangement in Atoms
•
Electron Configurations: the way in which
electrons are arranged in orbitals around
the nucleus of the atom
Orbital
• Area in space where an electron is MOST
LIKELY going to be 95% of the time.
• s orbital
•
p orbital
3 rules that tell you how to write the
electron configurations of atoms1. Aufbau Principle – electrons fill in order
from lowest energy level to highest
energy level.
3 rules that tell you how to write the
electron configurations of atoms2. The Pauli exclusion principle
– An orbital can only hold two electrons
that have opposite spins.
3 rules that tell you how to find the
electron configurations of atoms3. Hund’s rule – each
orbital at a given
energy level must
have one electron
in it before any
orbital at that
energy level can
have a second
electron in it.
Fill the orbitals for Nitrogen
Fill the orbitals for Nitrogen
Hund’s Rule
• You must know how many total electrons
can be held by each sublevel. (ie; s can
hold 2, 6 for p, l0 for d, 14 for f)
Orbital Diagrams for IONS
• Ions are atoms that have lost or gained
electrons.
• Examples:
– Sodium
– Sulfur
– Magnesium
– Fluorine
Orbital Diagrams for IONS
• Sodium atom (Na)
• Sodium ion (Na+)
Orbital Diagrams for IONS
• Sulfur atom (S)
• Sulfur ion (S2-)
Orbital Diagrams for IONS
• Magnesium atom (Mg)
• Magnesium ion (Mg2+)
Orbital Diagrams for IONS
• Fluorine atom (F)
• Fluorine ion (F-)
Practice – page 42
• Draw complete orbital diagrams for the
following atoms and ions.
• C, Ne, Al, Al3+, Cl, Cl1• Circle the VALENCE ELECTRONS,
• What do Ne, Al3+, Cl1- have in common?
Writing
Electron
Configurations
(3 ways)
1. Orbital Notation
For each orbital, draw a line______, with the orbital’s name
written underneath the line. An orbital containing one
electron is written as _____, an orbital with two
electrons is written as ____. The lines are labeled
with the principal quantum number (1,2,3 etc. and the
sublevel letter (s, p, d or f).
Example:
Hydrogen ____
Helium __
1s
1s
Lithium ___
1s
____
2s
Carbon ____ ____ ____ ____ _____
1s
2s
2px
2py
2pz
Titanium
2. Electron Configuration Notation
Eliminates the lines and arrows of orbital
notation. Instead, the number of electrons
in a sublevel is shown by adding a
superscript to the sublevel designation.
The superscript indicates the number of
electrons present in that sublevel.
Remember to fill each orbital in the
correct order (1s, 2s, 2p, 3s, 3p, 4s,
etc.)
Write the electron configurations for:
• Calcium (Ca)
• Chlorine (Cl)
• Antimony (Sb)
3. Noble Gas Notation (Short Cut Notation)
• Example: Sodium
[Ne] 3s1
– To simplify sodium’s notation, the symbol for neon,
enclosed in brackets, is used to represent the
complete neon configuration: 1s22s22p6. Sodium
has 11 electrons so the final electron is in the 3s
orbital.
• You can use this notation for any element with
an atomic number greater than 10 – you can
only use noble gases (the far right hand column
of the periodic table) as your “reference”
element (the element in brackets).
– Example: Titanium
Practice – Aluminum (Al)
Electron Configuration:
Practice
Element: Potassium
Electron Configuration:
Shorthand Electron Configuration: