Filling Orbitals
What is an orbital?
• Orbitals are the “shells” or “levels” that electrons exist at around the
atom
• You can think of them somewhat like the orbits of planets. They
don’t physically exist, but tell you where you can find something.
Filling Orbitals
• New electrons are added in an orderly manner, starting with the
closest orbital and continuing outward.
• Each orbital can only fit so many electrons, so once a closer orbital is
full then the next one will start filling.
Filling Orbitals Continued
• Orbital 1: 2 electrons
• Orbital 2: 8 electrons
• Orbital 3: 8 electrons
• Orbital 4: 18 electrons
Some examples
Ions
• An “ion” is when an atom has more or less electrons than protons
• An atom with too many electrons is
called an “anion” and has a negative charge
C7
• An atom with too few electrons is called
a “cation” and has a positive charge
C+
5
Valence Electrons
• The most important electrons are those on the outer-most shell
• These have a special name: valence electrons
• Valence electrons determine how an element reacts
Valence electrons (2 of them)
Valence electron (1 of them)
Atoms like full orbitals
• If possible atoms like to “team up” with other atoms to make full
orbitals
• This causes them to form bonds where they share electrons
+
Sodium
• Has 1 electron, would
like to lose it so its
“valence” level is full.
=
Chlorine
• Has 7 electrons, would
like to gain one more so
its “valence” level is full.
Sodium chloride (salt)
• Both sodium and
chlorine have a full outer
shell and are happy!
Noble Gases
• Noble gases are elements that naturally have a full outer shell.
• They don’t like to interact with any other elements, hence their name
“nobles.”
Noble gases are often used in lamps because they can be heated without burning