1. Chemistry
Ions

2. Electron Configurations of Noble Gases
Write out the electron configuration for the following elements:
Neon
Argon

3. Noble Gases Neon can also be written: (He) 2s2 2p6
Argon can also be written: (Ne) 3s2 3p6
Krypton can be written: (Ar) 3d10 4s2 4p6
What do all of the above have in common?

4. Noble Gases are the Least Reactive Elements
The noble gases show almost no reactivity.
Because each of the noble gases have a full outer energy level, they are stable.
In most chemical reactions, atoms tend to match the s and p electron configurations of noble gases.
A xenon atom. Notice that the outer electron shell has 8 electrons and is therefore full. This makes xenon extremely un-reactive.

5. The Octet Rule
The octet rule is a concept of chemical bonding theory that atoms tend to have either empty valence shells or full valence shells of eight electrons.
When elements combine,
they become more stable
if they both achieve an
“octet” of electrons.

6. Ions
An ion is an atom (or group of atoms) who has either gained or lost one or more electrons.
The number of electrons that are gained or lost depends on the number of valence electrons they have.
What are valence
electrons?

7. Group Numbers Are Related to the Number of Valence Electrons
The number of valence electrons can be easily determined by looking at the group number (of the Main Group Elements):
Which elements would likely lose electrons? Which elements would likely gain electrons?

8. Atoms May Lose Electrons to Form Stable Cations
The Alkali Metals such as Sodium have 1 electron in their outer energy level. Losing this electron will make them have the same electron configuration as a noble gas.
They will then be a positive ion called an cation.

9. Atoms May Gain Electrons to Form Stable Anions
Halogens such as Chlorine have 7 electrons in their outer energy level. Gaining one electron will make them have the same electron configuration as a noble gas.
They will then be a negative ion called an anion.

10. Cations (+) and Anions (-) May Form Ionic Bonds
Sodium chloride (NaCl) is an example of an ionic compound.
Ionic compounds are compounds formed when positive and negative ions are electrically attracted and form a bond. Usually they form when
the cation loses its
electron to form the
anion.