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Anion Formation

Gain of electrons results in an ion

Atoms Practice
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Octet Rule, Electron Dot Diagrams, Cation Formation, & Anion Formation

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The Octet Rule

The octet rule states that atoms will always want a full outer shell of electrons, which usually is eight electrons. Describe how this rule explains why noble gases are unreactive, and one exception to the octet rule.


Atoms can either gain or lose electrons by following the octet rule. Which type of elements typically lose electrons? Which type typically gain electrons?


Electron Dot Diagrams

Recall that electron dot diagrams show the number of valence electrons in an atom, by drawing dots around the elemental symbol. These diagrams are used to help us to better visualize which atoms will bond together, using the octet rule.

Element Valence Electrons

Dot Diagram



Cation & Anion Formation

Tip: Cations are positive. A trick for this is that the "t" in cation looks like a "+". "Ca+ions" are positive.

Cations are atoms that lose electrons and gain a positive charge. Using the tendencies of element types in the octet rule, name the type of element types that typically forms cations and anions.


Recall that isoelectronic atoms have the same electron configuration. Are Mg2+ and Al3+ isoelectronic? Na+ and Mg2+?

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