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Certain elements, called "diatomic elements", tend to come in pairs. These elements are:

* Hydrogen (H₂)
* Nitrogen (N₂)
* Oxygen (O₂)
* Fluorine (F₂)
* Chlorine (Cl₂)
* Iodine (I₂)
* Bromine (Br₂)

One way to remember these elements is to make a name out of the symbols. Common ones are HOFBrINCl (pronounced "hoff-brinkle") or H. BrONClIF (pronounced "bron-cliff").

Another way is by use of acronyms. For example:

* Have No Fear Of Ice Cold Beer.
* I Have No Bright or Clever Friends.

A third way is to think of the phrase "7-Up". The "7" signifies the shape made by six of the elements, and the "up" signifies Hydrogen up in the top left corner.

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