The Ultimate Guide to Diatomic Nonmetals
Learn about the "Super Seven" elements that exist as pairs in their natural state.
What Are Diatomic Nonmetals?
In chemistry, most elements are stable as individual atoms. However, a special group of seven nonmetal elements are so reactive that they can't exist alone in nature. To become stable, they form a strong covalent bond with another atom of the same element.
The result is a diatomic molecule—a molecule containing two atoms. These seven elements are often called the "Super Seven" or the "HOFBrINCl" elements.
Meet the "Super Seven"
The seven diatomic nonmetals are: Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂), Fluorine (F₂), Chlorine (Cl₂), Bromine (Br₂), and Iodine (I₂).
An easy way to remember them is with the mnemonic:
Have No Fear Of Ice Cold Beer.
Or, you can remember the name "HOFBrINCl" (pronounced "hoff-brinkle").
Location on the Periodic Table
Notice how these elements (except for Hydrogen) form a number "7" on the right side of the periodic table.
Why Do They Form Diatomic Molecules?
The driving force behind the formation of diatomic molecules is the quest for stability. Nonmetal atoms achieve stability by having a full outer shell of valence electrons, just like the noble gases. By sharing electrons with another atom in a covalent bond, both atoms can complete their outer shells.
Single Bond (e.g., F₂)
:F.
..
.F:
..
:F-F:
.. ..
Halogens (F, Cl, Br, I) and Hydrogen have 7 and 1 valence electrons, respectively. They each need one more electron, so they share one pair to form a single bond.
Double Bond (e.g., O₂)
:O:
:O:
:O==O:
Oxygen has 6 valence electrons and needs two more. It shares two pairs of electrons with another oxygen atom, forming a strong double bond.
Triple Bond (e.g., N₂)
Nitrogen has 5 valence electrons and needs three more. It shares three pairs of electrons, forming an exceptionally strong triple bond, which makes N₂ gas very stable.
The Importance of Diatomic Nonmetals
These seven elements are not just a chemistry curiosity; they are fundamental to our world.
Nitrogen (N₂) & Oxygen (O₂)
Together, N₂ (~78%) and O₂ (~21%) make up 99% of the air we breathe. The extreme stability of the N₂ triple bond makes it relatively unreactive, providing a safe, inert atmosphere, while O₂ is essential for respiration and combustion.
Hydrogen (H₂)
As the most abundant element in the universe, hydrogen is the fuel for stars, including our sun. On Earth, H₂ is a clean-burning fuel source with the potential to power future vehicles and industries, producing only water as a byproduct.
The Halogens (F₂, Cl₂, Br₂, I₂)
This group is highly reactive and widely used as disinfectants. Chlorine (Cl₂) purifies our drinking water and swimming pools, while iodine (I₂) is used in antiseptics. Their reactivity makes them crucial in many industrial chemical processes.
Properties and States at STP
At Standard Temperature and Pressure (STP: 0°C and 1 atm), the diatomic nonmetals exist in different states of matter.
| Element | Formula | State at STP | Color |
|---|---|---|---|
| Hydrogen | H₂ | Gas | Colorless |
| Nitrogen | N₂ | Gas | Colorless |
| Oxygen | O₂ | Gas | Colorless |
| Fluorine | F₂ | Gas | Pale yellow-green |
| Chlorine | Cl₂ | Gas | Yellow-green |
| Bromine | Br₂ | Liquid | Red-brown |
| Iodine | I₂ | Solid | Gray-black (sublimes to purple vapor) |
Key Takeaways
- There are seven nonmetal elements that are always diatomic in their pure, elemental form.
- Remember them with the mnemonic "Have No Fear Of Ice Cold Beer" or the name HOFBrINCl.
- They form diatomic molecules by sharing electrons (covalent bonding) to achieve a stable, full outer electron shell, like a noble gas.
- When writing chemical equations, if any of these seven elements are by themselves (not in a compound), you must write them with a subscript of 2 (e.g., O₂, not O).
Frequently Asked Questions
Why aren't the noble gases (like Neon or Argon) diatomic?
Noble gases already have a full outer shell of electrons. They are incredibly stable on their own and have no need to bond with other atoms to gain or share electrons. They are "monatomic" by nature.
What's the difference between O₂ (diatomic oxygen) and O₃ (ozone)?
Both are forms of pure oxygen, known as allotropes. O₂ is the stable, common form we breathe. O₃ (ozone) is a much more reactive and less stable molecule with three oxygen atoms. The "diatomic" label specifically refers to elements that naturally exist as pairs (X₂).
Are there any diatomic metals?
In the gas phase at very high temperatures, some metals like lithium (Li₂) and sodium (Na₂) can form diatomic molecules. However, under normal conditions (solid state), they form metallic lattices, not discrete diatomic molecules. So, for typical high school and introductory chemistry, the answer is no—the "Super Seven" are all nonmetals.