Is HClO4 (Perchloric acid) Ionic or Covalent/Molecular? To tell if HClO4 is ionic or covalent (also called molecular) we look at the Periodic Table that and see that Cl and O are non-metals and H is also a non-metal. When we have all non-metals the compound is usually considered covalent.

Because we have a non-metal and non-metal in HClO4 there will be a difference in electronegativity between O, Cl and H is less than 2.0. This difference results in an electron(s) being shared between the non-metals. The sharing means that the bond will be considered covalent/molecular.

While Perchloric acid is considered covalent, it is considered a strong acid and will dissociate into H+ and ClO4- ions in water.
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Helpful Resources

Metals, Non-Metals on the P- Table: https://youtu.be/OoooStZQHdA
Ionic, Covalent, & Polar Covalent: https://youtu.be/OHFGXfWB_r4
Electronegativity for each element: https://en.wikipedia.org/wiki/Electronegativity
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Because we have a combination of a non-metal and non-metal HClO4 (Perchloric acid) is considered an covalent/molecular compound.

In general, covalent compounds compounds:

- have low melting points and boiling points.
- have low enthalpies of fusion and vaporization.
- do not conduct electricity when dissolved in water.

For more chemistry help, see http://www.Breslyn.org.