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Potassium oxide: K₂O.

There's no need for prefixes since K₂O is an ionic compound.

Explanation

Find the two elements on a periodic table:

  • Potassium- K- on the left end of period four.
  • Oxygen- O- near the right end of periodic two.

Elements on the bottom-left corner of the periodic table are metals. Those on the top-right corner are nonmetals.

  • Potassium is a metal,
  • Oxygen is a nonmetal.

A metal and a nonmetal combine to form an ionic compound. Potassium oxide is likely to be an ionic compound. It contains two types of ions:

  • Potassium ions: Potassium is group 1 of the periodic table. It is an alkaline metal. Like other alkaline metals such as sodium Na, potassium K tends to lose one electron and form ions of charge +1 in compounds. The ion would be K⁺.
  • Oxide ions from oxygen: Oxygen is the second most electronegative element on the periodic table. It tends to gain two electrons and form the oxide ion [tex]\text{O}^{2-}[/tex] when it combines with metals.

The two types of ions carry opposite charges. They shall pair up at a certain ratio such that they balance the charge on each other. The charge on each [tex]\text{O}^{2-}[/tex] ion is twice that on a [tex]\text{K}^{+}[/tex] ion. Each [tex]\text{K}^{+}[/tex] would pair up with two [tex]\text{O}^{2-}[/tex]. Hence the subscript in the formula: [tex]\text{K}_{\bf 2}\text{O}[/tex].

There are two classes of compounds:

  • Covalent compounds, which need prefixes, and
  • Ionic compounds, which need no prefix.

Prefixes are needed only in covalent compounds. For instance in the covalent compound carbon dioxide [tex]\text{CO}_2[/tex], the prefix di- indicates that there are two oxygen atoms in the formula [tex]\text{CO}_2[/tex]. However, there's no need for prefix in ionic compounds such as [tex]\text{K}_2\text{O}[/tex].

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