Question

Write the formula for potassium oxide. why do you not need prefixes in the name ​

Answer 1

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 $\text{O}^{2-}$ 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 $\text{O}^{2-}$ ion is twice that on a $\text{K}^{+}$ ion. Each $\text{K}^{+}$ would pair up with two $\text{O}^{2-}$. Hence the subscript in the formula: $\text{K}_{\bf 2}\text{O}$.

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 $\text{CO}_2$, the prefix di- indicates that there are two oxygen atoms in the formula $\text{CO}_2$. However, there's no need for prefix in ionic compounds such as $\text{K}_2\text{O}$.