Question

What is the chemical equation for the formation of $HF$ from the single, isolated $H$ and $F$ atoms?

Answer 1

At room temperature, hydrogen fluoride is a covalently bound chemical. Because of the electronegativity disparity between hydrogen and fluoride, the bond is classified as ionic by some sources.

Complete answer: Hydrogen and fluorine occur in a diatomic gaseous form, ${H_2}$ , under normal conditions, in addition ${F_2}$ correspondingly.
We can see the formation of $HF$ by forming the equation as follows:
${H_2} + {F_2} \to HF$
Now, we will balance the above chemical equation.
We see that there are $2$ Hydrogen and $2$ Fluorine atoms in the reactants side. On the other hand, there is just $1$ Hydrogen and $1$ Fluorine atoms in the product side. Hence, we multiply $2$ on the product side.
${H_2} + {F_2} \to 2HF$
Now, the equation is balanced.
Therefore, the chemical equation for the formation of $HF$ from the single, isolated $H$ and $F$ atoms is ${H_2} + {F_2} \to 2HF$ .

Note:
Since hydrogen is non metallic, the $H - F$ bond (electronegativity difference $1.78$ ) is called polar covalent. The bond between fluorine and a metallic element with the same electronegativity as hydrogen (lead is very close) will be called ionic. $Pb - F$ bond is ionic, while $H - F$ bond is polar covalent.