Question

Arrange them on the basis of electronegativity of elements increases
H_{​​​​​​2}​​​​​O , NH_{​​​​​3} , HF , CH3
Book Solution
CH3 <NH3 <H2O <HF
My Problem
Electronegativity of C is 2.5 so it is first. Electronegativity of N is 3.0 so it is second.
But how I can differentiate between H2O and HF
Is my way of solving this problem is correct and if not then what is correct way tell me.

Answer 1

Remembering how the electronegativities of nonmetals compare is by using the word FONClBrISCHP. It has a spelling that corresponds with the symbols of many of the nonmetals in decreasing order of electronegativity. F for fluorine, O for oxygen, N for nitrogen. Those are the 3 most electronegative elements. Chlorine is very close behind nitrogen, perhaps they are tied. Then comes bromine, iodine, followed by sulfur, carbon, hydrogen, and phosphorus. So FONClBrISCHP is a very useful word in helping you remember the order of the electronegativities of the nonmetals. So now comparing HF and H2O F is more electro negative than O therefore HF is more electronegative